A core-shell MOF-based gas adsorbent, its preparation method and application

Abstract

This invention relates to the field of gas adsorbent technology, and more particularly to a core-shell MOF-based gas adsorbent, its preparation method, and its application. The MOF-based gas adsorbent of this invention uses UiO-66, engineered for defect control, as the core layer. By introducing glacial acetic acid as a specific regulator, the defect density in the UiO-66 crystal structure is precisely controlled, providing ample physical adsorption space for toluene molecules and forming abundant acidic adsorption sites. The PDA intermediate layer performs the dual functions of "interfacial bonding" and "performance synergy," further enhancing the material's adsorption affinity for toluene and achieving a synergistic improvement in adsorption performance. The superhydrophobic ZIF-8 is used as the outermost shell layer, which serves two purposes: first, it acts as a "molecular barrier" to efficiently block external water molecules from entering the UiO-66 core layer, preventing the core Zr active sites from deactivating due to hydration and solving the stability problem under high humidity conditions; second, it can regulate the diffusion behavior of toluene molecules through molecular sieving effects, achieving highly selective and stable adsorption of toluene under high humidity conditions.

Description

Technical Field

[0001] This invention relates to the field of gas adsorbent technology, and in particular to a core-shell MOF-based gas adsorbent, its preparation method, and its application. Background Technology

[0002] Volatile organic compounds (VOCs) are highly volatile and photochemically reactive. When emitted into the atmosphere, they undergo complex reactions with nitrogen oxides under sunlight to generate ozone, peroxyacetyl nitrate (PAN), and secondary organic aerosols, which in turn cause urban photochemical smog and haze, leading to reduced visibility and damage to ecosystems. At the same time, most VOCs have toxic, irritant, or carcinogenic, mutagenic, and teratogenic effects. Long-term exposure can cause irreversible damage to the human nervous system, liver, kidneys, and hematopoietic function, and increase the risk of cancer. Therefore, all countries have listed them as priority pollutants for control.

[0003] Toluene (C7H8) is one of the most typical and representative VOCs. It is highly volatile, flammable, and toxic, widely used as a solvent and raw material in paint, coatings, resins, and petrochemical production, resulting in high concentrations and large emissions in waste gases. Toluene not only directly irritates the eyes, nose, and throat, causing headaches, dizziness, and ataxia, but long-term exposure can also lead to blood disorders. Furthermore, due to its high reactivity, it rapidly reacts with NOx under sunlight, significantly promoting the formation of ozone and secondary organic aerosols, making it a significant catalyst for urban photochemical smog and haze. Given its dual hazards, countries have set stringent limits on atmospheric toluene emissions. How to efficiently and economically capture and remove toluene from waste gases has become one of the most pressing research topics in the environmental protection field.

[0004] Current advanced purification processes for AMC (aggregate volatile organic compounds) generally employ a "multi-stage filtration + terminal adsorption" architecture. The terminal adsorbent, acting as the final barrier, directly determines whether the outlet concentration can be reduced to the ppb level. Among traditional terminal adsorption materials, activated carbon dominates due to its high specific surface area (over 1000 m² / g). However, its reliance on non-directional physical adsorption has significant limitations: firstly, it has low selective capture efficiency for weakly polar toluene, making precise adsorption of target pollutants difficult; secondly, regeneration is difficult and energy-intensive, and its adsorption performance is significantly affected by ambient humidity, easily dropping sharply under high humidity conditions due to water vapor competition. To optimize activated carbon performance, patent CN119869459A proposes an improved solution. This involves mixing lignin with an activator, then mixing it with fluorocarbons, an initiator, and toluene, and heating to prepare lignin-based super-activated carbon. While this material exhibits some adsorption advantages for low concentrations of toluene under high humidity conditions, fluorocarbons pose potential environmental persistence and bioaccumulation risks, which are detrimental to green manufacturing. Molecular sieves, another type of adsorbent material that has attracted much attention, possess high specific surface area and excellent hydrophobicity, which can alleviate humidity interference to some extent. However, their adsorption of toluene is still mainly physical adsorption, as described in patent CN119303542A. This adsorption mechanism results in weak adsorption retention of toluene by molecular sieves, making them prone to desorption under fluctuating operating conditions and difficult to achieve stable retention of pollutants. In recent years, metal-organic frameworks (MOFs) have shown great application potential in the field of gas adsorption due to their structural advantages of precisely controllable pore size and high specific surface area, providing a new direction for the upgrading of AMC purification technology. For example, patent CN119259005A discloses an iron-based MOF adsorbent for indoor toluene removal. Its core innovation lies in the use of trimesic acid ligands to form π-π bond interactions with toluene molecules, which significantly improves the selective adsorption capacity and adsorption capacity of toluene, achieving the goal of efficient filtration. However, this type of MOF material still has obvious shortcomings - in environments with high air humidity, water molecules easily compete with toluene to occupy adsorption sites, resulting in a significant decrease in the amount of toluene adsorbed, which limits its application in high humidity scenarios. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a core-shell MOF-based gas adsorbent, its preparation method and application. The prepared MOF-based gas adsorbent is a toluene adsorbent with high adsorption capacity, excellent structural stability and excellent water stability, which can achieve efficient and deep removal of low concentrations of toluene.

[0006] The following is a summary of this disclosure to provide a basic understanding of some aspects. This summary is not intended to identify key or important elements, nor is it intended to limit the implementation or any aspects of the claims. Furthermore, this summary provides a simplified overview of some aspects that can be described in more detail in other parts of this disclosure.

[0007] The present invention solves the above-mentioned technical problems through the following technical means:

[0008] In a first aspect, embodiments of the present invention provide a MOF-based gas adsorbent with a core-shell structure, comprising, from the inside out, a MOF core, a polydopamine intermediate layer, and a superhydrophobic modified ZIF-8 shell, wherein the MOF core is defect-engineered UiO-66 or MIL-100(Fe).

[0009] In conjunction with the first aspect, in some embodiments, the raw materials for preparing the MOF-based gas adsorbent include: zinc nitrate hexahydrate, 2-methylimidazole, 2-(pentafluorophenyl)imidazole, and polydopamine-encapsulated MOF core, wherein the polydopamine-encapsulated MOF core is D-UiO-66@PDA or MIL-100(Fe)@PDA, wherein D-UiO-66@PDA is polydopamine-encapsulated defect-engineered UiO-66, and MIL-100(Fe)@PDA is polydopamine-encapsulated MIL-100(Fe).

[0010] In conjunction with the first aspect, in some embodiments, the molar mass ratio of zinc nitrate hexahydrate, 2-methylimidazole, 2-(pentafluorophenyl)imidazole and polydopamine encapsulating the MOF core is (2.0–4.0) mmol : (12.0–18.0) mmol : (0.6–0.9) mmol : (40–80) mg.

[0011] Secondly, embodiments of the present invention also provide a method for preparing a core-shell structured MOF-based gas adsorbent, comprising the following steps:

[0012] Weigh zinc nitrate hexahydrate and 2-(pentafluorophenyl)imidazole and add them to anhydrous methanol to obtain a mixed metal solution; weigh 2-methylimidazole and add it to anhydrous methanol to obtain a 2-methylimidazole solution;

[0013] The dried polydopamine-encapsulated MOF core was dispersed in a metal mixed solution and ultrasonically treated for 20–40 min. Then, a 2-methylimidazole solution was added, and the mixture was stirred at room temperature for 3–5 h. The final product was collected by centrifugation and washed 3–5 times with anhydrous methanol. Finally, it was vacuum dried at 55–70 °C for 10–15 h to obtain the MOF-based gas adsorbent. The polydopamine-encapsulated MOF core was D-UiO-66@PDA or MIL-100(Fe)@PDA powder. D-UiO-66@PDA is polydopamine-encapsulated defect-engineered UiO-66, and MIL-100(Fe)@PDA is polydopamine-encapsulated MIL-100(Fe).

[0014] In conjunction with the second aspect, in some embodiments, the molar mass ratio of zinc nitrate hexahydrate, 2-methylimidazole, 2-(pentafluorophenyl)imidazole and polydopamine encapsulating the MOF core is (2.0–4.0) mmol : (12.0–18.0) mmol : (0.6–0.9) mmol : (40–80) mg.

