Cyclodextrin covalent organic framework material as well as preparation method and application thereof

Abstract

The invention relates to a cyclodextrin covalent organic framework material as well as a preparation method and catalytic application thereof, and belongs to the technical field of porous organic materials. Firstly, a cyclodextrin-based precursor with a clear ordered structure is constructed through supramolecular self-assembly or metal coordination, an ordered framework is taken as a template, a fluorobenzene monomer cross-linking agent is introduced, efficient enrichment is carried out by utilizing developed pore channels of the precursor, local reaction concentration is remarkably improved, and the preparation method is simple and easy to implement. And then ether bond connection with high bond energy is formed through an irreversible aromatic nucleophilic substitution reaction, and finally conversion from a weak interaction framework to crystalline gamma-CD-COF connected by a covalent bond is realized. According to the preparation method, the orderliness advantage of supramolecular preassembly and the stability characteristic of irreversible covalent bonds are combined, and the prepared gamma-CD-COF not only has high crystallinity, high specific surface area and pore channels, but also shows excellent water-phase stability.

Description

Technical Field

[0001] This invention relates to a cyclodextrin covalent organic framework material, its preparation method, and its catalytic application, belonging to the field of porous organic materials technology. Background Technology

[0002] Cyclodextrins are an important class of artificial enzymes, exhibiting significant application potential in catalysis due to their unique cavity structure and abundant hydroxyl groups. The cavities of cyclodextrins can selectively encapsulate guest molecules, forming intermolecular hydrogen bonds, catalyzing a variety of chemical reactions, and also possess advantages such as low cost, easy availability, non-toxicity, and good biocompatibility. However, unmodified cyclodextrins face some challenges in practical catalytic applications: 1. Difficulty in recovery: cyclodextrins are difficult to separate and reuse in homogeneous catalytic systems; 2. Limited catalytic activity: poor cavity accessibility limits substrate mass transfer; 3. Structural disorder: cyclodextrins are arranged disorderedly in amorphous polymers, resulting in insufficient cavity exposure and unclear structure-activity relationships.

[0003] Researchers have attempted to modify cyclodextrins onto different supports or synthesize cyclodextrin-based polymers to improve the stability and recyclability of catalytic processes. Professor Dichtel's team synthesized an amorphous porous polymer (P-CDPs) by crosslinking β-cyclodextrin with tetrafluoroterephthalonitrile. P-CDPs exhibit good chemical stability, resisting acids and various organic solvents, and can be used for the rapid adsorption of organic pollutants in water (Nature 2016, 529, 190-194). Dina Murtinho's group prepared β-CD molecular sponges and used them to catalyze the metal-free Henry and Knoevenagel reactions between aromatic aldehydes and nitromethane or ethyl cyanoacetate, achieving conversion rates of 90% in both cases (Carbohydr. Polym. 2024, 326, 121612–121624). However, the disordered arrangement of cyclodextrins in these materials makes it difficult to expose some cavities, hindering substrate mass transfer and affecting catalytic performance. Furthermore, the structural disorder limits the establishment of precise structure-activity relationships. Constructing stable cyclodextrin-based COFs using cyclodextrin as building blocks promises to leverage the well-defined and ordered structure and extensive pores of COFs to achieve ordered arrangement of cyclodextrin molecules, promoting mass transfer and facilitating recovery. The inventors' research group previously reported an anionic CD-COF-Li material prepared by reacting γ-CD with trimethyl borate. This material exhibits high ionic conductivity and can be used as a solid electrolyte in lithium batteries (Angew. Chem. Int. Ed. 2017, 56, 16313-16317). Feng Yuqi's research group prepared β-CD-COF using modified β-CD and terephthalaldehyde as reactants, adjusting different proportions of water and ethanol as solvents, and adding acetic acid as a catalyst, achieving highly efficient removal of trace pollutants from water (Chem. Eur. J. 2018, 24, 10979-10983).

[0004] However, modifying cyclodextrins onto different support surfaces or constructing cyclodextrin-based polymer materials have mitigated the difficulty in recycling to some extent. Cyclodextrin molecules often exhibit disordered arrangement during immobilization, causing some cavities to be obscured or difficult to fully expose, which may hinder mass transfer and access to the reaction substrate, ultimately affecting its catalytic efficiency.

[0005] Introducing cyclodextrins into stable, ordered porous frameworks not only facilitates recycling and reuse but also promotes substrate enrichment and mass transfer, thereby improving catalytic efficiency. Copolymer-containing porous materials (COFs), as a class of crystalline porous materials, possess well-defined and ordered structures with regular and well-developed pores. Constructing stable COFs using cyclodextrins allows for adjustment of the cyclodextrin stacking pattern, thus controlling the accessibility of the pores and simultaneously promoting substrate enrichment and mass transfer during catalysis, thereby improving catalytic efficiency. However, introducing aliphatic flexible cyclodextrin units into COF systems increases structural complexity and synthetic difficulty. Existing CD-COFs are mostly based on reversible covalent bonds (such as borate esters and imine bonds), which are easily degraded in complex catalytic environments; their synthesis requires high temperature, high pressure, and anhydrous and oxygen-free conditions, making mild and large-scale preparation difficult; amorphous polymers or low-crystallinity COFs are not conducive to substrate mass transfer and structure-activity relationship studies. Therefore, there is an urgent need to develop synthetic strategies to prepare cyclodextrin COF materials that combine high specific surface area, excellent stability, and uniform pore structure. Summary of the Invention

