Heterometallic-organic framework confinement polyaniline composite adsorbent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of gas adsorption materials, in particular to a dissimilar metal-organic framework confinement polyaniline composite adsorbent and a preparation method and application thereof. The preparation method comprises the following steps: adopting chromium-copper dissimilar metal matching, and constructing a stable Lewis acid site in an MIL-101 skeleton; introducing a sulfonic acid group through a ligand exchange strategy, and establishing a Bronsted acid site; and finally, carrying out confinement polymerization on aniline in MOF pore channels to form rich hydrogen bond binding sites so as to obtain the dissimilar metal-organic framework confinement polyaniline composite adsorbent. According to the dissimilar metal-organic framework confined polyaniline composite adsorbent disclosed by the invention, through triple synergistic effects of dissimilar metal Lewis acid sites, sulfonic acid group Bronsted acid sites and polyaniline hydrogen bond sites, a multiple ammonia gas capture mechanism is constructed, and the adsorption efficiency and adsorption effect on ammonia gas are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of gas adsorption materials technology, and in particular to heterometallic-organic framework confined polyaniline composite adsorbents, their preparation methods and applications. Background Technology

[0002] In contemporary semiconductor manufacturing, as integrated circuit process nodes approach physical limits, the cleanliness requirements for wafer fabrication environments have expanded from traditional particulate matter control to the precise control of trace gaseous molecular contaminants. Ammonia (NH3), a typical alkaline contaminant, has a small molecular diameter, high polarity, and strong reactivity, posing increasingly prominent problems in advanced manufacturing processes. For example, in extreme ultraviolet lithography, ppb-level ammonia in the environment can interact with photochemical products, leading to irreversible chemical contamination on the surface of optical components; in atomic layer deposition, ammonia molecules compete for adsorption with metal-organic precursors, causing defects at the thin film growth interface, directly affecting the dielectric properties of the gate oxide layer and device reliability.

[0003] Currently, the industry mainly employs multi-stage filtration schemes to control gaseous molecular pollutants, with terminal chemical filters playing a crucial role. Existing adsorption material systems suffer from the following technical bottlenecks: Traditional activated carbon materials (such as those described in patent CN117942935A), while possessing a large specific surface area, exhibit heterogeneous surface chemical properties, resulting in limited specific adsorption capacity for ammonia. Furthermore, under fluctuating humidity conditions, water vapor and ammonia molecules exhibit significant competitive adsorption effects, leading to a sharp decline in adsorption efficiency under real-world operating conditions. Ion exchange resin materials (patent CN105174243B) achieve chemical adsorption of ammonia through the acid-base interaction of functional groups; however, their polymer backbone is typically amorphous, resulting in generally low effective specific surface areas and insufficient dynamic adsorption capacity for ultra-low concentrations of ammonia, making it difficult to meet the stringent requirements for filter lifespan during long-term continuous operation in semiconductor plants.

[0004] Metal-organic frameworks (MOFs), with their highly ordered crystal structures and precisely designable pore environments, offer a novel pathway for the development of next-generation chemical filters. Previous studies have confirmed that certain MOFs containing open metal sites exhibit excellent adsorption performance for ammonia; however, these materials still face significant challenges in practical applications. Most MOFs exhibit poor water stability, and in high-humidity environments, metal-ligand bonds are prone to hydrolysis, leading to framework degradation. Furthermore, single-type adsorption sites are insufficient for achieving efficient and persistent ammonia molecule capture in complex gaseous environments.

[0005] Therefore, developing a novel adsorbent material that combines high specific surface area, multiple adsorption sites, and excellent chemical stability has become an urgent need to solve the problem of ammonia pollution control in advanced semiconductor manufacturing. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a heterometallic-organic framework confined polyaniline composite adsorbent, its preparation method and application, so as to at least solve the problem that ammonia adsorbent materials with a single type of adsorption site are difficult to achieve efficient and persistent capture of ammonia molecules in complex gas phase environments.

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

[0008] This invention provides a method for preparing a heterometallic-organic framework confined polyaniline composite adsorbent. The method involves using a chromium-copper heterometallic pair to construct stable Lewis acid sites in the MIL-101 framework; then introducing sulfonic acid groups through a ligand exchange strategy to establish Brønsted acid sites; and finally confining and polymerizing aniline within the MOF channels to form abundant hydrogen bonding sites, thereby obtaining the heterometallic-organic framework confined polyaniline composite adsorbent.

[0009] Furthermore, the preparation method includes the following steps:

[0010] To prepare the precursor solution, weigh out the chromium source and copper source and add them to the solvent, then add terephthalic acid and stir at room temperature for 30-60 minutes to obtain the precursor solution.