[0015] In conjunction with the second aspect, in some embodiments, the preparation method of the defect-engineered UiO-66 is as follows:

[0016] Zirconium oxychloride octahydrate and terephthalic acid were weighed and dissolved in N,N-dimethylformamide. The mixture was sonicated and dissolved, then glacial acetic acid was added. The mixture was stirred continuously for 20–40 min and reacted at 120–150 °C for 24–48 h. The solid product was collected by centrifugation and washed 3–5 times with N,N-dimethylformamide and anhydrous ethanol, respectively. Finally, the product was vacuum dried at 80–100 °C to obtain defect-engineered UiO-66. Before use, defect-engineered UiO-66 was activated at 120–150 °C for 2–4 h to remove moisture and small molecule impurities from the pores and restore pore activity.

[0017] In conjunction with the second aspect, in some embodiments, the preparation method of the MIL-100(Fe) is as follows:

[0018] Weigh out ferric nitrate nonahydrate and dissolve it in deionized water to prepare a metal salt solution; weigh out pyromellitic acid and dissolve it in deionized water to prepare a ligand solution.

[0019] Under stirring, the ligand solution was added dropwise to the metal salt solution, and the mixture was reacted at 110–120 °C for 12–18 h. After cooling to room temperature, the product was washed 3–5 times by centrifugation with DMF and anhydrous ethanol, respectively. Finally, the solid product was dried under vacuum at 80–100 °C to obtain MIL-100(Fe). Before use, MIL-100(Fe) was placed at 150–180 °C for 2–3 h to remove moisture and small molecule impurities from the pores and restore pore activity.

[0020] In conjunction with the second aspect, in some embodiments, the preparation method of the polydopamine-encapsulated MOF core is as follows:

[0021] Tris(hydroxymethyl)aminomethane was added to Tris-HCl buffer solution to prepare a buffer mixture. Defect-engineered UiO-66 and MIL-100(Fe) powders were dispersed in the buffer mixture and sonicated for 20-40 min to disperse evenly. Then, dopamine hydrochloride was added and stirred at room temperature for 6-12 h. The precipitate was collected by centrifugation and washed 3-5 times with deionized water until the supernatant was colorless. Finally, the product was vacuum dried at 55-75℃ for 5-8 h.

[0022] In conjunction with the second aspect, in some embodiments, the 2-(pentafluorophenyl)imidazole is prepared as follows:

[0023] Take a reaction vessel and add 2-bromoimidazole, pentafluorophenylboronic acid and tetra(triphenylphosphine)palladium sequentially under an inert atmosphere. Then, inject degassed 1,4-dioxane and sodium carbonate aqueous solution sequentially. Heat to 90-100℃ and stir under reflux for 24-36 hours under nitrogen protection. After cooling to room temperature, pour the reaction solution into ice water and extract with ethyl acetate. Combine the organic phases, wash with saturated brine, dry with anhydrous Na2SO4, filter and concentrate under reduced pressure. The crude product is purified by silica gel column chromatography. Collect the target component, evaporate the solvent to obtain the solid product 2-(pentafluorophenyl)imidazole.

[0024] Thirdly, the embodiments of the present invention also provide the application of the MOF-based gas adsorbent described in the first aspect above, or the MOF-based gas adsorbent prepared by the preparation method described in the second aspect above, in toluene adsorption materials.

[0025] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0026] The MOF-based gas adsorbent of this invention uses UiO-66, regulated by defect engineering, as the core layer. By introducing glacial acetic acid as a specific regulator, the defect density in the UiO-66 crystal structure is precisely controlled. On the one hand, the construction of the defect structure significantly increases the specific surface area and pore volume of the material, providing ample physical adsorption space for toluene molecules. On the other hand, the defect sites expose a large number of open Zr active centers, forming abundant acidic adsorption sites, which become the core active region driving efficient toluene adsorption. In this MOF-based gas adsorbent, the polydopamine (PDA) interlayer performs dual functions of "interfacial bonding" and "performance synergy": the catechin groups and amino functional groups in its molecular structure can efficiently anchor the Zn²⁺ required for subsequent shell growth through coordination, providing stable sites for the uniform nucleation and directional growth of the shell material, ensuring a tight bond between the core and shell structure; simultaneously, the amino groups of PDA itself can form hydrogen bonds with toluene molecules, further enhancing the material's adsorption affinity for toluene and achieving a synergistic improvement in adsorption performance. The MOF-based gas adsorbent of this invention uses superhydrophobic ZIF-8 as the outermost shell layer. It achieves a dual function by utilizing its unique pore structure and hydrophobicity: firstly, it can act as a "molecular barrier" to effectively block external water molecules from entering the core layer UiO-66, preventing the core Zr active sites from being deactivated due to hydration and solving the stability problem under high humidity conditions; secondly, it can regulate the diffusion behavior of toluene molecules through molecular sieving effect, causing them to diffuse slowly and directionally to the highly active adsorption sites in the core layer, ultimately achieving highly selective and stable adsorption of toluene under high humidity conditions.

[0027] The MOF-based gas adsorbent of the present invention is based on a synergistic strategy of "defect engineering-interface coupling-molecular sieving" to construct a "core-intermediate layer-shell" structure MOF that is simple to prepare, structurally stable, and has a leap in performance. This MOF-based gas adsorbent is a toluene adsorbent with high adsorption capacity, excellent structural stability and excellent water stability, and can achieve efficient and deep removal of low concentrations of toluene. Attached Figure Description

[0028] Figure 1 These are the XRD patterns of D-UiO-66, D-UiO-66@PDA, and D-UiO-66@PDA@ZIF-8 in Example 1;

[0029] Figure 2 This is a specific surface area diagram of the MOF-based gas adsorbents prepared in Examples 1-6;

[0030] Figure 3 These are pore size distribution diagrams of the MOF-based gas adsorbents prepared in Examples 1-6;

[0031] Figure 4The water contact angle of the MOF-based gas adsorbents prepared in Examples 1-6;

[0032] Figure 5 The graph shows the dynamic adsorption curves of toluene on the MOF-based gas adsorbents prepared in Examples 1-6.

[0033] Figure 6 This is a graph showing the adsorption capacity of the MOF-based gas adsorbents prepared in Examples 1-6 for toluene.

[0034] Figure 7 The graph shows the toluene adsorption-desorption cycle test results of the MOF-based gas adsorbents prepared in Examples 3 and 5.

[0035] Figure 8 This is a graph showing the adsorption capacity of the MOF-based gas adsorbents prepared in Examples 1-6 for toluene under different humidity conditions. Detailed Implementation

[0036] Reference will now be made to exemplary embodiments, examples of which are shown in the detailed description, implementation, and examples. It should be understood that other implementations may be utilized, and structural and functional changes may be made. Furthermore, features of various implementations may be combined or modified. Therefore, the following description is presented by way of illustration only and should not in any way limit the various alternatives and modifications that may be made to the illustrated implementations. Numerous specific details in this disclosure provide a comprehensive understanding of the subject matter of this disclosure. It should be understood that aspects of this disclosure may be practiced through other implementations, etc., that do not necessarily include all aspects described herein.

[0037] To address the bottlenecks of existing toluene adsorbents, such as low selectivity, easy hydration of active sites, and poor structural stability under high humidity conditions, this application provides a "core-interface coupling-molecular sieving" MOF structure based on a synergistic strategy of defect engineering, interface coupling, and molecular sieving. This strategy results in a simple to prepare, structurally stable, and high-performance MOF with a core-intermediate-shell structure. The core layer is UiO-66, regulated by defect engineering, with the defect density precisely controlled by introducing glacial acetic acid as a specific regulator. A polydopamine (PDA) interlayer serves as both an interface bonding agent and a performance synergist. The outermost shell layer is superhydrophobic ZIF-8. Specifically, the core-shell MOF-based gas adsorbent of this application comprises, from the inside out, a MOF core, a polydopamine interlayer, and a superhydrophobic modified ZIF-8 shell. The MOF core is either defect-engineered UiO-66 or MIL-100(Fe). The raw materials for preparing the MOF-based gas adsorbent include: zinc nitrate hexahydrate, 2-methylimidazole, 2-(pentafluorophenyl)imidazole, and polydopamine-encapsulated MOF core. The polydopamine-encapsulated MOF core is either D-UiO-66@PDA or MIL-100(Fe)@PDA. D-UiO-66@PDA is polydopamine-encapsulated defect-engineered UiO-66, and MIL-100(Fe)@PDA is polydopamine-encapsulated MIL-100(Fe).

