Preparation method and application of salt template of two-dimensional gamma-cyclodextrin MOF nanosheet

Abstract

The invention relates to the technical field of preparation of metal organic framework materials, discloses a preparation method and application of a salt template of a two-dimensional gamma-cyclodextrin MOF nanosheet, and adopts a functionalized multistage salt template of which the surface is grafted with a gamma-cyclodextrin affinity polymer brush. The preparation method comprises the following steps: loading a precursor solution of gamma-cyclodextrin and alkali on a template for in-situ growth, then removing a multi-stage template step by step through a selective solvent, and carrying out ultrasonic stripping, purification and drying to finally obtain the two-dimensional gamma-cyclodextrin MOF nanosheet. According to the method, the two-dimensional growth of the MOF is effectively guided by utilizing the anchoring effect of the functionalized template on the precursor, so that the morphology of the nanosheet is accurately controlled. The obtained nanosheet has the advantages of high purity, complete structure and large specific surface area (300-500m < 2 > / g), and has a good application prospect in the fields of catalysis, adsorption and separation.

Description

Technical Field

[0001] This invention relates to the field of metal-organic framework material preparation technology, specifically to the preparation method and application of salt templates for two-dimensional γ-cyclodextrin MOF nanosheets. Background Technology

[0002] γ-cyclodextrin metal-organic frameworks have shown application potential in asymmetric catalysis, chiral separation, and drug delivery due to their renewable source, good biocompatibility, and inherent chiral pore structure.

[0003] The catalytic and adsorption properties of materials largely depend on their microstructure and specific surface area. Compared to traditional three-dimensional bulk crystals, MOF materials with two-dimensional nanosheet structures can expose more active sites and shorten mass transfer pathways, thus offering greater advantages in applications.

[0004] Currently, the main methods for preparing two-dimensional MOF nanosheets include top-down exfoliation and bottom-up direct synthesis. Exfoliation typically requires subjecting the already formed three-dimensional bulk crystals to strong ultrasonic treatment or chemical intercalation. This process is harsh and can easily lead to irreversible damage to the nanosheet structure, while also making it difficult to control the uniformity of the product size and thickness.

[0005] While direct synthesis aims to construct two-dimensional structures at the molecular level, effectively suppressing the vertical growth of MOF crystals remains a technical challenge in practice. The growth process often involves the stacking, aggregation, or transformation into three-dimensional crystals of nanosheets, resulting in unsatisfactory morphology of the final product and making it difficult to obtain high-quality monolayer or few-layer nanosheets.

[0006] Salt templates, as an effective method for constructing porous materials, have also been applied to the preparation of MOFs. However, conventional salt templates only provide a physically confined space, and there is a lack of specific interactions between their surface and the MOF precursor, making it impossible to effectively guide the nucleation and growth process of MOFs. This results in a high degree of randomness in the loading and crystallization process of the precursor on the template surface, making it difficult to form continuous and uniform two-dimensional nanosheet structures. Furthermore, the subsequent removal of the template can also damage the already formed fragile nanosheets.

[0007] Therefore, developing a method to precisely control the nucleation and growth process of γ-CD-MOF, thereby stably preparing two-dimensional nanosheets with complete structure and uniform morphology, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a method for preparing salt templates for two-dimensional γ-cyclodextrin MOF nanosheets and its application, which solves the problems of inaccurate morphology control of γ-cyclodextrin MOF nanosheets, structural damage caused by template removal and nanosheet exfoliation processes, and insufficient application performance due to limited exposure of active sites in the material in existing technologies.

[0009] To address the above problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preparing a salt template for two-dimensional γ-cyclodextrin MOF nanosheets, comprising the following steps: S1. Provision of Functionalized Multilevel Salt Templates: Functionalized multilevel salt templates with polymer brushes having an affinity for γ-cyclodextrin grafted onto their surfaces were prepared. This template was prepared by mixing and assembling a primary salt template with a larger particle size with a secondary salt template with a smaller particle size, then fixing a polymer anchoring initiator, and finally grafting the polymer brushes via a surface-initiated polymerization reaction.

[0010] S2. Preparation and loading of precursor solution: γ-cyclodextrin and base are dissolved in a specific molar ratio to form a precursor solution, which is then loaded onto a functionalized multilevel salt template to prepare for the growth reaction.

[0011] S3. Growth reaction: Under preset temperature (20-70℃) and time (6-48 hours) conditions, a growth reaction is carried out to synthesize γ-cyclodextrin MOF in situ on the surface of a functionalized multi-level salt template, forming a γ-cyclodextrin MOF@multi-level salt template complex.

[0012] S4. Removal of primary template: The primary salt template is removed by treating the complex in the selective solvent step.

[0013] S5. Exfoliation of two-dimensional nanosheets: The solid after removing the primary template is immersed in a second solvent, and the γ-cyclodextrin MOF nanosheets are exfoliated from the secondary salt template by physical means (such as ultrasonic treatment).

[0014] S6. Separation and purification of nanosheets: Using techniques such as centrifugation and washing, the exfoliated γ-cyclodextrin MOF nanosheets were separated and purified from the solution to obtain high-purity two-dimensional γ-cyclodextrin MOF nanosheets.

[0015] S7. Drying of nanosheets: The purified nanosheets are dried to obtain the target product.

[0016] By employing the above-mentioned technical solution, the design and preparation of functionalized hierarchical salt templates optimize the salt template, thereby improving the growth efficiency of γ-cyclodextrin MOFs. Simultaneously, the use of specific precursor solutions and reaction conditions ensures that the formed nanosheets not only have a uniform structure but also possess high specific surface area and catalytic performance. Therefore, the obtained two-dimensional γ-cyclodextrin MOF nanosheets have significant application potential in catalysis and adsorption.

[0017] Preferably, the molar ratio of γ-cyclodextrin to base in the precursor solution is set to 1:(6-12), which can significantly improve reaction efficiency and product quality.

[0018] By adopting the above technical solution, the present invention has achieved efficient preparation of two-dimensional γ-cyclodextrin MOF nanosheets, laying a good foundation for their application in catalysis, adsorption and other fields.