[0011] A heterometallic MOF with Lewis acid sites was synthesized by transferring the precursor solution to a high-pressure reactor and reacting it at 200–220 °C for 5–24 h. The mixture was then naturally cooled to room temperature, and the solid product was collected by centrifugation. The solid product was washed three times each with DMF, 1–5% ammonium fluoride solution, and deionized water at 60–80 °C. The washed solid product was then placed in a vacuum drying oven and activated at 120–150 °C for 4–8 h to obtain the heterometallic MOF framework with Lewis acid sites.

[0012] Brønsted acid sites were constructed by dispersing a heterometallic MOF framework in deionized water, adding monosodium 2-sulfonic acid terephthalate, and then heating to 70–90 °C and stirring under reflux for 12–36 h. After the reaction was completed, the product obtained by centrifugation was repeatedly washed with DMF and deionized water at 60–80 °C until the filtrate was neutral and colorless. Then, it was vacuum dried at 100–120 °C for 4–12 h to obtain the MIL-101-SO3H material.

[0013] A physical confinement process was employed to introduce polyaniline guests. MIL-101-SO3H material was dispersed in ice-cold deionized water at 0–5°C, followed by the addition of hydrochloric acid solution and ultrasonic treatment for 10–20 min to obtain a suspension. Then, under continuous stirring and an ice bath, freshly distilled aniline monomer was slowly added dropwise while stirring continued for 1–3 h. Ammonium persulfate was dissolved in ice-cold deionized water to obtain an APS solution. The APS solution was then added dropwise to the suspension at 0–5°C to initiate a polymerization reaction. After the addition was complete, the reaction continued in an ice bath for 12–24 h. The precipitate obtained by centrifugation was washed repeatedly with deionized water and ethanol until the filtrate was colorless. Finally, the precipitate was dried in a vacuum environment at 50–80°C for 6–12 h to obtain a heterometallic-organic framework confined polyaniline composite adsorbent.

[0014] Another aspect of the present invention provides a heterometallic-organic framework confined polyaniline composite adsorbent, which is prepared by the aforementioned preparation method.

[0015] Another aspect of the present invention provides the application of the above-mentioned heterometallic-organic framework confined polyaniline composite adsorbent in the preparation of ammonia adsorption materials.

[0016] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0017] (1) A significant improvement in ammonia adsorption capacity was achieved. A multi-layered ammonia capture mechanism was constructed through the triple synergistic effect of heterometallic Lewis acid sites, sulfonic acid Brønsted acid sites, and polyaniline hydrogen bonding sites. Performance test data showed that the heterometallic-organic framework confined polyaniline composite adsorbent prepared under optimal conditions had a mass adsorption ratio of up to 604 mg / g for ammonia, which was much higher than that of the control sample without polyaniline guest (adsorption ratio <400 mg / g), thus solving the technical problem of insufficient adsorption capacity of traditional single-functional materials.

[0018] (2) It maintains excellent adsorption kinetic performance. Although the introduction of polyaniline reduces the specific surface area of ​​the material (from 2641 m² / g to about 2530 m² / g), the inherent hierarchical pore structure of the heterometallic MOF provides a fast diffusion path for ammonia molecules, ensuring that the material still has a fast adsorption rate in the early stage of adsorption, thus achieving a balance between high capacity and fast response.

[0019] (3) A controllable material design strategy has been established. By adjusting the ratio of dissimilar metals, the amount of sulfonic acid groups introduced and the amount of polyaniline loading, the pore environment and surface chemical properties of the material can be precisely controlled, so as to achieve adaptive design for different concentrations of ammonia and different environmental conditions, providing a flexible and controllable technical path for the development of a series of ammonia adsorption materials. Attached Figure Description

[0020] Figure 1 These are the XRD patterns of the final products of Examples 1 / 2 / 3 and Comparative Example 1 / 2;

[0021] Figure 2 The nitrogen adsorption-desorption curve of MIL-101(Cr / Cu)-SO3H@PANI-1 in Example 1 is shown.

[0022] Figure 3 The nitrogen adsorption-desorption curve of MIL-101(Cr / Cu)-SO3H@PANI-2 in Example 2 is shown.

[0023] Figure 4 The nitrogen adsorption-desorption curve of MIL-101(Cr / Cu)-SO3H@PANI-3 in Example 3 is shown.

[0024] Figure 5 The nitrogen adsorption-desorption curves of MIL-101(Cr)@PANI in Comparative Example 1 are shown.

[0025] Figure 6 The nitrogen adsorption-desorption curves of MIL-101(Cr / Cu)-SO3H in Comparative Example 2 are shown.