[0006] This invention aims to address the prevalent problems of structural disorder, insufficient stability, and low mass transfer efficiency in existing cyclodextrin-based materials. It proposes a cyclodextrin covalent organic framework material, its preparation method, and its catalytic applications. The "crystallization" and "bonding" processes are separated: firstly, a cyclodextrin-based precursor (γ-CD-Crystal or γ-CD-MOF) with a well-defined ordered structure is constructed through supramolecular self-assembly or metal coordination, achieving a regular spatial arrangement of cyclodextrin units. Using this ordered framework as a template, a fluorobenzene monomer crosslinking agent is further introduced. The precursor's well-developed pores efficiently enrich the crosslinking agent, significantly increasing the local reaction concentration. Then, through irreversible aromatic nucleophilic substitution reactions, high-bond-energy ether bonds are formed, ultimately achieving the transformation from a weakly interacting framework to a covalently bonded crystalline γ-CD-COF. This invention combines the ordered advantages of supramolecular preassembly with the stable characteristics of irreversible covalent bonds. The prepared γ-CD-COF not only possesses high crystallinity, high specific surface area, and pores, but also exhibits excellent aqueous phase stability, providing an ideal platform for the efficient utilization of cyclodextrin cavities and substrate mass transfer. Furthermore, this method can achieve gram-scale preparation under ambient pressure, avoiding the dependence on anhydrous, oxygen-free, high-temperature, and high-pressure conditions in traditional COF synthesis, thus laying a solid foundation for the large-scale preparation and application of high-performance cyclodextrin-based catalytic materials.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows.

[0008] A method for preparing a cyclodextrin covalent organic framework material, comprising the following steps: (1) Dissolve γ-cyclodextrin (γ-CD) in the first organic solvent and mix well to obtain a homogeneous solution. Heat the solution to prepare γ-CD crystals (γ-CD-Crystal). Alternatively, γ-cyclodextrin (γ-CD) and a strong base are dissolved in deionized water, the aqueous solution is filtered, and the vapor of the first organic solvent is diffused into the solution. After 3 to 7 days, colorless and transparent crystals are generated. After the reaction is completed, the crystals are centrifuged, washed, and dried under vacuum to obtain γ-CD-MOF. (2) Add catalyst, fluorobenzene monomer and second organic solvent to γ-CD crystal or γ-CD-MOF, heat at above 80°C for more than 4 days, centrifuge and wash after the reaction, and then vacuum dry to obtain cyclodextrin covalent organic framework material (γ-CD-COF).

[0009] Further, in step (1), the first organic solvent includes N,N-dimethylformamide (DMF) or methanol.

[0010] Furthermore, in step (1), the heating reaction is carried out at 85~100℃ for more than 30 hours.

[0011] Further, in step (1), the strong base is potassium hydroxide (KOH); the molar ratio of γ-CD to potassium hydroxide is 1:8.

[0012] Further, in step (2), the catalyst is potassium carbonate (K2CO3).

[0013] Further, in step (2), the fluorobenzene monomer includes tetrafluoroterephthalonitrile, decafluorobiphenyl, 2,6-difluoroterephthalonitrile, 2,5-difluoroterephthalonitrile, and 2,3-difluoroterephthalonitrile; the second organic solvent includes mesitylene and N,N-dimethylformamide (DMF).

[0014] Further, in step (2), the molar ratio of the γ-CD crystal or γ-CD-MOF, catalyst, and fluorobenzene monomer is 1:8~16:2.27.

[0015] Furthermore, in step (2), the reaction is heated at 85~100℃ for 4~5 days.

[0016] Furthermore, in steps (1) and (2), the washing process involves rinsing with water, N,N-dimethylformamide (DMF), and tetrahydrofuran (THF) in sequence.

[0017] A cyclodextrin covalent organic framework material was prepared by the above method.

[0018] An application of a cyclodextrin covalent organic framework material, wherein the material is used as a heterogeneous catalyst in host-guest interaction driven catalytic reactions.

[0019] Beneficial effects (1) By using a pre-assembly strategy, a crystalline precursor (γ-CD-Crystal or γ-CD-MOF) with a regular arrangement of cyclodextrin units is first constructed, which lays the foundation for the long-range ordered structure of the final COF material. The disordered cyclodextrin is transformed into well-crystallized γ-CD-COF, which provides abundant accessible active sites and efficient mass transfer channels for substrate molecules.

[0020] (2) The irreversible aromatic nucleophilic substitution reaction is used to form a high-bond-energy ether bond, which overcomes the limitation of poor stability of CD-COF with dynamic covalent bonds such as boron ester bonds in aqueous phase and harsh chemical environments. The obtained γ-CD-F-COF can maintain the integrity of structure and morphology in water, which makes it advantageous for applications in green catalysis, water treatment and other fields.