[0019] Secondly, this invention provides the application of two-dimensional γ-cyclodextrin MOF nanosheets, employing the following technical solution: A method for preparing a material for catalysis, adsorption, or separation includes the following steps: Preparation of two-dimensional γ-cyclodextrin MOF nanosheets: Two-dimensional γ-cyclodextrin MOF nanosheets were prepared using the salt template method described above.

[0020] Catalytic Application: Exploring the performance of two-dimensional γ-cyclodextrin MOF nanosheets in catalytic ester hydrolysis reactions. Experimental results show that the prepared nanosheets exhibit excellent catalytic activity, accelerating the hydrolysis rate of esters and improving reaction efficiency.

[0021] Adsorption Application: The performance of two-dimensional γ-cyclodextrin MOF nanosheets as adsorbents was evaluated, and their adsorption capacity for target molecules was tested. Tests showed that the nanosheets, due to their high specific surface area (300-500 m²), exhibited good adsorption properties. 2 With its specific pore structure ( / g), it can effectively adsorb various organic pollutants.

[0022] Applications of membrane and separation materials: Based on practical needs, two-dimensional γ-cyclodextrin MOF nanosheets are used as membrane materials or separating agents to prepare membranes, and their performance in gas separation, liquid filtration, and other fields is further studied. These applications expand the practical use of the material and make full use of its excellent physicochemical properties.

[0023] By employing the above-mentioned technical solutions, two-dimensional γ-cyclodextrin MOF nanosheets exhibited high selectivity and catalytic efficiency in various catalytic and adsorption reactions. Particularly in the catalytic hydrolysis of esters, they achieved good reaction conversion and selectivity, providing a new concept for environmental protection and resource recycling. Furthermore, their long-term stability and reproducibility in practical applications were fully verified, improving the feasibility of industrial applications.

[0024] Preferably, the BET specific surface area of ​​the two-dimensional γ-cyclodextrin MOF nanosheets is 300-500 m². 2 / g, this characteristic enables it to exhibit excellent performance in catalysis and adsorption processes.

[0025] By adopting the above technical solution, this invention not only broadens the application scope of two-dimensional γ-cyclodextrin MOF nanosheets, but also provides a new material basis and development prospects for research and technological applications in related fields.

[0026] This invention provides a method for preparing salt templates for two-dimensional γ-cyclodextrin MOF nanosheets and its application, which has the following beneficial effects: 1. This invention achieves precise control over the morphology of two-dimensional γ-cyclodextrin MOF nanosheets by designing functionalized multi-level salt templates. The γ-cyclodextrin affinity polymer brushes on the template surface effectively capture and anchor precursor molecules, guiding their restricted two-dimensional growth on the template surface and suppressing uncontrolled three-dimensional nucleation and crystallization in solution. This surface-initiated polymerization-based functionalization strategy ensures that the final product is a two-dimensional nanosheet structure with uniform thickness and a large lateral dimension.

[0027] 2. The multi-stage salt template and stepwise removal strategy employed in this invention ensure the high purity and structural integrity of the final product. By using tetrahydrofuran, which has a high selective solubility for the primary template, the internal template can be effectively removed without damaging the MOF nanosheet structure grown on the secondary template. Subsequent gentle ultrasonic exfoliation in methanol separates the nanosheets from the secondary template surface while avoiding breakage or stacking of the nanosheets due to harsh processing, thus obtaining a product with intact structure and good dispersibility.

[0028] 3. The two-dimensional γ-cyclodextrin MOF nanosheets prepared by this invention exhibit excellent application performance, thanks to their unique two-dimensional structure and high specific surface area. This two-dimensional morphology allows for higher exposure and accessibility of the γ-cyclodextrin cavities and metal active sites within the material. This high specific surface area provides a large number of active sites for catalytic reactions and molecular adsorption, thus demonstrating higher reaction efficiency and performance in applications such as catalytic ester hydrolysis. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to embodiments, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Preparation Examples 1-3: Preparation Example 1: Preparation of Functionalized Multilevel Salt Templates This preparation example provides a method for preparing a multi-level salt template with a γ-cyclodextrin affinity polymer brush grafted on its surface with medium chain length / density, including the following steps: Template Assembly: 50.0g of sodium chloride crystals were recrystallized in a saturated aqueous solution. Cubic crystals with a particle size of 100-200μm were collected by sieving and used as secondary templates (T2). Another 10.0g of lithium chloride crystals with a particle size of 1-2mm, obtained through grinding and sieving, were used as primary templates (T1). T1 and T2 crystals were physically mixed at a mass ratio of 1:5. A small amount of ethanol (enough to wet the crystal surface but not to completely dissolve it) was added, and the mixture was slowly evaporated to dryness on a rotary evaporator, allowing T2 crystals to uniformly adhere to the surface of T1 crystals, forming a multi-level composite template.

[0031] Anchoring initiator fixation: 1.0 g of polystyrene-maleic anhydride was dissolved in 100 mL of acetone. The multi-level composite template prepared by template assembly was added, and the mixture was magnetically stirred at 30 °C for 30 minutes. Subsequently, the acetone was slowly evaporated to dryness on a rotary evaporator at 40 °C and -0.1 MPa, anchoring the PSMA to the template surface. The template was ultrasonically washed three times with 100 mL of n-hexane to remove physically adsorbed PSMA. Finally, it was vacuum dried at 60 °C for 4 hours.

[0032] Surface-initiated polymerization: In a nitrogen-filled anhydrous and oxygen-free glove box, the template with the anchored initiator was placed in a Schlenk reaction flask. 9.24 g (45.0 mmol) of N-adamantylacrylamide (AdAAm, molar mass 205.29 g / mol), 0.065 g (0.45 mmol) of cuprous bromide (Cu(I)Br, molar mass 143.45 g / mol) and 0.104 g (0.45 mmol) of N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA, molar mass 231.45 g / mol) were added sequentially. After purging with nitrogen three times, 100 mL of deoxygenated anhydrous toluene was injected using a syringe. The reaction system was sealed and the reaction was magnetically stirred at 50 °C for 12 hours.

[0033] Purification and Drying: After the reaction, the product was diluted with a large amount of toluene and filtered. The collected template was subjected to Soxhlet extraction with toluene, tetrahydrofuran, and methanol, or repeated ultrasonic washing, until the washing solution was clear and transparent, to completely remove the catalyst, ligands, and unreacted monomers. Finally, the obtained functionalized hierarchical salt template was vacuum dried at 60 °C for 12 hours, denoted as Template-M.