[0026] Figure 7 These are the dynamic adsorption curves of NH3 for the final products of Examples 1 / 2 / 3 and Comparative Example 1 / 2;

[0027] Figure 8 The mass adsorption ratio of NH3 by the final products of Examples 1 / 2 / 3 and Comparative Example 1 / 2 is given. Detailed Implementation

[0028] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0029] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0030] The method for preparing the heterometallic-organic framework confined polyaniline composite adsorbent disclosed in this application achieves a technological breakthrough by constructing a composite system with multiple adsorption sites: First, a chromium-copper heterometallic pair is used to construct stable Lewis acid sites in the MIL-101 framework; then, sulfonic acid groups are introduced through a ligand exchange strategy to establish Brønsted acid sites; finally, aniline is confined and polymerized within the MOF channels to form abundant hydrogen bonding sites. This synergistic mechanism of triple adsorption sites enables the material to exhibit extremely strong capture ability for ammonia molecules.

[0031] Specifically, the preparation method of the heterometallic-organic framework confined polyaniline composite adsorbent includes the following steps:

[0032] (a) Preparation of precursor solution

[0033] The molar ratio of chromium in the chromium source to copper in the copper source is (5-10):1 to ensure that copper ions can be effectively doped without destroying the crystal structure of the target MOF. The molar ratio of terephthalic acid to the total molar ratio of chromium and copper is (1-1.5):1. Chromium nitrate nonahydrate (Cr(NO3)3·9H2O), copper nitrate triahydrate (Cu(NO3)2·3H2O), and terephthalic acid are accurately weighed respectively.

[0034] Chromium and copper sources were added to a solvent, followed by terephthalic acid (H2BDC) as the main ligand. To promote crystal growth, a mineralizing agent was added. The mixture was then magnetically stirred at room temperature for 30–60 minutes until a homogeneous mixed solution was formed, thus obtaining the precursor solution.

[0035] In this step, the solvent is an aqueous solution containing 0-20% by volume N,N-dimethylformamide, and the mineralizing agent is a mixture of concentrated nitric acid and glacial acetic acid in a volume ratio of 1:(50-100).

[0036] A mineralizing agent containing concentrated nitric acid and glacial acetic acid provides an appropriate amount of H₂. + The system pH can be adjusted to inhibit the hydrolysis and precipitation of metal ions, while regulating the deprotonation rate of ligands to allow crystals to grow slowly and form MOF particles with uniform size and high crystallinity. Glacial acetic acid can also be used as a structure directing agent to induce the growth of characteristic crystal faces of MIL-101.

[0037] (II) Synthesis of heterometallic MOFs with Lewis acid sites

[0038] The precursor solution prepared in step (II) was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene, with the filling degree controlled at 50% to 70%. The reactor was sealed and placed in a forced-air drying oven, and reacted at 200 to 220°C for 5 to 24 hours. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The green solid product was collected by centrifugation and washed three times in sequence with DMF, 1 to 5% ammonium fluoride solution and deionized water at 60 to 80°C. The washed solid product was placed in a vacuum drying oven and activated at 120 to 150°C for 4 to 8 hours to obtain a porous MIL-101(Cr / Cu) framework with high specific surface area and abundant Lewis acid sites, i.e., a heterometallic MOF framework.

[0039] (III) Construction of Brønsted acid sites

[0040] A heterometallic MOF framework was dispersed in deionized water, and an excess (preferably 2–10 times molar excess compared to the theoretical ligand sites in the MOF) of 2-sulfonic acid monosodium terephthalate (H2BDC-SO3Na) was added as an exchange ligand. The mixture was then heated to 70–90 °C and refluxed with magnetic stirring for 12–36 h to allow the sulfonic acid-functionalized ligands to diffuse fully into the MOF framework and complete the exchange. After the reaction, the product obtained by centrifugation was repeatedly washed with DMF and deionized water at 60–80 °C until the filtrate was neutral and colorless, ensuring the removal of physically adsorbed exchange ligands. Subsequently, the product was vacuum dried at 100–120 °C for 4–12 h to obtain the MIL-101(Cr / Cu)-SO3H material.

[0041] In this step, the mass ratio of 2-sulfonic acid monosodium terephthalate to the heterometallic MOF framework is (2-3):1.

[0042] The skeleton of MIL-101 (Cr / Cu) possesses ligand exchangeability, which is a core prerequisite for ligand exchange. The carboxyl group of the 2-sulfonic acid monosodium terephthalate (H2BDC−SO3Na) undergoes a coordination substitution reaction with uncoordinated or weakly coordinated H2BDC ligands in the MOF skeleton. The principle is that the sulfonic acid-modified ligand has a stronger coordination ability with metal ions than the unmodified H2BDC, and can replace the original ligand through a "dissolution-recognition" process.