[0021] (3) In the oxidation of cinnamaldehyde, γ-CD-F-COF exhibited superior catalytic activity and selectivity compared to γ-CD and amorphous materials (γ-CD-COP), increasing the benzaldehyde yield to 82%. Its porous framework not only enriches the substrate but also lowers the reaction energy barrier and accelerates the reaction rate through multiple weak interactions (hydrogen bonds, π-π interactions) with the substrate. As a heterogeneous catalyst, γ-CD-F-COF can be recovered through simple filtration and maintains high catalytic efficiency even after four consecutive uses, demonstrating good reusability and economy.

[0022] (4) The "pre-assembly-post-crosslinking" strategy proposed in this invention separates the construction of ordered structures from the formation of stable covalent bonds, providing a new approach to solving the problem of constructing highly crystalline COFs from flexible macromolecules. This strategy is applicable to both supramolecular interactions (γ-CD-Crystal) and metal coordination interactions (γ-CD-MOF) as pre-assembly precursors, demonstrating good versatility. The synthesis process does not require strict anhydrous and oxygen-free conditions or high-temperature and high-pressure equipment, and can achieve gram-scale preparation under normal pressure, significantly reducing the difficulty of operation and production costs, which is conducive to promoting the practical application of COF materials.

[0023] (5) The ordered structure of the material is conducive to in-depth research on substrate mass transfer behavior and catalytic mechanism. Through kinetic tests, spectroscopic characterization and other means, the key role of porous framework in substrate enrichment and reduction of reaction activation energy was clarified, providing a theoretical basis for the design of high-performance artificial enzyme catalysts. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the pre-assembly strategy for preparing γ-CD-COF in this invention.

[0025] Figure 2The diagram shows the morphology, crystallinity, and specific surface area of ​​γ-CD-Crystal prepared in step (1) of Example 1. a and b are morphological comparisons before and after adding water, c is the powder X-ray diffraction pattern of γ-CD-Crystal, and d is the N2 adsorption-desorption isotherm curve of γ-CD-Crystal.

[0026] Figure 3 The morphology, crystallinity, specific surface area, and pore size distribution of γ-CD-F-COF prepared in step (2) of Example 1 are shown in the diagram. Among them, a and b are the morphology comparison before and after adding water, c is the powder X-ray diffraction pattern of γ-CD-F-COF, d is the N2 adsorption-desorption isotherm curve of γ-CD-F-COF, and e is the pore size distribution diagram.

[0027] Figure 4 The diagram shows the morphology, crystallinity, and specific surface area of ​​the γ-CD-MOF prepared in step (1) of Example 2. In the diagram, a and b represent the morphology comparison before and after adding water, c is the powder X-ray diffraction pattern of γ-CD-MOF, d is the N2 adsorption-desorption isotherm curve of γ-CD-MOF, and e is the pore size distribution diagram.

[0028] Figure 5 The morphology, crystallinity, specific surface area, and pore size distribution of γ-CD-F-COF prepared in step (2) of Example 2 are shown in the diagram. Among them, a and b are the morphology comparison before and after adding water, c is the powder X-ray diffraction pattern of γ-CD-F-COF, d is the N2 adsorption-desorption isotherm curve of γ-CD-F-COF, and e is the pore size distribution diagram.

[0029] Figure 6 The crystallinity, specific surface area, and pore size distribution of γ-CD-OF-COF prepared in step (2) of Example 3 are shown in the diagram. Among them, a is the powder X-ray diffraction pattern of γ-CD-OF-COF, b is the N2 adsorption-desorption isotherm of γ-CD-OF-COF, and c is the pore size distribution diagram.

[0030] Figure 7 The crystallinity, specific surface area, and pore size distribution of γ-CD-MF-COF prepared in step (2) of Example 4 are shown in the diagram. Among them, a is the powder X-ray diffraction pattern of γ-CD-MF-COF, b is the N2 adsorption-desorption isotherm of γ-CD-MF-COF, and c is the pore size distribution diagram.

[0031] Figure 8 The crystallinity, specific surface area, and pore size distribution of γ-CD-PF-COF prepared in step (2) of Example 5 are shown in the diagram. Among them, a is the powder X-ray diffraction pattern of γ-CD-PF-COF, b is the N2 adsorption-desorption isotherm of γ-CD-PF-COF, and c is the pore size distribution diagram.

[0032] Figure 9 The crystallinity, specific surface area, and pore size distribution of γ-CD-F-COF prepared in step (2) of Example 6 are shown in the diagram. Among them, a is the powder X-ray diffraction pattern of γ-CD-F-COF, b is the N2 adsorption-desorption isotherm of γ-CD-F-COF, and c is the pore size distribution diagram.

[0033] Figure 10 The crystallinity, specific surface area, and pore size distribution of γ-CD-F-COP prepared in step 1 of Comparative Example are shown in the diagram. In the diagram, a is the powder X-ray diffraction pattern of γ-CD-F-COP, and b is the N2 adsorption-desorption isotherm of γ-CD-F-COP.

[0034] Figure 11 This is a schematic diagram of the γ-CD-F-COF catalytic oxidation of cinnamaldehyde to benzaldehyde in Example 7. In the diagram, a represents the reaction expression, b represents the yield of benzaldehyde produced by different materials, and c represents the cycle test. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments.