[0034] Preparation Example 2: Preparation of Functionalized Multilevel Salt Templates This preparation example provides a method for preparing a multi-level salt template with a γ-cyclodextrin affinity polymer brush grafted on its surface with shorter chain length / lower density, including the following steps: The template assembly and anchoring initiator fixation steps are exactly the same as those in Preparation Example 1.

[0035] Surface-initiated polymerization: The polymerization steps were basically the same as those for the surface-initiated polymerization in Preparation Example 1, except that the reaction conditions were changed: the template with the anchored initiator, 9.24 g (45.0 mmol) AdAAm, 0.065 g (0.45 mmol) Cu(I)Br, and 0.104 g (0.45 mmol) PMDETA were mixed with 100 mL of anhydrous toluene. The reaction system was sealed and magnetically stirred at 25 °C for 1 hour.

[0036] The purification and drying steps were exactly the same as in Preparation Example 1. The final functionalized multilevel salt template was denoted as Template-L.

[0037] Preparation Example 3: Preparation of Functionalized Multilevel Salt Templates This preparation example provides a method for preparing a multi-level salt template with a γ-cyclodextrin affinity polymer brush grafted on its surface with a longer chain length / higher density, including the following steps: The template assembly and anchoring initiator fixation steps are exactly the same as those in Preparation Example 1.

[0038] Surface-initiated polymerization: The polymerization steps were basically the same as those for the surface-initiated polymerization in Preparation Example 1, except that the reaction conditions were changed: the template with the anchored initiator, 9.24 g (45.0 mmol) AdAAm, 0.065 g (0.45 mmol) Cu(I)Br, and 0.104 g (0.45 mmol) PMDETA were mixed with 100 mL of anhydrous toluene. The reaction system was sealed and magnetically stirred at 70 °C for 24 hours.

[0039] The purification and drying steps were exactly the same as in Preparation Example 1. The final functionalized multilevel salt template was denoted as Template-H.

[0040] Examples 1-3: Example 1: This embodiment provides a method for preparing salt templates for two-dimensional γ-cyclodextrin MOF nanosheets and their application, including the following steps: S1. Preparation of precursor solution: Weigh 0.285 g (0.22 mmol) γ-CD and 0.099 g (1.76 mmol) KOH (molar ratio 1:8) and dissolve them together in 5 mL of deionized water. Sonicate the mixture at room temperature for 15 minutes to form a clear and homogeneous precursor solution.

[0041] S2, Template Loading: 10g of the functionalized multi-level salt template (Template-M) prepared in Preparation Example 1 was added to the precursor solution prepared in step S1. The mixture was magnetically stirred at 400 rpm for 30 minutes to ensure that the precursor solution was fully and uniformly loaded onto the template surface and pores. Excess precursor solution was then removed by filtration.

[0042] S3, Field-Assisted Growth: The template loaded with the precursor solution was sealed in a reaction vessel and allowed to stand at 40°C for 24 hours. During this growth process, an ultrasonic field (frequency 40kHz, power density 0.5W / cm²) was applied once per hour. 2 Each application lasts 5 minutes.

[0043] S4, Primary Template (T1) Removal: After the reaction, the complex was transferred to 100 mL of tetrahydrofuran (THF) and treated with magnetic stirring for 2 hours to dissolve and remove the LiCl template. After treatment, the remaining solid (γ-CD-MOF@NaCl complex) was collected by centrifugation (3000 rpm, 5 minutes).

[0044] S5. Two-dimensional nanosheet exfoliation: The solid obtained in step S4 was dispersed in 100 mL of methanol and ultrasonically treated at 400 W for 30 minutes to promote the exfoliation of γ-CD-MOF nanosheets from the NaCl template surface.

[0045] S6. Separation and Purification: After ultrasonic treatment, the suspension was allowed to stand for 10 minutes to allow the denser NaCl template to settle. The supernatant was carefully separated by decantation, and then centrifuged (5000 rpm, 10 minutes) to collect the γ-CD-MOF nanosheets. The nanosheets were then centrifuged and redispersed three times with fresh methanol.

[0046] S7. Drying: The purified nanosheets were vacuum dried at 50°C for 8 hours to obtain the final product, denoted as S1.

[0047] Example 2: This embodiment provides a method for preparing salt templates for two-dimensional γ-cyclodextrin MOF nanosheets and their application, including the following steps: S1. Preparation of precursor solution: Weigh 0.285 g (0.22 mmol) γ-CD and 0.074 g (1.32 mmol) KOH (molar ratio 1:6), and dissolve them together in a mixed solvent of 9 mL deionized water and 1 mL ethanol. Sonicate the mixture at room temperature for 5 minutes to form a clear and homogeneous precursor solution.

[0048] S2, Template Loading: 10g of the functionalized multi-level salt template (Template-L) prepared in Preparation Example 2 was added to the precursor solution prepared in step S1. The mixture was magnetically stirred at 100 rpm for 10 minutes to ensure that the precursor solution was fully and uniformly loaded onto the template surface and pores. Excess precursor solution was then removed by filtration.

[0049] S3, Field-assisted growth: The template loaded with the precursor solution was sealed in a reaction vessel and allowed to stand at 20°C for 6 hours. No external physical field was applied during this growth process.

[0050] S4, Primary Template (T1) Removal: After the reaction was complete, the complex was transferred to 100 mL of tetrahydrofuran (THF) and treated with magnetic stirring for 1 hour to dissolve and remove the LiCl template. After treatment, the remaining solid was collected by centrifugation (3000 rpm, 5 minutes).

[0051] S5, Two-dimensional nanosheet exfoliation: The solid obtained in step S4 is dispersed in 100 mL of methanol and ultrasonically treated for 10 minutes at an ultrasonic power of 100 W.

[0052] S6. Separation and Purification: After sonication, the suspension was allowed to stand for 10 minutes to allow the denser NaCl template to settle. The supernatant was carefully separated by decantation, and then centrifuged (3000 rpm, 10 minutes) to collect the γ-CD-MOF nanosheets. The nanosheets were then centrifuged twice with fresh methanol for redispersion and washing.

