Ion cage connected covalent organic framework compound and preparation method and application thereof

Abstract

The application discloses an ion cage connected covalent organic framework compound and a preparation method and application thereof. The preparation method comprises the following steps: mixing an iron source, an oxime base derivative, a boric acid base derivative, a first solvent and a second solvent, and performing a liquid nitrogen freezing-pump air extraction-freezing cycle degassing treatment, then sealing and performing a condensation reaction to prepare a metal chelate connected covalent organic framework compound; and performing acid treatment on the metal chelate connected covalent organic framework compound to prepare the ion cage connected covalent organic framework compound. The preparation method provided by the application has the advantages of easy raw material, mild conditions, simple operation, and the like, and the prepared covalent organic framework compound has a clear cavity structure and a periodic arrangement of coordination sites, exhibits excellent chemical stability and regular channel characteristics, and has a wide application prospect in the fields of ion adsorption separation, heterogeneous catalysis and the like.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, specifically relating to an ion-cage-linked covalent organic framework compound, its preparation method, and its application. Background Technology

[0002] Covalent organic frameworks (COFs), with their customizable crystal structures and well-defined nanopores, provide an ideal platform for developing highly efficient ion adsorption and separation materials. Studies have shown that by precisely controlling the pore size and pore wall chemical environment of COFs, efficient sieving and selective capture of specific ions can be achieved. For example, in COF membrane separation systems, the separation performance depends not only on the precise pore size confinement effect but also on the electrostatic interactions between ions and acidic functional groups such as sulfonic acid and carboxyl groups modified on the pore walls, or the specific coordination of ions with neutral functional groups such as ether chains. However, traditional functionalization strategies are often limited to single chemical modifications of the pores, making it difficult to construct an ideal adsorption structure with both high-density active sites and precise three-dimensional spatial arrangement while maintaining the integrity of the framework structure. This severely limits the adsorption capacity and selective separation efficiency of the materials for target ions.

[0003] Achieving precise synchronous construction of functional structures and the COF framework is a key challenge. Ideal ion-adsorption structures require functional units to form a defined spatial configuration and orientation within the pores. However, this process faces intrinsic kinetic competition with the dynamic covalent crystallization process of COFs: premature coordination of functional groups or steric hindrance significantly interferes with the reversible formation and defect repair of dynamic covalent bonds such as imine bonds, leading to decreased framework crystallinity; conversely, excessively rapid crystallization rates hinder the ordered assembly of functional units. Existing studies generally employ post-modification or stepwise synthesis strategies to introduce adsorption sites, which are not only cumbersome but also difficult to achieve a uniform and periodic distribution of functional sites within the framework. Therefore, developing new methods that can synergistically promote covalent assembly and the directional generation of functional structures is crucial for advancing this field. Summary of the Invention

[0004] The main objective of this invention is to provide an ion-cage-linked covalent organic framework compound, its preparation method, and its application, in order to overcome the shortcomings of the prior art.

[0005] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0006] This invention provides a method for preparing ion-cage-linked covalent organic framework compounds, comprising:

[0007] Iron source, oxime derivative, borate derivative, first solvent and second solvent are mixed and degassed by liquid nitrogen freezing-pump evacuation-thawing cycle, and then sealed for condensation reaction to obtain metal chelate linked covalent organic framework compound.

[0008] Furthermore, the covalent organic framework compound linked by the metal chelate is subjected to acid treatment to obtain an ion-cage linked covalent organic framework compound.

[0009] This invention also provides ion-cage-linked covalent organic framework compounds prepared by the aforementioned method, wherein the ion-cage-linked covalent organic framework compounds have repeating structural units as shown in formula (III):

[0010] ,

[0011] Formula (III);

[0012] Where X is selected from C or Si.

[0013] The embodiments of the present invention also provide the application of the aforementioned ion cage-linked covalent organic framework compounds in the fields of ion adsorption separation or heterogeneous catalysis.