[0038] The preparation method of the MOF-based gas adsorbent with a core-shell structure in this application is as follows:

[0039] (1) Synthetic defect-engineered UiO-66, MIL-100(Fe)

[0040] The synthesis method of defect-engineered UiO-66 is as follows:

[0041] Weigh 1.0–3.0 mmol of zirconium oxychloride octahydrate (ZrOCl2·8H2O) and 1.5–3.0 mmol of terephthalic acid (H2BDC), dissolve them in N,N-dimethylformamide (DMF), and sonicate until fully dissolved. Add glacial acetic acid to the above solution and stir continuously for 20–40 min. Transfer the mixed solution to a reaction vessel and react at 120–150 °C for 24–48 h. After the reaction is completed, centrifuge to collect the white solid product, wash it 3–5 times with DMF and anhydrous ethanol, respectively, and finally place the product in a vacuum dryer at 80–100 °C overnight to obtain defect-engineered UiO-66, denoted as D-UiO-66.

[0042] In this step, the molar volume ratio of zirconium oxychloride octahydrate, terephthalic acid, and glacial acetic acid is (1.0–3.0) mmol : (1.5–3.0) mmol : (2–4) mL. D-UiO-66 needs to be activated before subsequent steps. Specifically, D-UiO-66 should be activated at 120–150℃ for 2–4 hours to remove moisture and small molecule impurities from the pores and restore pore activity.

[0043] The synthesis method of MIL-100(Fe) is as follows:

[0044] Weigh 2.5–4.5 mmol of ferric nitrate nonahydrate (Fe(NO3)3·8H2O) and add it to 15 mL of deionized water to obtain a metal salt solution; weigh 3.0–5.0 mmol of trimesic acid (H3BTC) and dissolve it in 15 mL of deionized water to obtain a ligand solution; under vigorous stirring, slowly add the ligand solution dropwise to the metal salt solution, then transfer it to a reaction vessel and react at 110–120 °C for 12–18 h. After cooling to room temperature, wash the product 3–5 times with DMF and anhydrous ethanol, respectively. Finally, dry the solid product under vacuum at 80–100 °C overnight to obtain MIL-100(Fe).

[0045] In this step, the molar ratio of ferric nitrate nonahydrate to trimesolic acid is (2.5–4.5): (3.0–5.0). MIL-100(Fe) needs to be activated before use in subsequent steps. Specifically, MIL-100(Fe) should be activated at 150–180℃ for 2–3 hours to remove moisture, small molecule impurities, etc., from the pores and restore pore activity.

[0046] (2) Preparation of polydopamine-encapsulated MOF cores

[0047] Tris(hydroxymethyl)aminomethane was added to Tris-HCl buffer to prepare a 10 mM, pH 8.5 tris(hydroxymethyl)aminomethane buffer solution. Activated D-UiO-66 and MIL-100(Fe) powders were then dispersed separately in the tris(hydroxymethyl)aminomethane buffer solution and sonicated for 20–40 min to ensure uniform dispersion. Then, 20–50 mg of dopamine hydrochloride was added, and the solution was magnetically stirred at room temperature for 6–12 h. The solution color gradually deepened, turning grayish-black. After the reaction was complete, the precipitate was collected by centrifugation and washed 3–5 times with deionized water until the supernatant was colorless. Finally, the product was vacuum-dried at 55–75 °C for 5–8 h to obtain PDA-encapsulated D-UiO-66 and MIL-100(Fe) powders, named D-UiO-66@PDA and MIL-100(Fe)@PDA.

[0048] In this step, the volume-to-mass ratio of tris(hydroxymethyl)aminomethane buffer, D-UiO-66 and dopamine hydrochloride is (40-100) mL: (50-100) mg: (20-50) mg, and the volume-to-mass ratio of tris(hydroxymethyl)aminomethane buffer, MIL-100(Fe) and dopamine hydrochloride is (40-100) mL: (50-100) mg: (20-50) mg.

[0049] (3) Synthesis of 2-(pentafluorophenyl)imidazolium (Suzuki-Miyaura coupling)

[0050] A magnetic stir bar was placed in a dry reaction flask, and the system was evacuated and purged with nitrogen three times to ensure an inert atmosphere. Then, 2-bromoimidazole (8.0–10.0 mmol), pentafluorophenylboronic acid (8.0–10.0 mmol), and tetra(triphenylphosphine)palladium (0.3–0.5 mmol) were added sequentially. Degassed 1,4-dioxane (40–50 mL) and 2 M sodium carbonate aqueous solution (15–20 mL) were injected sequentially using a syringe. The mixture was heated to 90–100 °C and refluxed under nitrogen protection with vigorous stirring for 24–36 h. In this step, the molar volume ratio of 2-bromoimidazole, pentafluorophenylboronic acid, tetra(triphenylphosphine)palladium, 1,4-dioxane and sodium carbonate aqueous solution is (8.0–10.0) mmol : (8.0–10.0) mmol : (0.3–0.5) mmol : (40–50) mL : (15–20) mL.

[0051] After the reaction was completed, the mixture was cooled to room temperature, poured into ice water, and extracted with ethyl acetate (3×50 mL). The organic phases were combined, washed successively with saturated brine, dried over anhydrous Na2SO4, filtered, and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (petroleum ether / ethyl acetate 1~3:1, v / v). The target component was collected, the solvent was evaporated, and a white solid product 2-(pentafluorophenyl)imidazole was obtained.

[0052] (4) Epitaxial growth of hydrophobic ZIF-8 shell

[0053] 2.0–4.0 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 0.6–0.9 mmol of 2-(pentafluorophenyl)imidazole were dissolved in 80 mL of anhydrous methanol to obtain a metal mixed solution; 12.0–18.0 mmol of 2-methylimidazole (2-MIM) was dissolved in 40 mL of anhydrous methanol to obtain a 2-methylimidazole solution. Dry D-UiO-66@PDA and MIL-100(Fe)@PDA powders were dispersed separately in the metal mixed solution and ultrasonically treated for 20–40 min to allow Zn to precipitate. 2+After the adsorption onto the PDA is complete, the 2-methylimidazole solution is quickly poured into the above mixed solution. The mixture is stirred at room temperature for 3-5 hours, centrifuged to collect the final product, and washed 3-5 times with anhydrous methanol. Finally, it is vacuum dried at 55-70℃ for 10-15 hours to obtain MOF-based gas adsorbents, which are named D-UiO-66@PDA@ZIF-8 and MIL-100(Fe)@PDA@ZIF-8, respectively.

[0054] The following examples 1-10 will provide a detailed description of the core-shell MOF-based gas adsorbent of this application, its preparation method, and its application:

[0055] Example 1

[0056] In this embodiment, the MOF-based gas adsorbent is D-UiO-66@PDA@ZIF-8, and its preparation method is as follows:

[0057] (1) Engineering of defects in synthetic UiO-66

[0058] Weigh 1.5 mmol of ZrOCl2·8H2O and 1.8 mmol of H2BDC and dissolve them in 60 mL of DMF. Sonicate the solution until fully dissolved. Add 3 mL of glacial acetic acid to the solution and stir continuously for 30 min. Transfer the mixture to a reaction vessel and react at 120 °C for 24 h. After the reaction, centrifuge to collect the white solid product. Wash the product three times with DMF and anhydrous ethanol, respectively. Finally, vacuum dry the product overnight at 80 °C to obtain defect-engineered UiO-66, denoted as D-UiO-66. Activate D-UiO-66 at 130 °C for 3 h for later use.