[0053] S7. Drying: The purified nanosheets were vacuum dried at 25°C for 4 hours to obtain the final product, denoted as S2.

[0054] Example 3: This embodiment provides a method for preparing salt templates for two-dimensional γ-cyclodextrin MOF nanosheets and their application, including the following steps: S1. Preparation of precursor solution: Weigh 0.285 g (0.22 mmol) γ-CD and 0.148 g (2.64 mmol) KOH (molar ratio 1:12), and dissolve them together in a mixed solvent of 2.5 mL deionized water and 2.5 mL methanol. Sonicate the mixture at room temperature for 30 minutes to form a clear and homogeneous precursor solution.

[0055] S2, Template Loading: 10 g of the functionalized multi-level salt template (Template-H) prepared in Preparation Example 3 was added to the precursor solution prepared in step S1. The mixture was magnetically stirred at 800 rpm for 60 minutes to ensure that the precursor solution was fully and uniformly loaded onto the template surface and pores. Excess precursor solution was then removed by filtration.

[0056] S3, Field-assisted growth: The template loaded with the precursor solution was sealed in a reaction vessel and allowed to stand at 60°C for 48 hours. During this growth process, a DC electric field of 5V / cm was applied across the reaction system.

[0057] S4, Primary Template (T1) Removal: After the reaction was complete, the complex was transferred to 100 mL of tetrahydrofuran (THF) and treated with magnetic stirring for 4 hours to dissolve and remove the LiCl template. After treatment, the remaining solid was collected by centrifugation (3000 rpm, 5 minutes).

[0058] S5, Two-dimensional nanosheet exfoliation: The solid obtained in step S4 is dispersed in 100 mL of methanol and ultrasonically treated for 60 minutes at an ultrasonic power of 500 W.

[0059] S6. Separation and Purification: After sonication, the suspension was allowed to stand for 10 minutes to allow the denser NaCl template to settle. The supernatant was carefully separated by decantation, and then centrifuged (8000 rpm, 10 minutes) to collect the γ-CD-MOF nanosheets. The nanosheets were then centrifuged and redispersed four times with fresh methanol.

[0060] S7. Drying: The purified nanosheets were vacuum dried at 60°C for 12 hours to obtain the final product, denoted as S3.

[0061] Comparative Examples 1-5: Comparative Example 1: Preparation of γ-CD-MOF using the conventional gas-phase diffusion method This comparative example uses a gas-phase diffusion method known in the art to prepare γ-CD-MOF. The same amount of γ-CD and KOH as in step S1 of Example 1 were dissolved in 20 mL of deionized water to obtain a clear solution. This solution was placed in a 50 mL open beaker, and then placed in a 250 mL sealed desiccator containing 30 mL of ethanol at the bottom. The desiccator was sealed at 25°C and allowed to stand for 7 days. After blocky crystals precipitated, the crystals were collected and dried to obtain the product, denoted as D1.

[0062] Comparative Example 2: Template-free solution crystallization Compared to Example 1, the difference lies in that the precursor solution prepared in step S1 was placed directly at 40°C for 24 hours without the addition of any salt template to allow it to crystallize naturally. After the reaction was completed, the precipitate was collected by filtration, washed with methanol, and dried to obtain the product, denoted as D2.

[0063] Comparative Example 3: Using a non-functionalized single salt template Compared to Example 1, the difference lies in that the template used in step S2 is pure NaCl crystals (particle size 100-200 μm) that have not undergone any functionalization steps in Preparation Example 1. Since the LiCl(T1) template is absent, the THF washing process in step S4 is omitted. The remaining steps are the same as in Example 1, yielding a product denoted as D3.

[0064] Comparative Example 4: Growth without external physical field assistance The only difference from Example 1 is that no intermittent ultrasonic field was applied during the static growth process in step S3; that is, the reaction was carried out at 40°C for 24 hours. All other steps were exactly the same as in Example 1, yielding a product denoted as D4.

[0065] Comparative Example 5: A functionalized single salt template (without multi-level structure) was used. Compared to Example 1, the difference lies in that the template used in step S2 is a single NaCl crystal (T2) that has only undergone functionalization treatment according to the method of Preparation Example 1, rather than a multi-level template composed of LiCl / NaCl. Accordingly, the step of removing the primary template (T1) with THF in step S4 is omitted. The remaining steps are exactly the same as in Example 1, yielding a product denoted as D5.

[0066] Test Examples 1-5: Test Example 1: Success Verification of Template Surface Functionalization This test example aims to verify the successful grafting of the anchoring initiator PSMA and the functional polymer PAdAAm by analyzing the changes in chemical composition on the surface of the salt template. The surface chemical properties of the untreated salt template, the PSMA-anchored salt template, and the functionalized salt template obtained in Preparation Example 1 were characterized by Fourier transform infrared spectroscopy (FTIR) and elemental analysis (EA).

[0067] Experimental steps: Sample preparation: Control sample: A certain amount of pure NaCl crystals that have undergone recrystallization were taken as unfunctionalized salt templates.

[0068] Intermediate sample: The PSMA-anchored salt template obtained after the anchoring initiator fixation in Preparation Example 1 was completed.

[0069] Functionalized sample: Take the functionalized multi-level salt template (Template-M) obtained after purification and drying in Preparation Example 1.

[0070] Grind the three samples into a fine powder and set aside.

[0071] Fourier transform infrared spectroscopy (FTIR) analysis: Each sample powder was mixed with spectral grade KBr at a mass ratio of approximately 1:100, thoroughly ground, and then pressed into a transparent sheet.

[0072] Measurements were performed using a Nicoleti S50 FTIR spectrometer. The scanning range was 4000 cm⁻¹. -1 Up to 400cm -1 4cm resolution -1 A total of 32 scans were performed. The infrared absorption spectra of each sample were collected and recorded.

[0073] Elemental Analysis (EA): Accurately weigh approximately 5-10 mg of each sample powder.

[0074] The mass percentages of carbon (C), hydrogen (H), and nitrogen (N) in each sample were determined using an Elementar Vario ELcube elemental analyzer.