[0043] (iv) Physical confinement to introduce polyaniline guest

[0044] Disperse 50–100 mg of MIL-101(Cr / Cu)-SO3H material in 10–30 ml of ice-cold deionized water at 0–5 °C, then add 0.05 mol / L hydrochloric acid solution and sonicate for 10–20 min to obtain a suspension. Then, under continuous stirring and an ice bath, slowly add freshly distilled aniline monomer, continuing stirring for 1–3 h to allow the aniline monomer to fully adsorb and diffuse into the mesoporous cages of the MOF. Dissolve ammonium persulfate in ice-cold deionized water to obtain an APS solution. At 0–5 °C, use a dropping funnel to add the APS solution dropwise to the suspension to initiate the polymerization reaction. After the addition is complete, continue the reaction in an ice bath for 12–24 h. Observe that the system color gradually turns dark green, indicating successful polyaniline formation. After the reaction is complete, centrifuge the final product to obtain a precipitate, then wash repeatedly with deionized water and ethanol until the filtrate is colorless to completely remove the polyaniline polymerized on the outside of the MOF particles. Then, it is dried in a vacuum environment at 50-80℃ for 6-12 hours to obtain a heterometallic-organic framework confined polyaniline composite adsorbent, denoted as MIL-101(Cr / Cu)-SO3H@PANI.

[0045] In this step, the mass-to-volume ratio of MIL-101-SO3H material to hydrochloric acid solution is 1000 mg: 1 mL, the mass-to-volume ratio of MIL-101-SO3H material to aniline monomer is 1000 mg: (1-5) mL, and the molar ratio of ammonium persulfate to aniline monomer is (1-1.2): 1.

[0046] MIL-101(Cr / Cu)-SO3H possesses a rich mesoporous cage structure. Under ice bath (°C) and hydrochloric acid acidification conditions, aniline monomers can enter the interior of the MOF cages through adsorption and diffusion within the pores. The role of the low-temperature environment is to reduce the polymerization rate of aniline monomers, allowing them to diffuse sufficiently into the pores rather than rapidly polymerizing on the MOF surface. Ammonium persulfate (APS) acts as an oxidant, slowly oxidizing the aniline monomers at low temperatures, initiating a free radical polymerization reaction. Because the polymerization reaction is confined within the MOF cages, the growth of polyaniline is constrained by the pore size, forming nanoscale polyaniline particles and avoiding macroscopic agglomeration. Polyaniline and the MOF framework are combined through electrostatic interactions and pore confinement effects to form the MIL-101(Cr / Cu)-SO3H@PANI composite material.

[0047] The following examples 1-5 will provide a detailed description of the heterometallic-organic framework confined polyaniline composite adsorbent and its preparation method of this application:

[0048] Example 1

[0049] The preparation method of the heterometallic-organic framework confined polyaniline composite adsorbent in this embodiment is as follows:

[0050] (a) Preparation of precursor solution

[0051] Accurately weigh 5 mmol Cr(NO3)3·9H2O, 1 mmol Cu(NO3)2·3H2O, and 7.2 mmol terephthalic acid. Dissolve Cr(NO3)3·9H2O and Cu(NO3)2·3H2O together in 30 mL of 10% N,N-dimethylformamide aqueous solution, then add terephthalic acid. To promote crystal growth, add 0.03 mL concentrated nitric acid and 3 mL glacial acetic acid as mineralizing agents. Stir magnetically at room temperature for 30 min until a homogeneous mixed solution is formed to obtain the precursor solution.

[0052] (II) Synthesis of heterometallic MOFs with Lewis acid sites

[0053] The precursor solution prepared in step (II) was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene, with the filling degree controlled at 70%. The reactor was sealed and placed in a forced-air drying oven, and reacted at 205℃ for 8 hours. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The green solid product was collected by centrifugation and washed three times each with DMF, 2% ammonium fluoride solution and deionized water at 80℃. The washed solid product was placed in a vacuum drying oven and activated at 120℃ for 8 hours to obtain a porous MIL-101(Cr / Cu) framework with high specific surface area and abundant Lewis acid sites.

[0054] (III) Construction of Brønsted acid sites

[0055] 200 mg of porous MIL-101(Cr / Cu) framework was dispersed in 30 mL of deionized water, and 500 g of 2-sulfonic acid monosodium terephthalate was added as an exchange ligand. The mixture was then heated to 80 °C and refluxed with magnetic stirring for 24 h. After the reaction was completed, the product obtained by centrifugation was repeatedly washed with DMF at 80 °C and deionized water until the filtrate was neutral and colorless, ensuring the removal of physically adsorbed exchange ligands. Subsequently, it was vacuum dried at 105 °C for 12 h to obtain the MIL-101(Cr / Cu)-SO3H material.