[0059] (2) Preparation of polydopamine-encapsulated MOF cores

[0060] Tris(hydroxymethyl)aminomethane was added to 100 mL of Tris-HCl buffer to prepare a 10 mM buffer solution with pH 8.5. 50 mg of activated D-UiO-66 powder was dispersed in 40 mL of the buffer solution and sonicated for 30 min to ensure uniform dispersion. Then, 30 mg of dopamine hydrochloride was added, and the mixture was magnetically stirred at room temperature for 6 h. The solution gradually changed from a white suspension to a grayish-black color. After the reaction was complete, the precipitate was collected by centrifugation and washed three times with deionized water until the supernatant was colorless. Finally, the product was vacuum-dried at 60 °C for 6 h to obtain PDA-encapsulated D-UiO-66 powder, named D-UiO-66@PDA.

[0061] (3) Synthesis of 2-(pentafluorophenyl)imidazolium (Suzuki-Miyaura coupling)

[0062] A magnetic stir bar was placed in a dry reaction flask, and the system was evacuated and purged with nitrogen three times to ensure an inert atmosphere. Then, 10.0 mmol of 2-bromoimidazole, 10.0 mmol of pentafluorophenylboronic acid, and 0.3 mmol of tetra(triphenylphosphine)palladium were added sequentially. 50 mL of degassed 1,4-dioxane and 15 mL of 2 M sodium carbonate aqueous solution were injected sequentially using a syringe. The mixture was heated to 100 °C and refluxed under nitrogen protection with vigorous stirring for 24 h. After the reaction was complete, the mixture was cooled to room temperature, poured into 100 mL of ice water, and extracted with ethyl acetate (3 × 50 mL). The organic phases were combined, washed sequentially with saturated brine, dried over anhydrous Na₂SO₄, filtered, and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (petroleum ether / ethyl acetate 2:1, v / v). The target fraction was collected, and the solvent was evaporated to obtain a white solid product, 2-(pentafluorophenyl)imidazole.

[0063] (4) Epitaxial growth of hydrophobic ZIF-8 shell

[0064] 2.0 mmol of Zn(NO3)2·6H2O and 0.75 mmol of 2-(pentafluorophenyl)imidazole were dissolved in 80 mL of anhydrous methanol to obtain a metal mixed solution; 15.0 mmol of 2-methylimidazole (2-MIM) was dissolved in 40 mL of anhydrous methanol to obtain a 2-methylimidazole solution. The D-UiO-66@PDA powder prepared in step (2) was dispersed in the metal mixed solution and ultrasonically treated for 30 min to allow Zn to react. 2+ After being fully adsorbed onto the PDA, a 2-methylimidazole solution was quickly poured into the above mixed solution. The mixture was stirred at room temperature for 4 hours, centrifuged to collect the final product, and washed three times with anhydrous methanol. Finally, it was dried under vacuum at 60°C for 12 hours to obtain the MOF-based gas adsorbent, named D-UiO-66@PDA@ZIF-8.

[0065] Example 2

[0066] The difference between the preparation method of D-UiO-66@PDA@ZIF-8 in this embodiment and that in Example 1 is that the mass of dopamine hydrochloride in step (2) is 40 mg, while the rest are the same.

[0067] Example 3

[0068] The difference between the preparation method of D-UiO-66@PDA@ZIF-8 in this embodiment and that in Example 1 is that the mass of dopamine hydrochloride in step (2) is 50 mg, while the rest are the same.

[0069] Example 4

[0070] In this embodiment, the MOF-based gas adsorbent is MIL-100(Fe)@PDA@ZIF-8, and its preparation method is as follows:

[0071] (1) MIL-100(Fe)

[0072] 3.3 mmol of Fe(NO3)3·8H2O was weighed and added to 15 mL of deionized water to obtain a metal salt solution; 3.3 mmol of H3BTC was weighed and dissolved in 15 mL of deionized water to obtain a ligand solution; the ligand solution was slowly added dropwise to the metal salt solution under vigorous stirring, then transferred to a reaction vessel and reacted at 110 °C for 12 h. After cooling to room temperature, the product was washed three times by centrifugation with DMF and anhydrous ethanol, respectively. Finally, the solid product was vacuum dried overnight at 100 °C to obtain MIL-100(Fe). MIL-100(Fe) was activated at 160 °C for 2.5 h for later use.

[0073] (2) Preparation of polydopamine-encapsulated MOF cores

[0074] Tris(hydroxymethyl)aminomethane was added to 100 mL of Tris-HCl buffer to prepare a 10 mM buffer solution with pH 8.5. 100 mg of activated MIL-100(Fe) powder was dispersed in the buffer solution and sonicated for 30 min to ensure uniform dispersion. Then, 20 mg of dopamine hydrochloride was added, and the mixture was magnetically stirred at room temperature for 6 h. The solution gradually darkened to a grayish-black color. After the reaction was complete, the precipitate was collected by centrifugation and washed three times with deionized water until the supernatant was colorless. Finally, the product was vacuum-dried at 75 °C for 6 h to obtain PDA-encapsulated MIL-100(Fe) powder, named MIL-100(Fe)@PDA.

[0075] (3) Synthesis of 2-(pentafluorophenyl)imidazolium (Suzuki-Miyaura coupling)

[0076] A magnetic stir bar was placed in a dry reaction flask, and the system was evacuated and purged with nitrogen three times to ensure an inert atmosphere. Then, 10.0 mmol of 2-bromoimidazole, 10.0 mmol of pentafluorophenylboronic acid, and 0.3 mmol of tetra(triphenylphosphine)palladium were added sequentially. 50 mL of degassed 1,4-dioxane and 15 mL of 2M sodium carbonate aqueous solution were injected sequentially using a syringe. The mixture was heated to 100 °C and refluxed under nitrogen protection with vigorous stirring for 24 h. After the reaction was completed, the mixture was cooled to room temperature, poured into ice water, and extracted with ethyl acetate (3 × 50 mL). The organic phases were combined, washed sequentially with saturated brine, dried over anhydrous Na2SO4, filtered, and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (petroleum ether / ethyl acetate 2:1, v / v). The target component was collected, and the solvent was evaporated to obtain a white solid product, 2-(pentafluorophenyl)imidazole.

[0077] (4) Epitaxial growth of hydrophobic ZIF-8 shell

[0078] 2.0 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 0.8 mmol of 2-(pentafluorophenyl)imidazole were dissolved in 80 mL of anhydrous methanol to obtain a metal mixed solution; 16 mmol of 2-methylimidazole (2-MIM) was dissolved in 40 mL of anhydrous methanol to obtain a 2-methylimidazole solution. The MIL-100(Fe)@PDA powder prepared in step (2) was dispersed in the metal mixed solution and ultrasonically treated for 30 min to allow Zn to precipitate. 2+ After being fully adsorbed onto the PDA, a 2-methylimidazole solution was quickly poured into the above mixed solution. The mixture was stirred at room temperature for 4 hours, centrifuged to collect the final product, and washed three times with anhydrous methanol. Finally, it was dried under vacuum at 60°C for 12 hours to obtain the MOF-based gas adsorbent, named MIL-100(Fe)@PDA@ZIF-8.

[0079] Example 5

[0080] The difference between the preparation method of MIL-100(Fe)@PDA@ZIF-8 in this embodiment and that in Example 4 is that the mass of dopamine hydrochloride in step (2) is 30 mg, while the rest are the same.

[0081] Example 6

[0082] The difference between the preparation method of MIL-100(Fe)@PDA@ZIF-8 in this embodiment and that in Example 4 is that the mass of dopamine hydrochloride in step (2) is 40 mg, while the rest are the same.