[0075] Experimental data: Table 1. Analytical results of chemical composition of functionalized salt template surface In summary, this test case systematically verified the successful implementation of salt template surface functionalization through Fourier transform infrared spectroscopy and elemental analysis. The untreated NaCl template mainly exhibited characteristic peaks of CO2 and adsorbed water from the environment in the FTIR spectrum. Elemental analysis results showed that the carbon, hydrogen, and nitrogen contents were close to zero, which is consistent with its bulk properties as an inorganic salt.

[0076] When PSMA is anchored on the salt template surface, the FTIR spectrum is at 1780 cm⁻¹. -1 and 1710cm -1 A distinct strong absorption peak appeared nearby, corresponding to the carbonyl stretching vibrations of the anhydride in PSMA and the carboxylic acid after hydrolysis, respectively, and also at 2920 cm⁻¹. -1 The presence of a CH stretching vibration peak indicates that the PSMA has been successfully anchored to the template surface. Elemental analysis further supports this conclusion, showing a significant increase in the mass percentages of carbon and hydrogen, while the nitrogen content remains at extremely low levels, consistent with the molecular composition of PSMA.

[0077] After the PAdAAm polymer was brush-grafted onto the PSMA-anchored template surface, the FTIR spectrum underwent further changes. (1780 cm⁻¹) -1 and 1710cm -1 The absorption peak intensity at 1650 cm⁻¹ is relatively weakened or shifted, while at 1650 cm⁻¹... -1 (Amide I band, C=O stretching vibration) and 1540cm -1A new strong absorption peak appeared at the amide II band (NH bending vibration), clearly indicating the polymerization of AdAAm monomers to form a polyamide structure. Furthermore, the intensity of the CH stretching vibration peak was further enhanced. Elemental analysis data provided quantitative evidence: the contents of carbon and hydrogen increased significantly again, and more importantly, the mass percentage of nitrogen increased dramatically from near zero to 1.37 wt%. Since PAdAAm is the only component that introduced nitrogen into the system, the significant increase in nitrogen content directly proves the successful grafting of the PAdAAm polymer brush.

[0078] In summary, the combined evaluation of FTIR and EA analysis results indicates that the surface functionalization process of the multi-level salt template—namely, the anchoring of PSMA and the grafting of PAdAAm polymer brushes—has been successfully achieved. The adamantyl structure contained in the PAdAAm polymer brushes can form host-guest inclusion complexes with γ-cyclodextrin, thereby providing highly selective nucleation sites and guidance for γ-CD-MOF in the precursor solution. This precise surface functionalization is the core foundation of the structure-guided and modified synergistic strategy of the salt template in this invention. It enhances the directional growth mechanism of the γ-CD-MOF two-dimensional structure through chemical affinity rather than simple physical confinement, laying a solid chemical foundation for the subsequent precise control and optimization of nanosheet morphology.

[0079] Test Example 2: Feasibility Verification of Selective Removal of Multi-Level Templates This test example aims to verify the feasibility of the multi-stage selective removal of salt templates in the present invention, particularly by utilizing the differences in solubility of different salt templates in different solvents to achieve graded and selective template removal while maintaining the integrity of the γ-CD-MOF nanostructure. Inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis was used to quantitatively evaluate the template removal efficiency and product purity.

[0080] Experimental steps: Sample preparation: Accurately weigh 1.000g of the γ-CD-MOF@salt template complex after the growth reaction in step S3 of Example 1. The complex contains a LiCl / NaCl hierarchical template on which γ-CD-MOF has been grown.

[0081] Remove Level 1 template (T1): Transfer the above complex to a 250 mL beaker and add 100 mL of tetrahydrofuran (THF).

[0082] Stir at 200 rpm for 3 hours at room temperature using a magnetic stirrer.

[0083] After stirring, the filtrate (containing dissolved LiCl) was separated from the solid by vacuum filtration (using a filter membrane with a pore size of 0.22 μm).

[0084] Collect all the filtrate, take 5 mL of the sample, dilute it appropriately, and determine the Li content using ICP-OES. + Ion concentration.

[0085] The filter cake (mainly γ-CD-MOF@NaCl complex) was washed once with a small amount of THF, then vacuum dried at 50°C for 2 hours and weighed.

[0086] Secondary template (T2) peeling and separation: The dried filter cake obtained by removing the primary template (T1) was dispersed in 100 mL of methanol.

[0087] The γ-CD-MOF nanosheets were detached from the NaCl template surface by ultrasonic treatment at 400W power for 30 minutes using an ultrasonic cleaner.

[0088] After ultrasonic treatment, the suspension was allowed to stand for 10 minutes to allow the NaCl template, which has a faster sedimentation rate, to separate from the suspended γ-CD-MOF nanosheets.

[0089] The supernatant (containing γ-CD-MOF nanosheets) was carefully separated by decantation, and the supernatant was centrifuged (5000 rpm, 10 min) to collect the γ-CD-MOF nanosheets.

[0090] The separated γ-CD-MOF nanosheets were washed twice with methanol and then dried under vacuum at 50°C for 8 hours to obtain the final product.

[0091] Take 50 mg of the final product, perform acid digestion (such as nitric acid), and then determine the Na content by ICP-OES. + Ion residual concentration.

[0092] Experimental data: Table 2. Evaluation of the selective removal effect of multi-stage salt template Note: In the table, "-" indicates that for the experimental phase described in a specific row of the table, the test items represented by the specific column are irrelevant, meaningless, or cannot be measured.

[0093] Summary: This test case quantitatively verified the feasibility of the multi-stage salt template selective removal scheme in this invention through ICP-OES analysis. Experimental results show that after treating the γ-CD-MOF@LiCl / NaCl complex with THF, the Li in the filtrate... + The ion concentration is high, and the calculated Li +The removal efficiency reached 98.6%. This demonstrates that LiCl(T1), as a primary template, can be effectively and selectively dissolved and removed by THF. This process utilizes the difference between the high solubility of LiCl in THF and the extremely low solubility of NaCl in THF to achieve precise separation of the first-layer template. The reduction in filter cake mass also indirectly confirms the removal of LiCl, and the structure of the remaining solid (γ-CD-MOF@NaCl) is preserved.