[0036] Example 1 γ-CD-F-COF prepared based on γ-CD-Crystal (1) First, add γ-CD (0.1297 g, 0.10 mmol) to a 20 mL vial, add 5 mL of N,N-dimethylformamide (DMF), and then slowly add 8.0 mL of methanol. Shake the vial up and down and seal it. Place it in a Yamato oven and set the temperature program as follows: raise the temperature from room temperature to 85 °C in 1 hour, keep the temperature at 85 °C for 31 hours, and after the reaction is completed, lower the temperature from 85 °C to room temperature in 1 hour to obtain γ-CD-Crystal.

[0037] (2) The supernatant of the prepared γ-CD-Crystal was aspirated, and anhydrous potassium carbonate (0.220 g, 1.60 mmol) and tetrafluoroterephthalonitrile (0.0455 g, 0.227 mmol) were added. 8.0 mL of mesitylene and 4.0 mL of N,N-dimethylformamide (DMF) were also added. The mixture was reacted in a Yamato oven at 85 °C for 5 days to obtain a pale yellow powder. The powder was washed twice with water, N,N-dimethylformamide (DMF), and tetrahydrofuran (THF), and then dried under vacuum at 60 °C to obtain γ-CD-F-COF.

[0038] Example 2 γ-CD-F-COF prepared based on γ-CD-MOF (1) First, add γ-CD (1.30 g, 1 mmol) and potassium hydroxide (450 mg, 8 mmol) to a 20 mL vial, and add 20 mL of deionized water. Filter the aqueous solution and allow methanol vapor (about 50 mL) to diffuse into the solution. After 3-7 days, colorless transparent crystals are formed in the vial. Wash with methanol three times and dry under vacuum at room temperature to obtain γ-CD-MOF.

[0039] (2) Weigh 0.1445 g of γ-CD-MOF material, add anhydrous potassium carbonate (0.220 g, 1.60 mmol) and tetrafluoroterephthalonitrile (0.0455 g, 0.227 mmol), add 8.0 mL of mesitylene and 4.0 mL of N,N-dimethylformamide (DMF). In a Yamato oven, react at 85 °C for 5 days to obtain a pale yellow powder. Wash twice with water, N,N-dimethylformamide (DMF) and tetrahydrofuran (THF), respectively, and dry under vacuum at 60 °C to obtain γ-CD-F-COF.

[0040] Example 3 γ-CD-OF-COF prepared based on γ-CD-MOF (1) Synthesis of 2,3-difluoroterephthalonitrile: (0.5 g, 2.4 mmol) and 10 mL of thionyl chloride were refluxed and stirred at 80 °C for 12 h. After cooling to room temperature, the solvent was evaporated, and the product was dissolved in dry chloroform or dichloromethane (6 mL). 28% ammonia water (6 mL) was added dropwise at 5 °C, and stirring was continued for 0.5 h (appropriate extension). After extraction with chloroform or dichloromethane, the organic phase was dried with sodium sulfate, filtered, and evaporated to dryness. The product was added to 4 mL of phosphorus oxychloride, stirred at 80 °C for 2 h, cooled to room temperature, and the solvent was evaporated. The product was stirred in diethyl ether (10 mL) and water (6 mL) for 0.5 h, extracted with diethyl ether, washed with brine, dried with sodium sulfate, and the organic phase was evaporated to dryness.

[0041] (2) First, add γ-CD (1.30 g, 1 mmol) and potassium hydroxide (450 mg, 8 mmol) to a 20 mL vial, and add 20 mL of deionized water. Filter the aqueous solution and allow methanol vapor (about 50 mL) to diffuse into the solution. After 3-7 days, colorless transparent crystals are formed in the vial. Wash with methanol three times and dry under vacuum at room temperature to obtain γ-CD-MOF.

[0042] (3) Weigh 0.1445 g of γ-CD-MOF material, add anhydrous potassium carbonate (0.220 g, 1.60 mmol), 2,3-difluoroterephthalonitrile (0.037 g, 0.227 mmol), 8.0 mL of mesitylene, and 4.0 mL of N,N-dimethylformamide (DMF). In a Yamato oven, react at 85 °C for 5 days to obtain a pale yellow powder. Wash twice with water, N,N-dimethylformamide (DMF), and tetrahydrofuran (THF), and dry under vacuum at 60 °C to obtain γ-CD-OF-COF.

[0043] Example 4 γ-CD-MF-COF prepared based on γ-CD-MOF (1) First, add γ-CD (1.30 g, 1 mmol) and potassium hydroxide (450 mg, 8 mmol) to a 20 mL vial, and add 20 mL of deionized water. Filter the aqueous solution and allow methanol vapor (about 50 mL) to diffuse into the solution. After 3-7 days, colorless transparent crystals are formed in the vial. Wash with methanol three times and dry under vacuum at room temperature to obtain γ-CD-MOF.