[0083] Example 7

[0084] In this embodiment, the MOF-based gas adsorbent is D-UiO-66@PDA@ZIF-8, and its preparation method is as follows:

[0085] (1) Engineering of defects in synthetic UiO-66

[0086] Weigh 1.0 mmol of ZrOCl2·8H2O and 1.5 mmol of H2BDC and dissolve them in 60 mL of DMF. Sonicate the solution until fully dissolved. Add 2 mL of glacial acetic acid to the solution and stir continuously for 20 min. Transfer the mixture to a reaction vessel and react at 130 °C for 30 h. After the reaction, centrifuge to collect the white solid product. Wash the product four times with DMF and anhydrous ethanol, respectively. Finally, vacuum dry the product overnight at 90 °C to obtain defect-engineered UiO-66, denoted as D-UiO-66. Activate D-UiO-66 at 120 °C for 2 h for later use.

[0087] (2) Preparation of polydopamine-encapsulated MOF cores

[0088] Tris(hydroxymethyl)aminomethane was added to 40 mL of Tris-HCl buffer to prepare a 10 mM buffer solution with pH 8.5. 50 mg of activated D-UiO-66 powder was dispersed in the 40 mL buffer solution and sonicated for 20 min to ensure uniform dispersion. Then, 30 mg of dopamine hydrochloride was added, and the mixture was magnetically stirred at room temperature for 8 h. The solution gradually changed from a white suspension to a grayish-black color. After the reaction was complete, the precipitate was collected by centrifugation and washed four times with deionized water until the supernatant was colorless. Finally, the product was vacuum-dried at 55 °C for 8 h to obtain PDA-encapsulated D-UiO-66 powder, named D-UiO-66@PDA.

[0089] (3) Synthesis of 2-(pentafluorophenyl)imidazolium (Suzuki-Miyaura coupling)

[0090] A magnetic stir bar was placed in a dry reaction flask, and the system was evacuated and purged with nitrogen three times to ensure an inert atmosphere. Then, 8.0 mmol of 2-bromoimidazole, 8.0 mmol of pentafluorophenylboronic acid, and 0.4 mmol of tetra(triphenylphosphine)palladium were added sequentially. 40 mL of degassed 1,4-dioxane and 18 mL of 2 M sodium carbonate aqueous solution were injected sequentially using a syringe. The mixture was heated to 90 °C and refluxed under nitrogen protection with vigorous stirring for 30 h. After the reaction was complete, the mixture was cooled to room temperature, poured into 100 mL of ice water, and extracted with ethyl acetate (3 × 50 mL). The organic phases were combined, washed sequentially with saturated brine, dried over anhydrous Na₂SO₄, filtered, and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (petroleum ether / ethyl acetate 1:1, v / v). The target fraction was collected, and the solvent was evaporated to obtain a white solid product, 2-(pentafluorophenyl)imidazole.

[0091] (4) Epitaxial growth of hydrophobic ZIF-8 shell

[0092] 3.0 mmol of Zn(NO3)2·6H2O and 0.6 mmol of 2-(pentafluorophenyl)imidazole were dissolved in 80 mL of anhydrous methanol to obtain a metal mixed solution; 12.0 mmol of 2-methylimidazole (2-MIM) was dissolved in 40 mL of anhydrous methanol to obtain a 2-methylimidazole solution. The D-UiO-66@PDA powder prepared in step (2) was dispersed in the metal mixed solution and ultrasonically treated for 20 min to allow Zn to react. 2+ After being fully adsorbed onto the PDA, a 2-methylimidazole solution was quickly poured into the above mixed solution. The mixture was stirred at room temperature for 3 hours, centrifuged to collect the final product, and washed four times with anhydrous methanol. Finally, it was vacuum dried at 55°C for 10 hours to obtain the MOF-based gas adsorbent, named D-UiO-66@PDA@ZIF-8.

[0093] Example 8

[0094] In this embodiment, the MOF-based gas adsorbent is D-UiO-66@PDA@ZIF-8, and its preparation method is as follows:

[0095] (1) Engineering of defects in synthetic UiO-66

[0096] Weigh 3.0 mmol of ZrOCl2·8H2O and 3.0 mmol of H2BDC and dissolve them in 80 mL of DMF. Sonicate the solution until fully dissolved. Add 4 mL of glacial acetic acid to the solution and stir continuously for 40 min. Transfer the mixture to a reaction vessel and react at 150 °C for 48 h. After the reaction, centrifuge to collect the white solid product. Wash the product five times with DMF and anhydrous ethanol, respectively. Finally, vacuum dry the product at 100 °C overnight to obtain defect-engineered UiO-66, denoted as D-UiO-66. Activate D-UiO-66 at 150 °C for 4 h for later use.

[0097] (2) Preparation of polydopamine-encapsulated MOF cores

[0098] Tris(hydroxymethyl)aminomethane was added to 80 mL of Tris-HCl buffer to prepare a 10 mM buffer solution with pH 8.5. 100 mg of activated D-UiO-66 powder was dispersed in the buffer solution and sonicated for 20 min to ensure uniform dispersion. Then, 20 mg of dopamine hydrochloride was added, and the mixture was magnetically stirred at room temperature for 12 h. The solution gradually changed from a white suspension to a grayish-black color. After the reaction was complete, the precipitate was collected by centrifugation and washed five times with deionized water until the supernatant was colorless. Finally, the product was vacuum-dried at 70 °C for 5 h to obtain PDA-encapsulated D-UiO-66 powder, named D-UiO-66@PDA.

[0099] (3) Synthesis of 2-(pentafluorophenyl)imidazolium (Suzuki-Miyaura coupling)

[0100] A magnetic stir bar was placed in a dry reaction flask, and the system was evacuated and purged with nitrogen three times to ensure an inert atmosphere. Then, 7.0 mmol of 2-bromoimidazole, 7.0 mmol of pentafluorophenylboronic acid, and 0.5 mmol of tetra(triphenylphosphine)palladium were added sequentially. 45 mL of degassed 1,4-dioxane and 20 mL of 2 M sodium carbonate aqueous solution were injected sequentially using a syringe. The mixture was heated to 90 °C and refluxed under nitrogen protection with vigorous stirring for 36 h. After the reaction was complete, the mixture was cooled to room temperature, poured into 100 mL of ice water, and extracted with ethyl acetate (3 × 50 mL). The organic phases were combined, washed sequentially with saturated brine, dried over anhydrous Na₂SO₄, filtered, and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (petroleum ether / ethyl acetate 3:1, v / v). The target fraction was collected, and the solvent was evaporated to obtain a white solid product, 2-(pentafluorophenyl)imidazole.

[0101] (4) Epitaxial growth of hydrophobic ZIF-8 shell

[0102] 4.0 mmol of Zn(NO3)2·6H2O and 0.9 mmol of 2-(pentafluorophenyl)imidazole were dissolved in 80 mL of anhydrous methanol to obtain a metal mixed solution; 18.0 mmol of 2-methylimidazole (2-MIM) was dissolved in 40 mL of anhydrous methanol to obtain a 2-methylimidazole solution. The D-UiO-66@PDA powder prepared in step (2) was dispersed in the metal mixed solution and ultrasonically treated for 40 min to allow Zn to react. 2+ After being fully adsorbed onto the PDA, a 2-methylimidazole solution was quickly poured into the above mixed solution. The mixture was stirred at room temperature for 5 hours, centrifuged to collect the final product, and washed 5 times with anhydrous methanol. Finally, it was vacuum dried at 70°C for 15 hours to obtain the MOF-based gas adsorbent, named D-UiO-66@PDA@ZIF-8.

[0103] Example 9

[0104] In this embodiment, the MOF-based gas adsorbent is MIL-100(Fe)@PDA@ZIF-8, and its preparation method is as follows:

[0105] (1) MIL-100(Fe)

[0106] 2.5 mmol of Fe(NO3)3·8H2O was weighed and added to 15 mL of deionized water to obtain a metal salt solution; 3.0 mmol of H3BTC was weighed and dissolved in 15 mL of deionized water to obtain a ligand solution; the ligand solution was slowly added dropwise to the metal salt solution under vigorous stirring, then transferred to a reaction vessel and reacted at 115 °C for 15 h. After cooling to room temperature, the product was washed four times by centrifugation with DMF and anhydrous ethanol, respectively. Finally, the solid product was vacuum dried overnight at 80 °C to obtain MIL-100(Fe). MIL-100(Fe) was activated at 150 °C for 2 h for later use.