[0094] After the second stage of exfoliation and purification, the final γ-CD-MOF nanosheet product was subjected to Na... + Residual analysis. Data shows that Na in the final product... + The residual amount was extremely low, only 0.004 wt%. This confirms that the strategy of ultrasonic exfoliation with methanol combined with decantation and multi-step washing can effectively and efficiently separate γ-CD-MOF nanosheets from the NaCl template (T2) and significantly reduce the residual NaCl template.

[0095] Multi-level template-assisted confined growth and exfoliation is a key innovation of this invention. The successful implementation of this strategy relies on two core mechanisms: first, the selective solubility of the template material, i.e., LiCl dissolves in THF while NaCl remains insoluble; second, the effectiveness of physical exfoliation and separation methods, i.e., ultrasonic-assisted exfoliation of nanosheets from the T2 surface. The test results provide direct evidence that the designed two-step hierarchical removal strategy is effective. This hierarchical removal method minimizes damage to the secondary template or the already formed MOF structure during the removal of the primary template, thus ensuring the preparation of high-purity, high-quality two-dimensional γ-CD-MOF nanosheets. This verification is a crucial step in supporting the feasibility of the overall technical approach of this invention.

[0096] Test Example 3: Specific Surface Area Analysis This test case aims to evaluate the BET specific surface area of ​​γ-CD-MOF samples prepared by different methods through nitrogen adsorption-desorption isotherm analysis. Specific surface area is a key parameter for measuring the porosity of materials and the number of exposed active sites, and is crucial for applications such as catalysis and adsorption.

[0097] Experimental steps: Sample pretreatment: Accurately weigh approximately 50-100 mg of each of the samples to be tested (including Examples S1-S3 and Comparative Examples D1-D5).

[0098] The sample was placed in the sample tube of the surface area analyzer and subjected to high vacuum (10 °C) at 150 °C. -5 Degassing was performed under Torr conditions for 6-12 hours to completely remove adsorbed water and impurities from the sample pores.

[0099] Nitrogen adsorption-desorption test: Cool the degassed sample tube to liquid nitrogen temperature (77K).

[0100] Nitrogen adsorption-desorption isotherms were measured using a Micromeritics ASAP2020 fully automated specific surface area and pore size analyzer.

[0101] Adsorption data points were collected within a relative pressure (P / P0) range of 0.05-0.30 for the calculation of BET specific surface area.

[0102] Data processing: Based on the Brunauer-Emmett-Teller (BET) theoretical model, the obtained nitrogen adsorption data were processed to calculate the BET specific surface area of ​​each sample.

[0103] Experimental data: Table 3. BET specific surface area of ​​γ-CD-MOF samples obtained by different preparation methods In summary, this test case demonstrates the superiority of the proposed preparation method by analyzing the BET specific surface area of ​​γ-CD-MOF samples prepared by different methods. The γ-CD-MOF nanosheets prepared in Examples S1, S2, and S3 exhibit significantly higher BET specific surface areas than those in Comparative Examples D1-D5.

[0104] Specifically, the specific surface area of ​​embodiments S1, S2, and S3 ranges from 318.9 m². 2 / g to 455.1m 2 / g, while the specific surface area of ​​comparative examples D1, D2, D3, D4, and D5 was 36.7m². 2 / g up to 340.2m 2 Between / g. Among them, the materials obtained by the traditional gas-phase diffusion method (D1) and the template-free solution crystallization method (D2) have significantly lower specific surface areas. This is attributed to the lack of morphology control in these methods, which tend to form large, dense or highly aggregated bulk crystals, thus limiting the exposed surface area.

[0105] The functionalized multi-level salt template strategy employed in this invention is a key factor in achieving a high specific surface area. The specific surface area of ​​Comparative Example D3 (unfunctionalized single template) is significantly lower than that of Example S1, indicating that template surface functionalization (i.e., grafting of PAdAAm polymer brushes) provides precise guidance for the nucleation of γ-CD-MOFs. The host-guest interaction between PAdAAm and γ-CD allows γ-CD-MOFs to selectively and directionally grow into two-dimensional nanosheet structures on their surface. This controlled two-dimensional growth suppresses the disordered growth and aggregation of three-dimensional crystals, thereby effectively increasing the externally exposed surface area.

[0106] Further comparison of Comparative Example D5 (functionalized single template) and Example S1 (functionalized multi-level template) reveals that the application of the multi-level template improves the specific surface area compared to the single template. This indicates that the multi-level template system composed of LiCl and NaCl provides a more complex confined environment and richer nucleation interfaces in space, or helps maintain the integrity and dispersion of nanosheets during subsequent exfoliation, thereby optimizing the overall exposed surface area of ​​the material.

[0107] Furthermore, the introduction of external physical fields (such as electric or ultrasonic fields) also contributes to the optimization of the material's specific surface area. The specific surface area of ​​the comparative example D4 (functionalized multi-level template, without field assistance) is 340.2 m². 2 / g, lower than Example S1 (412.5m) 2 / g) and S3 (455.1m) 2 The specific surface area is significantly lower than that of S3 (electric field assisted). This indicates that external physical fields can modulate crystallization kinetics, which can help form thinner, more uniform, or smaller two-dimensional nanosheets, thereby increasing the specific surface area.

[0108] In summary, the synergistic strategy of structure guidance and external physical field-assisted growth of the functionalized multi-level salt template of this invention can effectively control the morphology of γ-CD-MOF and promote its formation of two-dimensional nanosheet structures with high exposed surface area, providing a solid material foundation for subsequent applications in catalysis, adsorption, sensing and other fields.

[0109] Test Example 4: Colloidal Dispersion Stability Test This test case aims to evaluate the colloidal dispersion stability of γ-CD-MOF samples prepared by different methods. For two-dimensional nanomaterials, good dispersion stability is a crucial prerequisite for further processing, assembly, or application in biomedicine, catalysis, and other fields in the solution phase. By monitoring the change in absorbance of the suspension over time, the anti-sedimentation ability of the material in the solvent is quantified.

[0110] Experimental steps: Sample suspension preparation: Accurately weigh 10 mg of each of the samples to be tested (including Examples S1-S3 and Comparative Examples D1-D5).

[0111] Each sample was dispersed in 10 mL of anhydrous ethanol to prepare a suspension with a concentration of 1.0 mg / mL.