[0044] (2) Weigh 0.1445 g of γ-CD-MOF material, add anhydrous potassium carbonate (0.220 g, 1.60 mmol), 2,6-difluoroterephthalonitrile (0.037 g, 0.227 mmol), 8.0 mL of mesitylene, and 4.0 mL of N,N-dimethylformamide (DMF). In a Yamato oven, react at 85 °C for 5 days to obtain a pale yellow powder. Wash twice with water, N,N-dimethylformamide (DMF), and tetrahydrofuran (THF), and dry under vacuum at 60 °C to obtain γ-CD-MF-COF.

[0045] Example 5 γ-CD-PF-COF prepared based on γ-CD-MOF (1) First, add γ-CD (1.30 g, 1 mmol) and potassium hydroxide (450 mg, 8 mmol) to a 20 mL vial, and add 20 mL of deionized water. Filter the aqueous solution and allow methanol vapor (about 50 mL) to diffuse into the solution. After 3-7 days, colorless transparent crystals are formed in the vial. Wash with methanol three times and dry under vacuum at room temperature to obtain γ-CD-MOF.

[0046] (2) Weigh 0.1445 g of γ-CD-MOF material, add anhydrous potassium carbonate (0.220 g, 1.60 mmol), 2,5-difluoroterephthalonitrile (0.037 g, 0.227 mmol), 8.0 mL of mesitylene, and 4.0 mL of N,N-dimethylformamide (DMF). In a Yamato oven, react at 85 °C for 5 days to obtain a pale yellow powder. Wash twice with water, N,N-dimethylformamide (DMF), and tetrahydrofuran (THF), and dry under vacuum at 60 °C to obtain γ-CD-PF-COF.

[0047] Example 6 Gram-scale preparation of γ-CD-F-COF based on γ-CD-Crystal (1) First, add γ-CD (1.297 g, 1 mmol) to a 250 mL Shu Niu bottle, add 50 mL of N,N-dimethylformamide (DMF), and then slowly add 80 mL of methanol. Shake the bottle and seal it. Place it in a Yamato oven with the temperature program set as follows: increase the temperature from room temperature to 85 °C in 1 hour, and keep the temperature at 85 °C for 31 hours. After the reaction is completed, reduce the temperature from 85 °C to room temperature in 1 hour to obtain γ-CD-Crystal.

[0048] (2) The supernatant of the prepared γ-CD-Crystal was aspirated, and anhydrous potassium carbonate (2.2 g, 16 mmol) and tetrafluoroterephthalonitrile (0.455 g, 2.27 mmol) were added. 80 mL of mesitylene and 40 mL of N,N-dimethylformamide (DMF) were also added. The mixture was reacted in a Yamato oven at 85 °C for 5 days to obtain a pale yellow powder. The powder was washed twice with water, N,N-dimethylformamide (DMF), and tetrahydrofuran (THF), and then dried under vacuum at 60 °C to obtain γ-CD-F-COF.

[0049] Example 7 γ-CD-F-COF was used in experiments to catalyze the oxidation of cinnamaldehyde to benzaldehyde. In a 100 mL three-necked flask equipped with a reflux condenser and a heating stirrer, 1 mmol of cinnamaldehyde (0.1322 g) was dissolved in 25 mL of deionized water at 60 °C. Then, activated γ-CD-F-COF (8.5 mg), 1.5 mmol of sodium carbonate (0.1590 g), and 2 mL of 30% hydrogen peroxide were added. The mixture was stirred for 30 minutes, and the reaction mixture was extracted with 50 mL of ethyl acetate to obtain an organic phase containing benzaldehyde, which was then analyzed by gas chromatography-mass spectrometry (GC-MS). The experiment was repeated by replacing γ-CD-F-COF with γ-CD (6.5 mg) and γ-CD-F-COP (8.5 mg), keeping all other conditions unchanged.

[0050] Comparative Example 1 Preparation of γ-CD-F-COP γ-CD (0.1297 g, 0.10 mmol), anhydrous potassium carbonate (0.220 g, 1.60 mmol), and tetrafluoroterephthalonitrile (0.0455 g, 0.227 mmol) were weighed into 20 mL vials, and 8.0 mL of mesitylene and 4.0 mL of N,N-dimethylformamide (DMF) were added. The mixture was reacted in a Yamato oven at 85 °C for 5 days to obtain a pale yellow powder. The powder was washed twice with water, N,N-dimethylformamide (DMF), and tetrahydrofuran (THF), and then dried under vacuum at 60 °C to obtain γ-CD-F-COP.

[0051] Structural and performance characterization (1) The present invention proposes a method for synthesizing cyclodextrin covalent organic frameworks based on a pre-assembly strategy. Schematic diagram is shown below. Figure 1 As shown, this method first constructs an ordered cyclodextrin precursor (γ-CD-Crystal or γ-CD-MOF) through supramolecular self-assembly or metal coordination. Then, using the precursor as a template, the ordered channels are used to enrich the fluorobenzene monomer crosslinking agent. Finally, ether bonds are formed through aromatic nucleophilic substitution reactions, successfully transforming the weakly interacting framework into a covalently linked crystalline γ-CD-COF. It can be seen that, compared with the pre-assembly strategy described in this invention, the traditional solvothermal synthesis method directly mixes and reacts cyclodextrin and crosslinking agent in a solvent, resulting in an amorphous polymer (γ-CD-F-COP). This disordered structure leads to blockage of the cyclodextrin cavities, severely limiting substrate mass transfer and catalytic performance.