[0107] (2) Preparation of polydopamine-encapsulated MOF cores

[0108] Tris(hydroxymethyl)aminomethane was added to 50 mL of Tris-HCl buffer to prepare a 10 mM buffer solution with pH 8.5. 50 mg of activated MIL-100(Fe) powder was dispersed in the buffer solution and sonicated for 30 min to ensure uniform dispersion. Then, 50 mg of dopamine hydrochloride was added, and the mixture was magnetically stirred at room temperature for 10 h. The solution gradually darkened to a grayish-black color. After the reaction was complete, the precipitate was collected by centrifugation and washed four times with deionized water until the supernatant was colorless. Finally, the product was vacuum-dried at 60 °C for 8 h to obtain PDA-encapsulated MIL-100(Fe) powder, named MIL-100(Fe)@PDA.

[0109] (3) Synthesis of 2-(pentafluorophenyl)imidazolium (Suzuki-Miyaura coupling)

[0110] A magnetic stir bar was placed in a dry reaction flask, and the system was evacuated and purged with nitrogen three times to ensure an inert atmosphere. Then, 10.0 mmol of 2-bromoimidazole, 10.0 mmol of pentafluorophenylboronic acid, and 0.3 mmol of tetra(triphenylphosphine)palladium were added sequentially. 50 mL of degassed 1,4-dioxane and 15 mL of 2M sodium carbonate aqueous solution were injected sequentially using a syringe. The mixture was heated to 100 °C and refluxed under nitrogen protection with vigorous stirring for 24 h. After the reaction was completed, the mixture was cooled to room temperature, poured into ice water, and extracted with ethyl acetate (3 × 50 mL). The organic phases were combined, washed sequentially with saturated brine, dried over anhydrous Na2SO4, filtered, and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (petroleum ether / ethyl acetate 2:1, v / v). The target component was collected, and the solvent was evaporated to obtain a white solid product, 2-(pentafluorophenyl)imidazole.

[0111] (4) Epitaxial growth of hydrophobic ZIF-8 shell

[0112] 2.0 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 0.8 mmol of 2-(pentafluorophenyl)imidazole were dissolved in 80 mL of anhydrous methanol to obtain a metal mixed solution; 16 mmol of 2-methylimidazole (2-MIM) was dissolved in 40 mL of anhydrous methanol to obtain a 2-methylimidazole solution. The MIL-100(Fe)@PDA powder prepared in step (2) was dispersed in the metal mixed solution and ultrasonically treated for 30 min to allow Zn to precipitate. 2+ After being fully adsorbed onto the PDA, a 2-methylimidazole solution was quickly poured into the above mixed solution. The mixture was stirred at room temperature for 4 hours, centrifuged to collect the final product, and washed three times with anhydrous methanol. Finally, it was dried under vacuum at 60°C for 12 hours to obtain the MOF-based gas adsorbent, named MIL-100(Fe)@PDA@ZIF-8.

[0113] Example 10

[0114] In this embodiment, the MOF-based gas adsorbent is MIL-100(Fe)@PDA@ZIF-8, and its preparation method is as follows:

[0115] (1) MIL-100(Fe)

[0116] 4.5 mmol of Fe(NO3)3·8H2O was weighed and added to 20 mL of deionized water to obtain a metal salt solution; 5.0 mmol of H3BTC was weighed and dissolved in 20 mL of deionized water to obtain a ligand solution; the ligand solution was slowly added dropwise to the metal salt solution under vigorous stirring, then transferred to a reaction vessel and reacted at 120 °C for 18 h. After cooling to room temperature, the product was washed five times with DMF and anhydrous ethanol by centrifugation, and finally the solid product was vacuum dried overnight at 80 °C to obtain MIL-100(Fe). MIL-100(Fe) was activated at 180 °C for 3 h for later use.

[0117] (2) Preparation of polydopamine-encapsulated MOF cores

[0118] Tris(hydroxymethyl)aminomethane was added to 40 mL of Tris-HCl buffer to prepare a 10 mM buffer solution with pH 8.5. 50 mg of activated MIL-100(Fe) powder was dispersed in the buffer solution and sonicated for 30 min to ensure uniform dispersion. Then, 20 mg of dopamine hydrochloride was added, and the mixture was magnetically stirred at room temperature for 10 h. The solution gradually darkened to a grayish-black color. After the reaction was complete, the precipitate was collected by centrifugation and washed four times with deionized water until the supernatant was colorless. Finally, the product was vacuum-dried at 75 °C for 6 h to obtain PDA-encapsulated MIL-100(Fe) powder, named MIL-100(Fe)@PDA.

[0119] (3) Synthesis of 2-(pentafluorophenyl)imidazolium (Suzuki-Miyaura coupling)

[0120] A magnetic stir bar was placed in a dry reaction flask, and the system was evacuated and purged with nitrogen three times to ensure an inert atmosphere. Then, 10.0 mmol of 2-bromoimidazole, 10.0 mmol of pentafluorophenylboronic acid, and 0.3 mmol of tetra(triphenylphosphine)palladium were added sequentially. 50 mL of degassed 1,4-dioxane and 20 mL of 2M sodium carbonate aqueous solution were injected sequentially using a syringe. The mixture was heated to 100 °C and refluxed under nitrogen protection with vigorous stirring for 30 h. After the reaction was completed, the mixture was cooled to room temperature, poured into ice water, and extracted with ethyl acetate (3 × 50 mL). The organic phases were combined, washed sequentially with saturated brine, dried over anhydrous Na2SO4, filtered, and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (petroleum ether / ethyl acetate 2:1, v / v). The target component was collected, and the solvent was evaporated to obtain a white solid product, 2-(pentafluorophenyl)imidazole.

[0121] (4) Epitaxial growth of hydrophobic ZIF-8 shell

[0122] 3.0 mmol of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 0.8 mmol of 2-(pentafluorophenyl)imidazole were dissolved in 80 mL of anhydrous methanol to obtain a metal mixed solution; 15 mmol of 2-methylimidazole (2-MIM) was dissolved in 40 mL of anhydrous methanol to obtain a 2-methylimidazole solution. The MIL-100(Fe)@PDA powder prepared in step (2) was dispersed in the metal mixed solution and ultrasonically treated for 30 min to allow Zn to precipitate. 2+ After being fully adsorbed onto the PDA, the 2-methylimidazole solution was quickly poured into the above mixed solution, stirred at room temperature for 4 hours, centrifuged to collect the final product and washed three times with anhydrous methanol, and finally placed at 70℃ for vacuum drying for 10 hours to obtain the MOF-based gas adsorbent, named MIL-100(Fe)@PDA@ZIF-8.

[0123] Using the intermediate products (e.g., D-UiO-66, D-UiO-66@PDA) and the final product (D-UiO-66@PDA@ZIF-8) from Examples 1-6 as samples, the following structural characterization and performance tests were performed:

[0124] (1) X-ray diffractometer (XRD)

[0125] Using D-UiO-66, D-UiO-66@PDA, and D-UiO-66@PDA@ZIF-8 from Example 1 as samples, their diffraction patterns were analyzed using a Bruker D8 Advance X-ray diffractometer (Germany), with a scanning range of 2-50°, a scanning speed of 10° / min, and a step size of 0.05°. The phase composition, crystallinity, and other relevant information were obtained. The results are as follows: Figure 1 As shown.