[0112] Each suspension was sonicated using an ultrasonic probe (e.g., 100W power, 20kHz frequency, for 10 minutes) to ensure initial dispersion uniformity.

[0113] Absorbance monitoring: Immediately after ultrasonic treatment, 1 mL of the suspension was transferred to a cuvette with a 1 cm optical path.

[0114] Using a UV-Vis spectrophotometer (e.g., Shimadzu UV-2600), absorbance values ​​were recorded every minute at a wavelength of 600 nm for 30 minutes. The initial absorbance was recorded as A0, and the absorbance after 30 minutes was recorded as A... 30 .

[0115] Data processing: According to the formula: Dispersion stability = (A) 30 Calculate the absorbance retention rate of each sample after 30 minutes by multiplying ( / A0) by 100%. A higher retention rate indicates better dispersion stability.

[0116] Experimental data: Table 4. Colloidal dispersion stability assessment of γ-CD-MOF samples obtained by different preparation methods Summary: This test example quantitatively evaluated the colloidal dispersion stability of different γ-CD-MOF samples by monitoring their absorbance retention in ethanol suspensions. Experimental results show that the γ-CD-MOF nanosheets (S1-S3) prepared by the method of this invention exhibit significantly better dispersion stability than the comparative samples (D1-D5). The absorbance retention rates of Examples S1, S2, and S3 ranged from 72.3% to 91.5%, while the retention rates of Comparative Examples D1-D5 ranged from 8.9% to 69.1%.

[0117] The samples prepared by comparative examples D1 (traditional gas-phase diffusion method) and D2 (template-free solution crystallization method) exhibited extremely poor dispersion stability, with absorbance retention rates of only 15.2% and 8.9%, respectively. This is attributed to the fact that the products of these traditional methods are macroscopic bulk crystals or disordered aggregates, lacking clear two-dimensional structural features, and are prone to rapid sedimentation in solution.

[0118] The functionalized multi-level salt template strategy employed in this invention plays a crucial role in enhancing dispersion stability. Comparing Comparative Example D3 (unfunctionalized single template, retention rate 35.7%) with Example S1 (functionalized multi-level template, retention rate 88.6%), the introduction of the functionalized template significantly improves dispersion stability. The PAdAAm polymer brush guides the orderly growth of γ-CD-MOF on the template surface through specific interactions with γ-CD. This process facilitates the formation of two-dimensional nanosheets with regular morphology and uniform thickness. Furthermore, the polymer brush itself imparts certain surface solubility or steric hindrance effects to the nanosheets after exfoliation, thereby inhibiting non-specific aggregation between nanosheets and improving their stability in solution.

[0119] Comparing Comparative Example D5 (functionalized single template, retention rate 55.4%) with Example S1 (functionalized multi-level template, retention rate 88.6%), the application of multi-level templates further enhanced dispersion stability. Multi-level templates can provide a finer confined growth space, which helps to obtain nanosheets with more uniform lateral dimensions and lower defect density, or reduce mechanical damage to nanosheets during exfoliation, thereby reducing their tendency to aggregate in solution.

[0120] Furthermore, the strategy of external physical field-assisted growth also has a positive impact on dispersion stability. The stability of Comparative Example D4 (functionalized multi-level template, no field assistance, retention rate 69.1%) was lower than that of Examples S1 (ultrasonic field assistance, retention rate 88.6%) and S3 (electric field assistance, retention rate 91.5%). The introduction of an external field modulates the nucleation rate and crystal growth orientation during the crystallization process, which is beneficial for forming a smoother and more uniform nanosheet surface and reducing edge defects. These factors all contribute to improving the colloidal dispersion performance of nanosheets in solution.

[0121] In summary, the synergistic strategy of structure guidance using functionalized multi-level salt templates and external physical field-assisted growth in this invention enables precise control over the morphology and surface properties of γ-CD-MOF two-dimensional nanosheets. This precise structural control effectively suppresses the disordered growth and aggregation of nanosheets, thereby endowing them with excellent colloidal dispersion stability, which is crucial for their stability and functionality in various liquid-phase applications.

[0122] Test Example 5: Active Site Exposure Assessment (Catalytic Performance Test) This test case aims to evaluate the catalytic activity of γ-CD-MOF samples prepared by different methods through a model catalytic reaction—the hydrolysis of p-nitrophenol acetate. The hydrophobic cavity of γ-cyclodextrin can serve as a catalytically active site. Therefore, the reaction rate is directly related to the exposure and accessibility of γ-cyclodextrin active sites in the material.

[0123] Experimental steps: Preparation of reaction solution: Prepare a phosphate buffer solution (PBS, 0.1M, pH=7.4).

[0124] Preparation of nitrophenol acetate substrate stock solution: Dissolve nitrophenol acetate in acetonitrile to a concentration of 10 mM.

[0125] Catalytic reaction: In a cuvette kept at a constant temperature (30°C), add 2.8 mL of PBS buffer solution and 100 μL of γ-CD-MOF sample ethanol suspension (1.0 mg / mL) to bring the final catalyst concentration to 0.033 mg / mL. Incubate the mixture at a constant temperature for 5 minutes.

[0126] Quickly add 100 μL of PNPA substrate stock solution to the cuvette to start the reaction. The initial concentration of nitrophenol acetate is 0.33 mM.

[0127] Immediately use a UV-Vis spectrophotometer to continuously monitor the amount of p-nitrophenol produced at a wavelength of 400 nm (i.e., the increase in absorbance), recording data every 30 seconds for 10 minutes.

[0128] Data processing: Under conditions of substrate excess, this reaction can be considered a pseudo-first-order reaction.

[0129] By plotting ln(A∞-At) against time t, where A∞ is the absorbance at the reaction endpoint and At is the absorbance at time t, the slope of the linear fit of the plot is the apparent rate constant k(min). -1 ).

[0130] Experimental data: Table 5. Apparent rate constants for PNPA hydrolysis catalyzed by different γ-CD-MOF samples Summary: This test example evaluated the catalytic activity of different γ-CD-MOF samples by monitoring the hydrolysis rate of p-nitrophenol acetate. This activity directly reflects the exposure degree of γ-cyclodextrin active sites on their surface. The data show that the catalytic activity of the samples prepared by the method of this invention (S1-S3) is significantly higher than that of all comparative samples (D1-D5).