[0052] (2) The morphology of the γ-CD-Crystal prepared in Example 1 was characterized by optical microscopy, such as... Figure 2a and 2b show the morphology before and after adding water, respectively. The prepared γ-CD-Crystal exhibits a regular square crystal morphology and dissolves rapidly in the aqueous phase, with its morphology changing significantly within a short period. Powder X-ray diffraction (PXRD) was used to characterize the phase of the γ-CD-Crystal prepared in Example 1, and the test results are as follows: Figure 2 As shown in c, the changes in the diffraction peaks indicate a change in the stacking pattern of the cyclodextrin units. The N2 adsorption / desorption isotherm of the γ-CD-Crystal prepared in Example 1 was collected at 77 K, as shown in... Figure 2 As shown in d, the gas adsorption capacity of γ-CD-Crystal is extremely low. It is speculated that due to the weak supramolecular linkages in γ-CD-Crystal, the framework collapses after removing solvent molecules during activation.

[0053] (3) The morphology of the γ-CD-F-COF prepared in Example 1 was characterized by optical microscopy, such as... Figure 3 a and 3b show the morphology before and after adding water, respectively. The prepared γ-CD-F-COF exhibits a regular square crystal morphology, which is maintained in the aqueous phase, demonstrating its excellent water stability. Powder X-ray diffraction (PXRD) was used to characterize the phase of the γ-CD-F-COF prepared in Example 1, and the test results are as follows: Figure 3 As shown in c, the changes in diffraction peaks indicate a change in the stacking pattern of the cyclodextrin units. γ-CD-F-COF exhibits strong diffraction peaks at 4.0°, 5.6°, 6.9°, and 8.0°, which can be attributed to the (110), (200), (211), and (220) crystal planes, respectively. The N2 adsorption / desorption isotherm of γ-CD-F-COF prepared in Example 1 was collected at 77 K, as shown in... Figure 3 As shown in d, the specific surface area of ​​γ-CD-F-COF is calculated to be 880 m². 2 g -1 ,like Figure 3 As shown in Figure e, the pore size distribution of γ-CD-F-COF is calculated based on nonlinear density functional theory, and the pore size is approximately 1.7 nm.

[0054] The characterization results in (2) and (3) above demonstrate that the weakly interacting γ-CD-Crystal successfully transformed into the covalently connected stable γ-CD-F-COF, proving the feasibility of the pre-assembly strategy.

[0055] (4) The morphology of the γ-CD-MOF prepared in Example 2 was characterized by optical microscopy, such as... Figure 4a and 4b show the morphology before and after adding water, respectively. The prepared γ-CD-MOF exhibits a regular square crystal morphology and dissolves rapidly in the aqueous phase, with its morphology changing significantly within a short period. Powder X-ray diffraction (PXRD) was used to characterize the phase of the γ-CD-MOF prepared in Example 2, and the test results are as follows: Figure 4 As shown in Figure c, the PXRD pattern of γ-CD-MOF matches the simulated value, confirming the successful synthesis of γ-CD-MOF. By comparing the PXRD patterns of the cyclodextrin monomer and γ-CD-MOF, changes in diffraction peaks were observed, indicating a change in the stacking mode of cyclodextrin units within the γ-CD-MOF framework. The N2 adsorption / desorption isotherm of the γ-CD-MOF prepared in Example 2 was collected at 77 K, as shown in Figure c. Figure 4 As shown in d, the specific surface area calculated by the BET model is 1200 m². 2 g -1 According to calculations based on nonlinear density functional theory, the pore size is mainly distributed at 1.7 nm.

[0056] (5) The morphology of the γ-CD-F-COF prepared in Example 2 was characterized by optical microscopy, such as... Figure 5 a and 5b show the morphology before and after adding water, respectively. The prepared γ-CD-COF exhibits a regular square crystal morphology, which is maintained in the aqueous phase. This indicates a significant difference in stability between the prepared γ-CD-F-COF and γ-CD-MOF, preliminarily demonstrating successful crosslinking. Powder X-ray diffraction (PXRD) was used to characterize the phase of the γ-CD-COF prepared in Example 2. The test results are as follows: Figure 5 As shown in c, the changes in diffraction peaks indicate a change in the stacking mode of the cyclodextrin units. γ-CD-F-COF exhibits strong diffraction peaks at 4.0°, 5.6°, 6.9°, and 8.0°, which can be attributed to the (110), (200), (211), and (220) crystal planes, respectively. The N2 adsorption / desorption isotherms of the γ-CD-MOF prepared in Example 2 were collected at 77 K, as shown in... Figure 5 As shown in d, the specific surface area of ​​γ-CD-F-COF is calculated to be 886 m². 2 g -1 ,like Figure 5 As shown in Figure e, the pore size distribution of γ-CD-F-COF is calculated based on nonlinear density functional theory, and the pore size is approximately 1.7 nm.