[0126] Figure 1XRD characterization results showed that D-UiO-66, D-UiO-66@PDA, and D-UiO-66@PDA@ZIF-8 all exhibited clear and sharp characteristic peaks within the characteristic diffraction range of 2θ = 7.1, 8.2, 17.1, and 27.6°, and the diffraction angles of each characteristic peak did not show significant shifts. This directly proves that D-UiO-66 itself maintains the typical complete crystal structure of UiO-66 material, and that the lattice collapse or structural damage was not caused by the introduction of defects. More importantly, it confirms that D-UiO-66, as a core material, maintains a stable crystal structure throughout the subsequent two modification steps. The reaction conditions in the entire preparation process did not damage the lattice integrity of the D-UiO-66 core, and no lattice interference or structural reconstruction occurred between the core and shell layers. Further observation of the XRD pattern of D-UiO-66@PDA@ZIF-8 reveals that, in addition to the characteristic peaks of D-Ui-O-66, the composite material also clearly exhibits characteristic diffraction peaks belonging to ZIF-8 material at 2θ=7.3, 10.3, 12.7, 14.6, 16.4, and 17.9°, indicating that the ZIF-8 shell has successfully crystallized and grown on the surface of D-UiO-66@PDA. Simultaneously, no new impurity peaks were detected in the entire XRD pattern. This result further confirms that during the preparation of D-UiO-66@PDA@ZIF-8, only physical coating and interfacial bonding occurred between the core layer (D-UiO-66), the intermediate layer (PDA), and the hydrophobic shell layer (ZIF-8), without any chemical reactions that would destroy their respective crystal structures. Ultimately, the composite material retains the structural integrity of each component.

[0127] (2) Specific surface area and pore size test analysis

[0128] Using the MOF-based gas adsorbents prepared in Examples 1-6 as samples, the BET surface area and pore structure of the materials were tested using a Belserp MAX II analyzer with N2 adsorption and desorption at -195°C. The total surface area was determined using the Brunol-Emmett-Taylor (BET) equation. The test results are as follows: Figure 2 and Figure 3 As shown.

[0129] BET test results show that the MOF-based gas adsorbents prepared in Examples 1-6 all have high specific surface areas, which are 1602 m² and 1602 m², respectively. 2 / g, 1550m 2 / g、1318m 2 / g、1743m 2 / g、1631m 2 / g、1513m 2 / g, exhibiting typical porous material structural characteristics. Further data analysis revealed a clear variation pattern in the specific surface area of ​​the MOF-based gas adsorbent: with the increase of dopamine hydrochloride concentration, due to the dense polymer film of the PDA layer itself, it physically covers part of the original porous structure and active sites on the surface of the D-UiO-66 core and MIL-100(Fe) core, blocking some micropores or mesoporous channels on the surface of the core material. This weakens the specific surface area contribution of the D-UiO-66 core and MIL-100(Fe), resulting in a significant decrease in the overall specific surface area of ​​the composite material.

[0130] It is worth noting that although the PDA coating layer leads to a loss of specific surface area, the final composite material still maintains a high specific surface area. This is due to the "compensation effect" of the hydrophobic ZIF-8 shell: as a typical porous material, hydrophobic ZIF-8 itself has an extremely high specific surface area and abundant microporous structure. When the hydrophobic ZIF-8 shell is grown on the surface of D-UiO-66@PDA and MIL-100(Fe)@PDA, the hydrophobic ZIF-8 will form a continuous and porous shell structure through in-situ crystallization, providing a large number of new surface sites and pore channels for the composite material. These additional specific surface areas can effectively offset some of the specific surface area loss caused by the PDA coating, so that the composite material can maintain a high specific surface area level while taking into account the integrity of the core and shell structure.

[0131] like Figure 3As shown, the composite materials prepared in Examples 1-3 all exhibit a typical "three-pore size" distribution characteristic. Among them, the ZIF-8 structure, as the hydrophobic shell, exhibits extremely high pore size uniformity, with its characteristic micropore size remaining stable at around 0.34 nm. This further confirms that the hydrophobic ZIF-8 shell maintains its unique SOD topology and regular microporous system in the composite material, without significant pore size distortion due to the interface interaction with the core layer and intermediate layer. The D-UiO-66 structure, as the core layer, mainly exhibits two characteristic pore size sizes, namely 1.1 nm and 2.4 nm. These two pore sizes correspond to two typical types of pores formed by defects in the D-UiO-66 material—the 1.1 nm micropores originate from the octahedral cage structure of the UiO-66 crystal itself after moderate pore expansion through defect control, while the 2.4 nm mesopores come from intergranular pores or grain stacking pores induced by defects. Together, they constitute the porous framework of the D-UiO-66 core layer. It is noteworthy that while the overall trend of these two characteristic pore sizes in the D-UiO-66 core layer is consistent across different embodiments, subtle differences still exist locally. Specifically, in some embodiments, the pore volume ratios of ~1.1 nm and ~2.4 nm pore sizes fluctuate, and the pore size of some samples shows a slight narrowing. The core reason for this difference lies in the regulatory effect of the PDA (polydopamine) deposition process on the porosity of the D-UiO-66 surface. Examples 4-6 also exhibit a "three-pore size" distribution characteristic, with pore sizes of 0.34 nm, 0.8 nm, and 3.0 nm, respectively.

[0132] (3) Contact angle test analysis

[0133] Using the MOF-based gas adsorbents prepared in Examples 1-6 as samples, the water contact angle of the materials was measured using a contact angle meter (Esr-N, Germany) to determine the affinity of the samples for water. Solid samples were pressed into thin sheets using a tablet press, and liquid was evenly coated onto a glass slide, which was then placed on the sample stage, and the stage was adjusted to a suitable height. The hydrophobicity of the material surface can be categorized as hydrophilic (CA < 90º) and hydrophobic (CA > 90º); the larger the contact angle, the stronger the hydrophobicity. The test results are as follows: Figure 4 As shown, a is the water contact angle of the MOF-based gas adsorbent prepared in Example 1, b is the water contact angle of the MOF-based gas adsorbent prepared in Example 2, c is the water contact angle of the MOF-based gas adsorbent prepared in Example 3, d is the water contact angle of the MOF-based gas adsorbent prepared in Example 4, e is the water contact angle of the MOF-based gas adsorbent prepared in Example 5, and f is the water contact angle of the MOF-based gas adsorbent prepared in Example 6.

[0134] The water contact angle test results show that the contact angles (123°, 119°, 122°, 115°, 117°, and 114°) of the MOF-based gas adsorbents prepared in Examples 1 to 6 are all greater than 90°. This indicates that the prepared composite material surfaces all have clear and stable hydrophobic properties, ensuring the structural integrity and long-term stability of the composite material under humid conditions. More importantly, the hydrophobic surface can reduce the competitive adsorption of water molecules and toluene molecules at the adsorption sites, thereby improving the adsorption selectivity and adsorption kinetic efficiency of the composite material for toluene.

[0135] (4) Dynamic adsorption performance test

[0136] Using the MOF-based gas adsorbents prepared in Examples 1-6 as samples, toluene adsorption tests were conducted on the materials using a UTEST static adsorption apparatus. Initial efficiency: test airflow (12 L / min), test resistance (100 Pa), and test concentration (600 ppb) were controlled; Poison capacity: test airflow (12 L / min), test resistance (100 Pa), and test concentration (10 ppm) were controlled. The adsorption capacity was calculated using the integral of the breakthrough curve, as shown in the following formula:

[0137]

[0138] In the formula, q (g / g) is the maximum adsorption capacity, F (mL / min) is the total gas flow rate, and C0 and C (mg / m³) are also present. 3 The inlet and outlet concentrations of toluene are denoted as m(g) and t(t), respectively. s (min) represents the adsorption time. Test results are as follows: Figure 5 and Figure 6 As shown.

[0139] Figure 5 The results show that, from the perspective of adsorption kinetics, the MOF-based gas adsorbents prepared in Examples 1-6 all exhibited a trend of "first increasing and then decreasing" in toluene adsorption breakthrough time: Initially, as the concentration of dopamine hydrochloride increased, the PDA intermediate layer gradually became denser, the pore connectivity and surface hydrophobicity improved simultaneously, the toluene diffusion resistance decreased, the adsorption rate constant increased, and the adsorption breakthrough time gradually increased; when the optimal matching was reached, the breakthrough time reached its peak, the core-shell-shell three-level pore structure achieved molecular-level synergy, the toluene mass transfer path was the shortest, the active site utilization rate was the highest, and the breakthrough time reached its peak; subsequently, as the process parameters continued to be adjusted, the PDA layer became excessively thickened, some micropores were blocked, the effective specific surface area and the number of accessible sites decreased, the mass transfer resistance exceeded the adsorption gain, resulting in a gradual decrease in breakthrough time.