[0014] Compared with existing technologies, the advantages of this invention are as follows: This invention employs a one-step hydrothermal method to directly construct a structurally stable metal chelate-linked covalent organic framework through the synergistic effect of dynamic covalent and coordination bonds. Then, metal ions are removed sequentially using acid / alkali solutions to form a covalent organic framework compound linked by ion cages. In this material, by removing metal ions from the FeN6 coordination centers, stable, periodically distributed, and well-sized sub-nanometer cavities are obtained within the COF framework. This technical solution not only maintains the permeability and transport capacity of porous materials but also achieves efficient recognition and stable capture of target ions through precise chemical microenvironment design within the cavities. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the synthesis route in Embodiment 1 of the present invention;

[0017] Figure 2 This is the powder X-ray diffraction pattern of Fe-COF-1, the intermediate product synthesized in Example 1 of this invention;

[0018] Figure 3 These are the infrared spectra of the monomers and intermediate product Fe-COF-1 required for synthesis in Example 1 of this invention;

[0019] Figure 4 These are the solid-state boron NMR spectra of the monomer TPBM and the intermediate product Fe-COF-1 required for synthesis in Example 1 of this invention;

[0020] Figure 5 This is the solid-state carbon NMR spectrum of Fe-COF-1, the intermediate product synthesized in Example 1 of this invention;

[0021] Figure 6 This is the X-ray photoelectron spectrum of the intermediate product Fe-COF-1 in Example 1 of this invention;

[0022] Figure 7 This is a transmission electron microscope image of the intermediate product Fe-COF-1 in Example 1 of the present invention;

[0023] Figure 8 This is a nitrogen adsorption-desorption curve of the intermediate product Fe-COF-1 in Example 1 of the present invention;

[0024] Figure 9 This is a pore size distribution diagram of the intermediate product Fe-COF-1 in Example 1 of the present invention;

[0025] Figure 10 This is the powder X-ray diffraction pattern of the product ion cage-linked covalent organic framework compound (COF-1) in Example 1 of this invention;

[0026] Figure 11 This is the infrared spectrum of product COF-1 in Example 1 of the present invention. Detailed Implementation

[0027] In view of the deficiencies of existing technologies, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. This invention innovatively proposes the design concept of constructing a periodic "ion cage" structure within a covalent organic framework (COF), successfully preparing an ion-cage-connected COF material. This material possesses precisely sized, chemically controllable sub-nanometer cavities. While maintaining the inherent ion permeation and transport properties of the porous framework, it achieves efficient and stable capture of target ions under low-concentration conditions by utilizing the regularly arranged cavities formed after removing metals at metal-nitrogen (MN6) sites. This "ion cage" structure effectively solves the problems of disordered adsorption site distribution and uneven binding strength in traditional functionalized COFs, providing a novel design concept and technical path for developing next-generation high-performance ion adsorption and separation materials. The technical solution of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0028] The purpose of this invention is to innovatively propose a design concept for constructing a periodic "ion cage" structure within a covalent organic framework (COF), and successfully prepare an ion-cage-connected COF material. This material possesses precisely sized, chemically controllable sub-nanometer cavities. While maintaining the inherent ion permeation and transport properties of the porous framework, it achieves efficient and stable capture of target ions under low-concentration conditions by utilizing the regularly arranged cavities formed after removing the metal at metal-nitrogen (MN6) sites. This "ion cage" structure effectively solves the problems of disordered adsorption site distribution and uneven binding strength in traditional functionalized COFs, providing a novel design concept and technical path for developing next-generation high-performance ion adsorption and separation materials.

[0029] Specifically, as one aspect of the technical solution of this invention, a method for preparing an ion-cage-linked covalent organic framework compound includes:

[0030] Iron source, oxime derivative, borate derivative, first solvent and second solvent are mixed and degassed by liquid nitrogen freezing-pump evacuation-thawing cycle, and then sealed for condensation reaction to obtain metal chelate linked covalent organic framework compound.