[0057] The characterization results in (4) and (5) above demonstrate that the weakly interacting γ-CD-MOF successfully transformed into the covalently connected stable γ-CD-F-COF, proving the feasibility of the pre-assembly strategy.

[0058] (6) To further verify the universality of this strategy, different fluorobenzene monomers were used as crosslinking agents, including but not limited to 2,6-difluoroterephthalonitrile, 2,5-difluoroterephthalonitrile, and 2,3-difluoroterephthalonitrile. The γ-CD-OF-COF prepared in Example 3 was characterized by powder X-ray diffraction (PXRD), and the test results are as follows: Figure 6 As shown in figure a, the strong diffraction peaks indicate that the material has high crystallinity. The N2 adsorption / desorption isotherm of the γ-CD-OF-COF prepared in Example 3 was collected at 77 K, as shown in figure a. Figure 6 As shown in b, the specific surface area of ​​γ-CD-OF-COF is calculated to be 125 m². 2 g -1 ,like Figure 6 As shown in Figure c, the pore size distribution of γ-CD-OF-COF is calculated based on nonlinear density functional theory, and the pore size is approximately 1.5 nm.

[0059] (7) The γ-CD-MF-COF prepared in Example 4 was characterized by powder X-ray diffraction (PXRD). The test results are as follows: Figure 7 As shown in figure a, the strong diffraction peaks indicate that the material has high crystallinity. The N2 adsorption / desorption isotherm of the γ-CD-MF-COF prepared in Example 4 was collected at 77 K, as shown in figure a. Figure 7 As shown in b, the specific surface area of ​​γ-CD-MF-COF is calculated to be 150 m². 2 g -1 ,like Figure 7 As shown in Figure c, the pore size distribution of γ-CD-MF-COF is calculated based on nonlinear density functional theory, and the pore size is approximately 1.6 nm.

[0060] (8) The γ-CD-PF-COF prepared in Example 5 was characterized by powder X-ray diffraction (PXRD). The test results are as follows: Figure 8 As shown in figure a, the strong diffraction peaks indicate that the material has high crystallinity. The N2 adsorption / desorption isotherm of the γ-CD-PF-COF prepared in Example 5 was collected at 77 K, as shown in figure a. Figure 8 As shown in b, the specific surface area of ​​γ-CD-PF-COF is calculated to be 108 m². 2 g -1 ,like Figure 8 As shown in Figure c, the pore size distribution of γ-CD-PF-COF is calculated based on nonlinear density functional theory, and the pore size is approximately 1.7 nm.

[0061] The characterization results in (6) to (8) above demonstrate the universality of the pre-assembly strategy.

[0062] (9) Using a pre-assembly method, taking γ-CD-Crystal as an example, gram-scale preparation was successfully achieved under normal pressure by proportionally increasing the monomer and solvent ratio. The γ-CD-F-COF prepared in Example 6 was characterized by powder X-ray diffraction (PXRD), and the test results are as follows: Figure 9 As shown in figure a, the strong diffraction peaks indicate that the material has high crystallinity. The N2 adsorption / desorption isotherm of the γ-CD-F-COF prepared in Example 6 was collected at 77 K, as shown in figure a. Figure 9 As shown in b, the specific surface area of ​​γ-CD-F-COF is calculated to be 850 m². 2 g -1 ,like Figure 9 As shown in Figure c, the pore size distribution of γ-CD-F-COF was calculated based on nonlinear density functional theory, and the pore size is also approximately 1.7 nm. Experimental results show that this method can achieve gram-scale preparation of γ-CD-F-COF.

[0063] (10) To verify the superiority of the pre-assembly method described in this invention, a control experiment was conducted using a traditional solvothermal method: γ-CD, tetrafluoroterephthalonitrile, and potassium carbonate were directly mixed in the same solvent system at the same reaction temperature and time. The phase characterization of the γ-CD-F-COP prepared in Comparative Example 1 was performed using powder X-ray diffraction (PXRD), and the test results are as follows: Figure 10 As shown in Figure a, its powder X-ray diffraction pattern exhibits a large bulge, indicating that it is an amorphous material. The N2 adsorption / desorption isotherm of γ-CD-F-COP prepared in Comparative Example 1 was collected at 77 K, as shown in Figure a. Figure 10 As shown in b, the nitrogen adsorption test shows that its specific surface area is negligible, confirming that its pore structure is blocked.

[0064] (11) Based on the water stability, well-developed pores, and host-guest interaction of γ-CD-F-COF and its cyclodextrin unit, it was used as a catalyst in the oxidation of cinnamaldehyde to benzaldehyde. The reaction process is as follows: Figure 11 As shown in figure a, its catalytic performance was studied. Figure 11 As shown in b, comparing the catalytic performance of γ-CD, γ-CD-F-COF, and γ-CD-F-COP, it was found that γ-CD-F-COF exhibited the highest benzaldehyde yield, approximately 82%, and maintained high catalytic efficiency even after multiple cycles. Figure 11 Figure c demonstrates its excellent catalytic performance. Compared with the crystalline γ-CD-F-COF prepared by the pre-assembly strategy of this invention, this control sample exhibits a significantly lower benzaldehyde yield in the catalytic oxidation of cinnamaldehyde, which directly proves the key role of the material's ordered structure and well-developed pores in improving catalytic performance.