[0131] The apparent rate constant k values ​​for Examples S1, S2, and S3 range from 0.091 to 0.153 min. -1 In contrast, the k-values ​​for comparative examples D1-D5 ranged only from 0.0047 to 0.073 min. -1Among them, comparative examples D1 (conventional gas-phase diffusion method) and D2 (template-free solution crystallization method) exhibited extremely low catalytic activity, with their k values ​​approaching the background reaction rate. This is highly correlated with the specific surface area data of test example 3. The extremely low surface area resulted in most of the γ-cyclodextrin active sites being embedded inside the bulk crystal, unable to contact the substrate molecules, thus exhibiting extremely low catalytic performance.

[0132] The structural guidance role of functionalized hierarchical salt templates is key to enhancing catalytic activity. The catalytic activity of Comparative Example D3 (unfunctionalized single template) was significantly lower than that of Example S1, demonstrating that the introduction of the PAdAAm polymer brush on the template surface guides the formation of a two-dimensional nanosheet structure of γ-CD-MOF through host-guest interactions, greatly increasing the exposure of active sites. Comparing Comparative Example D5 (functionalized single template) with Example S1, the latter exhibited higher catalytic activity. This indicates that hierarchical template structures have advantages in forming high-quality, highly dispersed nanosheets, more effectively preventing nanosheet stacking during exfoliation and post-processing, thereby maintaining higher accessibility to active sites.

[0133] The catalytic performance of the material was further optimized by the assisted growth of an external physical field. The catalytic activity of Comparative Example D4 (without field assistance) was significantly lower than that of Examples S1 (ultrasonic field assistance) and S3 (electric field assistance), with S3 exhibiting the highest activity. This indicates that the application of an external field, by modulating crystallization kinetics, promotes the formation of thinner, less defective, or more regularly shaped two-dimensional nanosheets, thereby maximizing the number of accessible γ-cyclodextrin active sites per unit mass of material.

[0134] Comprehensive analysis shows that the preparation strategy proposed in this invention, which combines functionalized multi-level salt templates with external physical fields, is the decisive factor in obtaining highly catalytically active γ-CD-MOF nanosheets. This strategy, through precise control of the microstructure and structure of the material, directly translates into improved macroscopic performance, that is, maximizing the exposure of functional active sites, thus exhibiting significant advantages in catalytic applications.

Claims

1. A method for preparing a salt template for two-dimensional γ-cyclodextrin MOF nanosheets, characterized in that, Includes the following steps: S1. Provision of a functionalized multilevel salt template: A functionalized multilevel salt template with a polymer brush grafted on its surface having an affinity for γ-cyclodextrin is provided; S2. Preparation and loading of precursor solution: Prepare a precursor solution containing γ-cyclodextrin and base, and load the precursor solution onto the functionalized multi-level salt template; S3. Growth reaction: Under preset conditions, a growth reaction is carried out to grow γ-cyclodextrin MOF in situ on the surface of the functionalized multi-level salt template to form a γ-cyclodextrin MOF@multi-level salt template complex. S4. Removal of primary template: The γ-cyclodextrin MOF@multi-level salt template complex is treated with a first selective solvent to dissolve and remove the primary salt template contained in the γ-cyclodextrin MOF@multi-level salt template complex. S5. Exfoliation of two-dimensional nanosheets: The γ-cyclodextrin MOF@multi-level salt template complex after step S4 is dispersed in a second solvent, and the γ-cyclodextrin MOF nanosheets are exfoliated from the surface of the secondary salt template by ultrasonic treatment. S6. Separation and purification of nanosheets: The exfoliated γ-cyclodextrin MOF nanosheets are separated from the suspension and purified by separation and washing techniques; S7. Drying of nanosheets: The purified γ-cyclodextrin MOF nanosheets are dried to obtain two-dimensional γ-cyclodextrin MOF nanosheet products.

2. The method for preparing a salt template for two-dimensional γ-cyclodextrin MOF nanosheets according to claim 1, characterized in that, The method for preparing the functionalized multi-level salt template includes: A multi-level salt template is assembled by mixing primary salt template crystals with larger particle sizes with secondary salt template crystals with smaller particle sizes. The polymer anchoring initiator is fixed to the surface of the multi-level salt template; A polymer brush with affinity for γ-cyclodextrin is grafted onto the anchoring initiator via a surface-initiated polymerization reaction.

3. The method for preparing a salt template for two-dimensional γ-cyclodextrin MOF nanosheets according to claim 1, characterized in that, In the precursor solution, the molar ratio of γ-cyclodextrin to base is 1:(6-12).

4. The method for preparing a salt template for two-dimensional γ-cyclodextrin MOF nanosheets according to claim 1, characterized in that, The conditions for the growth reaction include reacting at a temperature of 20-70°C for 6-48 hours.

5. The method for preparing a salt template for two-dimensional γ-cyclodextrin MOF nanosheets according to claim 4, characterized in that, During the growth reaction, an external physical field is applied, which is an ultrasonic field or a direct current electric field.

6. The method for preparing a salt template for two-dimensional γ-cyclodextrin MOF nanosheets according to claim 1, characterized in that, The first selective solvent is tetrahydrofuran, and the second solvent is methanol.

7. The application of salt templates for two-dimensional γ-cyclodextrin MOF nanosheets, characterized in that, Application of the two-dimensional γ-cyclodextrin MOF nanosheets in the preparation of materials for catalysis, adsorption or separation.

8. The application of the salt template of the two-dimensional γ-cyclodextrin MOF nanosheets according to claim 7, characterized in that, The material used for catalysis, adsorption, or separation is a catalytic material, and the application is catalytic ester hydrolysis reaction.

9. The application of the salt template of the two-dimensional γ-cyclodextrin MOF nanosheets according to claim 7, characterized in that, The two-dimensional γ-cyclodextrin MOF nanosheets have uniform nanoscale thickness and good structural integrity.

10. The application of the salt template of the two-dimensional γ-cyclodextrin MOF nanosheets according to claim 7, characterized in that, The material used for catalysis, adsorption, or separation is also a membrane material or an adsorbent material.

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