[0056] (iv) Physical confinement to introduce polyaniline guest

[0057] 100 mg of MIL-101(Cr / Cu)-SO3H material was dispersed in 30 mL of ice-cold deionized water at 2 °C. Then, 0.05 mol / L hydrochloric acid solution was added, and the mixture was sonicated for 10 min to obtain a suspension. Subsequently, under continuous stirring and an ice bath, 0.1 mL of freshly distilled aniline monomer was slowly added dropwise, and stirring was continued for 1.5 h to allow the aniline monomer to be fully adsorbed and diffused into the mesoporous cages of the MOF. 230 mg of ammonium persulfate was dissolved in 7.5 mL of ice-cold deionized water to obtain an APS solution. At 2 °C, the APS solution was added dropwise to the suspension using a dropping funnel to initiate the polymerization reaction. After the addition was complete, the reaction was continued in an ice bath for 16 h. The system color gradually turned dark green, indicating successful polyaniline formation. After the reaction, the final product was centrifuged, and the resulting precipitate was washed repeatedly with deionized water and ethanol until the filtrate was colorless to completely remove the polyaniline polymerized on the outside of the MOF particles. Then, it was dried in a vacuum environment at 80°C for 12 hours to obtain a heterometallic-organic framework confined polyaniline composite adsorbent, denoted as MIL-101(Cr / Cu)-SO3H@PANI-1.

[0058] Example 2

[0059] In step one of Example 1, the molar ratio of Cr(NO3)3·9H2O to Cu(NO3)2·3H2O was changed to 10:1, while other steps and conditions remained unchanged, to obtain MIL-101(Cr / Cu)-SO3H@PANI-2.

[0060] Example 3

[0061] In step four of Example 1, the amount of aniline monomer was changed to 1.5 ml, the amount of APS was changed to 345 mg, and other steps and conditions remained unchanged to obtain MIL-101(Cr / Cu)-SO3H@PANI-3.

[0062] Example 4

[0063] The preparation method of the heterometallic-organic framework confined polyaniline composite adsorbent in this embodiment is as follows:

[0064] (a) Preparation of precursor solution

[0065] Accurately weigh 6 mmol Cr(NO3)3·9H2O, 1 mmol Cu(NO3)2·3H2O, and 7.0 mmol terephthalic acid. Dissolve Cr(NO3)3·9H2O and Cu(NO3)2·3H2O together in 40 mL of deionized water, then add terephthalic acid. To promote crystal growth, add 0.05 mL concentrated nitric acid and 2.5 mL glacial acetic acid as mineralizing agents. Stir magnetically at room temperature for 40 min until a homogeneous mixed solution is formed, thus obtaining the precursor solution.

[0066] (II) Synthesis of heterometallic MOFs with Lewis acid sites

[0067] The precursor solution prepared in step (II) was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene, with the filling degree controlled at 50%. The reactor was sealed and placed in a forced-air drying oven, and reacted at 200℃ for 24h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The green solid product was collected by centrifugation and washed three times each with DMF, 1% ammonium fluoride solution and deionized water at 60℃. The washed solid product was placed in a vacuum drying oven and activated at 130℃ for 5h to obtain a porous MIL-101(Cr / Cu) framework with high specific surface area and abundant Lewis acid sites.

[0068] (III) Construction of Brønsted acid sites

[0069] 200 mg of porous MIL-101(Cr / Cu) framework was dispersed in 30 mL of deionized water, and 400 g of 2-sulfonic acid monosodium terephthalate was added as an exchange ligand. The mixture was then heated to 70 °C and refluxed with magnetic stirring for 36 h. After the reaction was completed, the product obtained by centrifugation was repeatedly washed with DMF at 75 °C and deionized water until the filtrate was neutral and colorless, ensuring the removal of physically adsorbed exchange ligands. Subsequently, it was vacuum dried at 100 °C for 10 h to obtain the MIL-101(Cr / Cu)-SO3H material.