[0065] Existing cyclodextrin COFs (such as those linked by borate ester bonds) rely on reversible covalent bonds to achieve high crystallinity, resulting in poor chemical stability, especially easy hydrolysis in aqueous phases, which limits their practical applications. While cyclodextrin polymers have relatively good stability, their disordered structure limits their performance. The technical solution in this application innovatively adopts a "pre-assembly-post-crosslinking" strategy. First, a thermodynamically stable ordered precursor is constructed through supramolecular interactions or coordination bonds, solving the "orderliness" problem; then, an irreversible aromatic nucleophilic substitution reaction is used to form ether bonds, solving the "stability" problem.

[0066] The internal cavities of cyclodextrin polymers are often blocked, resulting in high substrate mass transfer resistance and inability to reach the substrate, leading to low catalytic efficiency. In the technical solution of this application, the ordered precursor framework not only maintains the regular arrangement of cyclodextrins, but its well-developed pores also efficiently enrich hydrophobic crosslinking agent fluorobenzene monomers before the crosslinking reaction. This enrichment ability is also applicable to hydrophobic substrates (such as cinnamaldehyde) in the catalytic process. The formed γ-CD-F-COF has regular, open pores (approximately 1.7 nm), reducing the diffusion resistance of substrates and products. The cyclodextrin cavities are highly exposed and orderly arranged, with accessibility far exceeding that of cyclodextrin polymers. Experiments show that γ-CD-F-COF has a higher enrichment capacity for cinnamaldehyde than γ-CD itself and the amorphous control (γ-CD-F-COP). This enrichment effect synergizes with the molecular recognition ability of the cyclodextrin cavities, achieving an 82% yield in the cinnamaldehyde oxidation reaction, significantly better than the control sample.

[0067] Traditional COF synthesis often requires strict anhydrous and oxygen-free conditions, high temperature and pressure, and tube sealing, making it difficult to scale up. The technical solution in this application features a mild pre-assembly step, and the critical ether bond formation reaction does not require a strictly inert atmosphere or high pressure. This method successfully achieves gram-scale preparation at atmospheric pressure. This method simplifies the operation process, reduces equipment and energy consumption requirements, and demonstrates good potential for process scale-up and industrialization.

[0068] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A method for preparing a cyclodextrin covalent organic framework material, characterized in that: The method steps include: (1) Dissolve γ-cyclodextrin in the first organic solvent and mix well to obtain a homogeneous solution. Heat the solution to prepare γ-CD crystals. Alternatively, γ-cyclodextrin and a strong base are dissolved in deionized water, the aqueous solution is filtered, and the vapor of the first organic solvent is diffused into the solution. After 3 to 7 days, colorless and transparent crystals are generated. After the reaction is completed, the crystals are centrifuged, washed, and dried under vacuum to obtain γ-CD-MOF. (2) Add catalyst, fluorobenzene monomer and second organic solvent to γ-CD crystal or γ-CD-MOF, heat at above 80°C for more than 4 days, centrifuge and wash after the reaction, and then vacuum dry to obtain cyclodextrin covalent organic framework material.

2. The method for preparing a cyclodextrin covalent organic framework material as described in claim 1, characterized in that: In step (1), the first organic solvent includes N,N-dimethylformamide or methanol.

3. The method for preparing a cyclodextrin covalent organic framework material as described in claim 1, characterized in that: In step (1), the reaction is heated at 85~100℃ for more than 30 hours.

4. A method for preparing a cyclodextrin covalent organic framework material as described in any one of claims 1 to 3, characterized in that: In step (1), the strong base is potassium hydroxide; the molar ratio of γ-CD to potassium hydroxide is 1:

8.

5. The method for preparing a cyclodextrin covalent organic framework material as described in claim 1, characterized in that: In step (2), the catalyst is potassium carbonate; the fluorobenzene monomer includes tetrafluoroterephthalonitrile, decafluorobiphenyl, 2,6-difluoroterephthalonitrile, 2,5-difluoroterephthalonitrile, and 2,3-difluoroterephthalonitrile; the second organic solvent includes mesitylene and N,N-dimethylformamide.

6. A method for preparing a cyclodextrin covalent organic framework material as described in claim 1 or 5, characterized in that: In step (2), the molar ratio of the γ-CD crystal or γ-CD-MOF, catalyst, and fluorobenzene monomer is 1:8~16:2.

27.

7. The method for preparing a cyclodextrin covalent organic framework material as described in claim 1, characterized in that: In step (2), the reaction is heated at 85~100℃ for 4~5 days.

8. The method for preparing a cyclodextrin covalent organic framework material as described in claim 1, characterized in that: In steps (1) and (2), the washing process involves rinsing with water, N,N-dimethylformamide and tetrahydrofuran (THF) in sequence.

9. A cyclodextrin covalent organic framework material, characterized in that: It is prepared by the method described in any one of claims 1 to 8.

10. The application of the cyclodextrin covalent organic framework material according to claim 9, characterized in that: The material is used as a heterogeneous catalyst in host-guest interaction-driven catalytic reactions.

Images