[0140] Figure 6The results show that, in terms of adsorption capacity, the MOF-based gas adsorbents prepared in Examples 1-6 have adsorption capacities for toluene of 398 mg / g, 483 mg / g, 407 mg / g, 645 mg / g, 732 mg / g, and 657 mg / g, respectively, generally exhibiting a "first increase, then decrease" pattern consistent with the breakthrough time. However, Examples 4-6 have higher toluene adsorption capacities, mainly due to the higher specific surface area and pore volume of MIL-100(Fe).

[0141] To evaluate the practical application potential of the composite MOF materials from Examples 3 and 5, toluene adsorption-desorption cycle tests were further conducted to verify their reusability. The cycle tests were as follows: Figure 7 As shown, the results indicate that after five adsorption-desorption cycles, the toluene adsorption capacity remained at 450 mg / g and 655 mg / g, with a decrease rate of 6.8% and 10.5% compared to the initial adsorption amount. This demonstrates that the material still possesses stable adsorption kinetic efficiency after multiple cycles, fully confirming that the composite MOF has excellent reusability. Among them, Example 2 exhibits even better reusability.

[0142] To further verify the applicability of the MOF-based gas adsorbent of this application to toluene adsorption under actual complex working conditions, Examples 1-6 were placed in environments with RH=50% and 75% respectively to conduct toluene adsorption performance tests. Figure 8 As shown in the figure. Experimental results show that compared with the adsorption performance under normal temperature and humidity conditions, the adsorption capacity of each group of materials decreased to varying degrees. Among them, the adsorption capacity of toluene in Examples 1-3 remained at a high level under high humidity conditions, with the toluene adsorption capacity of Example 2 still reaching 468 mg / g. The adsorption capacity of Examples 4-6 decreased more significantly compared with Examples 1-3, and was significantly affected by humidity, but the adsorption capacity still reached 696 mg / g. This combination of high humidity stability and high selective adsorption performance makes this composite MOF material more suitable for the treatment of "moist toluene" in industrial waste gas, expanding its practical application scenarios.

[0143] The foregoing description includes examples from this specification. Of course, for the purposes of describing this specification, it is impossible to describe every conceivable combination of components or methods; however, those skilled in the art will understand that many other combinations and arrangements are possible. Therefore, this specification is intended to cover all such changes, modifications, and variations that fall within the spirit and scope of the appended claims. Furthermore, with regard to the use of the term "comprising" in the detailed description or claims, the term is intended to be inclusive in a manner similar to the term "including," as interpreted when "comprising" is used as a transitional word in the claims.

[0144] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention. Technical aspects, shapes, and structures not described in detail in this invention are all well-known technologies.

Claims

1. A MOF-based gas adsorbent with a core-shell structure, characterized in that, It includes an inner MOF core, a polydopamine intermediate layer, and a superhydrophobic modified ZIF-8 shell, from the inside out. The MOF core is defect-engineered UiO-66 or MIL-100(Fe).

2. The MOF-based gas adsorbent with a core-shell structure according to claim 1, wherein, The raw materials for preparing the MOF-based gas adsorbent include: zinc nitrate hexahydrate, 2-methylimidazole, 2-(pentafluorophenyl)imidazole, and polydopamine-encapsulated MOF core. The polydopamine-encapsulated MOF core is either D-UiO-66@PDA or MIL-100(Fe)@PDA. D-UiO-66@PDA is polydopamine-encapsulated defect-engineered UiO-66, and MIL-100(Fe)@PDA is polydopamine-encapsulated MIL-100(Fe).

3. The MOF-based gas adsorbent with a core-shell structure according to claim 2, wherein, The molar ratio of the MOF core encapsulated with zinc nitrate hexahydrate, 2-methylimidazole, 2-(pentafluorophenyl)imidazole and polydopamine is (2.0–4.0) mmol:(12.0–18.0) mmol:(0.6–0.9) mmol:(40–80) mg.

4. A method for preparing a MOF-based gas adsorbent with a core-shell structure, characterized in that, Includes the following steps: Weigh zinc nitrate hexahydrate and 2-(pentafluorophenyl)imidazole and add them to anhydrous methanol to obtain a mixed metal solution; weigh 2-methylimidazole and add it to anhydrous methanol to obtain a 2-methylimidazole solution; The dried polydopamine-encapsulated MOF core was dispersed in a metal mixed solution and ultrasonically treated for 20–40 min. Then, a 2-methylimidazole solution was added, and the mixture was stirred at room temperature for 3–5 h. The final product was collected by centrifugation and washed 3–5 times with anhydrous methanol. Finally, it was vacuum dried at 55–70 °C for 10–15 h to obtain the MOF-based gas adsorbent. The polydopamine-encapsulated MOF core was D-UiO-66@PDA or MIL-100(Fe)@PDA powder. D-UiO-66@PDA is polydopamine-encapsulated defect-engineered UiO-66, and MIL-100(Fe)@PDA is polydopamine-encapsulated MIL-100(Fe).

5. The preparation method according to claim 4, wherein, The molar ratio of zinc nitrate hexahydrate, 2-methylimidazole, 2-(pentafluorophenyl)imidazole and polydopamine encapsulating the MOF core is (2.0–4.0) mmol : (12.0–18.0) mmol : (0.6–0.9) mmol : (40–80) mg.

6. The preparation method according to claim 4, wherein, The method for preparing the defect-engineered UiO-66 is as follows: Zirconium oxychloride octahydrate and terephthalic acid were weighed and dissolved in N,N-dimethylformamide. The mixture was dissolved by sonication, and glacial acetic acid was added. The mixture was stirred continuously for 20–40 min and reacted at 120–150 °C for 24–48 h. The solid product was collected by centrifugation and washed 3–5 times with N,N-dimethylformamide and anhydrous ethanol, respectively. Finally, the product was dried under vacuum at 80–100 °C to obtain defect-engineered UiO-66.

7. The preparation method according to claim 4, wherein, The preparation method of MIL-100(Fe) is as follows: Weigh out ferric nitrate nonahydrate and dissolve it in deionized water to prepare a metal salt solution; weigh out pyromellitic acid and dissolve it in deionized water to prepare a ligand solution. With stirring, the ligand solution was added dropwise to the metal salt solution and reacted at 110–120 °C for 12–18 h. After cooling to room temperature, the product was washed 3–5 times by centrifugation with DMF and anhydrous ethanol, respectively. Finally, the solid product was dried under vacuum at 80–100 °C to obtain MIL-100(Fe).

8. The preparation method according to claim 4, wherein, The preparation method of the polydopamine-encapsulated MOF core is as follows: Tris(hydroxymethyl)aminomethane was added to Tris-HCl buffer solution to prepare a buffer mixture. Defect-engineered UiO-66 and MIL-100(Fe) powders were dispersed in the buffer mixture and sonicated for 20-40 min to disperse evenly. Then, dopamine hydrochloride was added and stirred at room temperature for 6-12 h. The precipitate was collected by centrifugation and washed 3-5 times with deionized water until the supernatant was colorless. Finally, the product was vacuum dried at 55-75℃ for 5-8 h.

9. The preparation method according to claim 4, wherein, The preparation method of the 2-(pentafluorophenyl)imidazole is as follows: Take a reaction vessel and add 2-bromoimidazole, pentafluorophenylboronic acid and tetra(triphenylphosphine)palladium sequentially under an inert atmosphere. Then, inject degassed 1,4-dioxane and sodium carbonate aqueous solution sequentially. Heat to 90-100℃ and stir under reflux for 24-36 hours under nitrogen protection. After cooling to room temperature, pour the reaction solution into ice water and extract with ethyl acetate. Combine the organic phases, wash with saturated brine, dry with anhydrous Na2SO4, filter and concentrate under reduced pressure. The crude product is purified by silica gel column chromatography. Collect the target component, evaporate the solvent to obtain the solid product 2-(pentafluorophenyl)imidazole.

10. The application of the MOF-based gas adsorbent according to any one of claims 1-3, or the MOF-based gas adsorbent prepared by the preparation method according to any one of claims 4-9, in toluene adsorption materials.

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