[0070] (iv) Physical confinement to introduce polyaniline guest

[0071] 100 mg of MIL-101(Cr / Cu)-SO3H material was dispersed in 10 mL of ice-cold deionized water at 0 °C. Then, 0.1 mL of 0.05 mol / L hydrochloric acid solution was added, and the mixture was sonicated for 15 min to obtain a suspension. Subsequently, under continuous stirring and an ice bath, 0.11 mL of freshly distilled aniline monomer was slowly added dropwise, and stirring was continued for 1 h to allow the aniline monomer to be fully adsorbed and diffused into the mesoporous cages of the MOF. 230 mg of ammonium persulfate was dissolved in 7.5 mL of ice-cold deionized water to obtain an APS solution. Under 0 °C, the APS solution was added dropwise to the suspension using a dropping funnel to initiate the polymerization reaction. After the addition was complete, the reaction was continued in an ice bath for 24 h. The system color gradually turned dark green, indicating successful polyaniline formation. After the reaction, the final product was centrifuged, and the resulting precipitate was washed repeatedly with deionized water and ethanol until the filtrate was colorless to completely remove the polyaniline polymerized on the outside of the MOF particles. Then, it was dried in a vacuum environment at 50°C for 8 hours to obtain a heterometallic-organic framework confined polyaniline composite adsorbent, denoted as MIL-101(Cr / Cu)-SO3H@PANI-4.

[0072] Example 5

[0073] The preparation method of the heterometallic-organic framework confined polyaniline composite adsorbent in this embodiment is as follows:

[0074] (a) Preparation of precursor solution

[0075] Accurately weigh 8 mmol Cr(NO3)3·9H2O, 1 mmol Cu(NO3)2·3H2O, and 13.5 mmol terephthalic acid. Dissolve Cr(NO3)3·9H2O and Cu(NO3)2·3H2O together in 50 mL of 20% N,N-dimethylformamide aqueous solution, then add terephthalic acid. To promote crystal growth, add 0.05 mL concentrated nitric acid and 4 mL glacial acetic acid as mineralizing agents. Stir magnetically at room temperature for 60 min until a homogeneous mixed solution is formed to obtain the precursor solution.

[0076] (II) Synthesis of heterometallic MOFs with Lewis acid sites

[0077] The precursor solution prepared in step (II) was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene, with the filling degree controlled at 60%. The reactor was sealed and placed in a forced-air drying oven, and reacted at 220°C for 5 hours. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The green solid product was collected by centrifugation and washed three times each with DMF, 5% ammonium fluoride solution and deionized water at 70°C. The washed solid product was placed in a vacuum drying oven and activated at 150°C for 4 hours to obtain a porous MIL-101(Cr / Cu) framework with high specific surface area and abundant Lewis acid sites.

[0078] (III) Construction of Brønsted acid sites

[0079] 200 mg of porous MIL-101(Cr / Cu) framework was dispersed in 30 mL of deionized water, and 600 g of 2-sulfonic acid monosodium terephthalate was added as an exchange ligand. The mixture was then heated to 90 °C and refluxed with magnetic stirring for 12 h. After the reaction was completed, the product obtained by centrifugation was repeatedly washed with DMF at 60 °C and deionized water until the filtrate was neutral and colorless, ensuring the removal of physically adsorbed exchange ligands. Subsequently, it was vacuum dried at 120 °C for 4 h to obtain the MIL-101(Cr / Cu)-SO3H material.

[0080] (iv) Physical confinement to introduce polyaniline guest

[0081] 100 mg of MIL-101(Cr / Cu)-SO3H material was dispersed in 25 mL of ice-cold deionized water at 5 °C. 0.1 mL of 0.05 mol / L hydrochloric acid solution was added, and the mixture was sonicated for 20 min to obtain a suspension. Then, under continuous stirring and an ice bath, 0.12 mL of freshly distilled aniline monomer was slowly added dropwise, and stirring continued for 3 h to allow the aniline monomer to be fully adsorbed and diffused into the mesoporous cages of the MOF. 230 mg of ammonium persulfate was dissolved in 7.5 mL of ice-cold deionized water to obtain an APS solution. At 5 °C, the APS solution was added dropwise to the suspension using a dropping funnel to initiate the polymerization reaction. After the addition was complete, the reaction was continued in an ice bath for 12 h. The system color gradually turned dark green, indicating successful polyaniline formation. After the reaction, the final product was centrifuged, and the resulting precipitate was washed repeatedly with deionized water and ethanol until the filtrate was colorless to completely remove the polyaniline polymerized on the outside of the MOF particles. Then, it was dried in a vacuum environment at 80°C for 6 hours to obtain a heterometallic-organic framework confined polyaniline composite adsorbent, denoted as MIL-101(Cr / Cu)-SO3H@PANI-5.

[0082] Comparative Example 1

[0083] In Example 1, the molar ratio of Cr(NO3)3·9H2O to Cu(NO3)2·3H2O in step (i) was changed to 1:0, step (ii) was removed, and other steps and conditions remained unchanged to obtain MIL-101(Cr)@PANI.

[0084] Comparative Example 2

[0085] Remove step (iv) from Example 1, while keeping other steps and conditions unchanged, to obtain MIL-101(Cr / Cu)-SO3H.

[0086] The heterometallic-organic framework confined polyaniline composite adsorbents prepared in Examples 1-3 were used as samples for performance testing:

[0087] (1) X-ray diffraction analysis

[0088] This application uses a Bruker D8 Advance X-ray diffractometer (Germany) for testing. The scanning range is set to 2-50°, the scanning speed is 10° / min, and the step size is 0.05°. Samples from Examples 1 / 2 / 3 and Comparative Example 1 / 2 are tested. The results are as follows: Figure 1 As shown.

[0089] like Figure 1 As shown in the XRD patterns, all samples exhibited similarities to the simulated spectra. Figure 1The characteristic diffraction peaks of MIL-101(Cr) indicate that its basic crystal framework was maintained during the introduction of copper ions, ligand exchange, and subsequent processing. Notably, the diffraction peak intensity of MIL-101(Cr / Cu)-SO3H@PANI-3 decreased significantly at small angles, and two unknown peaks appeared in the 25°-30° range, suggesting that excessive guest introduction may have a subtle impact on the crystallinity of the MOF or its interaction with PANI. In summary, the XRD data strongly support the successful synthesis of the heterometallic MOF framework, sulfonic acid functionalization, and the effective confined introduction of the polyaniline guest, providing a structural basis for achieving efficient ammonia adsorption.

[0090] (2) Specific surface area test analysis

[0091] Using a Bioder SSA-6000 surface area analyzer at -196°C liquid nitrogen temperature, the adsorption and desorption isotherms of nitrogen on the material were precisely measured. The specific surface area was calculated using the Brunauer-Emmett-Teller (BET) model, and the pore size distribution and pore volume were analyzed using the Barrett-Joyner-Halenda (BJH) method, thus comprehensively characterizing the porosity properties of the material. The test results are as follows: Figure 2-6 As shown.

[0092] Figure 2-6 The data results show that the BET specific surface areas of the samples prepared in Examples 1, 2, 3, and Comparative Example 1 are similar, approximately 2528 m² / g, 2535 m² / g, 2530 m² / g, and 2530 m² / g, respectively. This indicates that under different Cr / Cu molar ratios (Examples 1 and 2) or different amounts of aniline monomer (Examples 1 and 3), the final composite materials all maintain similar pore structures. However, the BET specific surface area of ​​Comparative Example 2 (MIL-101(Cr / Cu)-SO3H) is significantly higher than that of the other samples, reaching 2641 m² / g. This is because this sample did not undergo the fourth step of introducing the polyaniline guest. Polyaniline polymer chains occupy a large amount of mesoporous cage space inside the MIL-101(Cr / Cu)-SO3H material, which directly leads to a decrease in the overall specific surface area of ​​the composite material. In other words, the significant and consistent reduction in specific surface area of ​​Examples 1-3 and Comparative Example 1 is direct physical evidence that polyaniline has successfully filled into the MOF channels and formed a host-guest composite structure.

[0093] (3) Dynamic adsorption performance test of ammonia

[0094] NH3 adsorption tests were conducted on the material using a UTEST static adsorption apparatus. Initial efficiency: test airflow (12 L / min), test resistance (100 Pa), test concentration (600 ppb); Poisoning capacity: test airflow (15 L / min), test resistance (100 Pa), test concentration (10 ppm). The adsorption capacity was calculated using the integral of the breakthrough curve, as shown in the following formula:

[0095]

[0096] Where 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. The final test results are as follows: Figure 7 and Figure 8 As shown.

[0097] Combination Figure 7 and Figure 8 The data show that the NH3 adsorption breakthrough time of the three groups of samples in Examples 2, 1, and 3 was successively delayed, and the mass adsorption ratios of NH3 reached 537 mg / g, 457 mg / g, and 604 mg / g, respectively, all of which were much higher than those of Comparative Example 1 (MIL-101(Cr)@PANI) and Comparative Example 2 (MIL-101(Cr / Cu)-SO3H). Among them, Example 3, due to the introduction of a higher content of polyaniline guest, provided a denser hydrogen bond capture site, and its adsorption capacity reached the highest value in the series. It is worth noting that Comparative Example 2 showed a faster adsorption rate in the early stage of adsorption, which was due to its unfilled and unobstructed pore structure that facilitated the rapid diffusion of ammonia molecules. However, due to the lack of strong hydrogen bond synergy provided by polyaniline, its adsorption capacity eventually reached saturation and was at its lowest. This comparison strongly confirms that the triple synergistic mechanism of heterometallic Lewis acid sites, sulfonic acid Brønsted acid sites, and polyaniline hydrogen bond sites is the key to achieving efficient ammonia capture.

[0098] In summary, the heterometallic-organic framework confined polyaniline composite adsorbent of the present invention can effectively adsorb low concentrations of ammonia. Therefore, the heterometallic-organic framework confined polyaniline composite adsorbent of the present invention can be used to prepare ammonia adsorption materials.

[0099] 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.

[0100] 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 technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a heterometallic-organic framework confined polyaniline composite adsorbent, characterized in that, The preparation method involves using a chromium-copper heterometallic combination to construct stable Lewis acid sites in the MIL-101 framework; then introducing sulfonic acid groups through a ligand exchange strategy to establish Brønsted acid sites; finally, confining and polymerizing aniline within the MOF channels to form abundant hydrogen bond sites, thus obtaining a heterometallic-organic framework confined polyaniline composite adsorbent.

2. The preparation method according to claim 1, wherein, The preparation method includes the following steps: To prepare the precursor solution, weigh out the chromium source and copper source and add them to the solvent, then add terephthalic acid and stir at room temperature for 30-60 minutes to obtain the precursor solution. A heterometallic MOF with Lewis acid sites was synthesized by transferring the precursor solution to a high-pressure reactor and reacting it at 200–220 °C for 5–24 h. The mixture was then naturally cooled to room temperature, and the solid product was collected by centrifugation. The solid product was washed three times each with DMF, 1–5% ammonium fluoride solution, and deionized water at 60–80 °C. The washed solid product was then placed in a vacuum drying oven and activated at 120–150 °C for 4–8 h to obtain the heterometallic MOF framework with Lewis acid sites. Brønsted acid sites were constructed by dispersing a heterometallic MOF framework in deionized water, adding monosodium 2-sulfonic acid terephthalate, and then heating to 70–90 °C and stirring under reflux for 12–36 h. After the reaction was completed, the product obtained by centrifugation was repeatedly washed with DMF and deionized water at 60–80 °C until the filtrate was neutral and colorless. Then, it was vacuum dried at 100–120 °C for 4–12 h to obtain the MIL-101-SO3H material. A physical confinement process was employed to introduce polyaniline guests. MIL-101-SO3H material was dispersed in ice-cold deionized water at 0–5°C, followed by the addition of hydrochloric acid solution and ultrasonic treatment for 10–20 min to obtain a suspension. Then, under continuous stirring and an ice bath, freshly distilled aniline monomer was slowly added dropwise while stirring continued for 1–3 h. Ammonium persulfate was dissolved in ice-cold deionized water to obtain an APS solution. The APS solution was then added dropwise to the suspension at 0–5°C to initiate a polymerization reaction. After the addition was complete, the reaction continued in an ice bath for 12–24 h. The precipitate obtained by centrifugation was washed repeatedly with deionized water and ethanol until the filtrate was colorless. Finally, the precipitate was dried in a vacuum environment at 50–80°C for 6–12 h to obtain a heterometallic-organic framework confined polyaniline composite adsorbent.

3. The preparation method according to claim 2, wherein, In the step of preparing the precursor solution, the molar ratio of chromium in the chromium source to copper in the copper source is (5-10):1, the chromium source is chromium nitrate nonahydrate, and the copper source is copper nitrate trihydrate; the molar ratio of terephthalic acid to the total molar ratio of chromium and copper is (1-1.5):

1.

4. The preparation method according to claim 2, wherein, In the step of preparing the precursor solution, the solvent is an aqueous solution containing 0-20% by volume N,N-dimethylformamide.

5. The preparation method according to claim 2, wherein, In the step of preparing the precursor solution, after adding terephthalic acid, a mineralizing agent is added, and the mixture is stirred at room temperature for 30-60 minutes to obtain the precursor solution. The mineralizing agent is a mixture of concentrated nitric acid and glacial acetic acid in a volume ratio of 1:(50-100).

6. The preparation method according to claim 2, wherein, In the step of constructing the Brønsted acid site, the mass ratio of the 2-sulfonic acid monosodium terephthalate to the heterometallic MOF framework is (2-3):

1.

7. The preparation method according to claim 2, wherein, In the step of introducing the polyaniline guest into the physical confinement, the concentration of the hydrochloric acid solution is 0.05 mol / L, and the mass-to-volume ratio of the MIL-101-SO3H material to the hydrochloric acid solution is 1000 mg: 1 mL.

8. The preparation method according to claim 2, wherein, In the step of introducing polyaniline guest material into the physical confinement, the mass-to-volume ratio of the MIL-101-SO3H material to the aniline monomer is 1000 mg: (1-5) mL, and the molar ratio of the ammonium persulfate to the aniline monomer is (1-1.2):

1.

9. A heterometallic-organic framework confined polyaniline composite adsorbent, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of the heterometallic-organic framework confined polyaniline composite adsorbent according to claim 9 in the preparation of ammonia adsorption materials.

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