[0031] Furthermore, the covalent organic framework compound linked by the metal chelate is subjected to acid treatment to obtain an ion-cage linked covalent organic framework compound.

[0032] This invention uses ferrous ions from different iron sources as templates to coordinate with oxime derivatives to form metal chelates, and then with T... d- Symmetrical boric acid derivatives are covalently linked to expand the three-dimensional topological network structure of the metal chelate linkage; then, metal ions are removed by acid / alkali solutions to form a covalent organic framework compound linked by ion cages.

[0033] In some preferred embodiments, the iron source includes a ferrous ion iron source, which includes FeCl2 and / or FeSO4, but is not limited thereto.

[0034] In some preferred embodiments, the borate derivative has a structure as shown in formula (I):

[0035] ,

[0036] Formula (I),

[0037] Where X is selected from C or Si.

[0038] In some preferred embodiments, the oxime derivative has a structure as shown in formula (II):

[0039] ,

[0040] Equation (II).

[0041] In some preferred embodiments, the first solvent includes any one or more combinations of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, and tert-butanol, and is not limited thereto.

[0042] In some preferred embodiments, the second solvent includes acetone, but is not limited thereto.

[0043] In some preferred embodiments, the molar ratio of the borate derivative, oxime derivative and iron source is 1:(5~7):(1.8~2.5).

[0044] In some preferred embodiments, the volume ratio of the first solvent to the second solvent is 1:(0.05~0.4).

[0045] In some preferred embodiments, the condensation reaction is carried out at a temperature of 60–100°C for a time of 70–170 h.

[0046] In some preferred embodiments, the metal chelate-linked covalent organic framework compound has a doubly interpenetrating dia topology.

[0047] In some preferred embodiments, the metal-chelate-linked covalent organic framework compound has a double interpenetrating dia topology, belonging to space group P-4B2, with cell parameters: a = b = 26.29 Å, c = 24.10 Å, α = β = γ = 90°. o .

[0048] In some preferred embodiments, the acid treatment is used to selectively remove iron ions from FeN6 coordination centers, forming regular cavity structures with a size of 1.9-2.6 Å in the framework.

[0049] In some preferred embodiments, the preparation method specifically includes:

[0050] S1. Add the iron source, oxime derivative, borate derivative, first solvent and second solvent to the reaction apparatus and mix them. Then, after three cycles of liquid nitrogen freezing-pump evacuation-thawing to degas the mixture, seal the reaction apparatus and carry out the condensation reaction.

[0051] S2. After the condensation reaction is completed, cool to room temperature, filter to collect the solid, and wash the obtained solid with an organic solvent;

[0052] S3. The solid obtained in step S2 was purified by Soxhlet extraction and then dried to obtain a metal chelate-linked covalent organic framework compound.

[0053] S4. The covalent organic framework compound linked by the metal chelate is soaked in acid and washed with deionized water.

[0054] S5. The solid obtained in step S4 is soaked in alkaline solution and washed with deionized water, and then dried to obtain a covalent organic framework compound with ion cages.

[0055] Furthermore, the acid solution includes, but is not limited to, hydrochloric acid.

[0056] Furthermore, the concentration of the acid solution is 0.5~5 mol / L.

[0057] Furthermore, the alkaline solution includes, but is not limited to, a sodium hydroxide solution.

[0058] Furthermore, the concentration of the alkaline solution is 0.5~5 mol / L.

[0059] In some preferred embodiments, the method for preparing the ion-cage-linked covalent organic framework compound includes:

[0060] (1) Raw material preparation

[0061] Function: Precise control of raw material ratio.

[0062] Implementation scheme: A three-component precise metering system is adopted, in which the borate derivative is selected from T d - The symmetrical boric acid derivative and oxime derivative used were 1,2-cyclohexanedione dioxime, and the iron source was anhydrous ferrous chloride. The molar ratio of the three was strictly controlled at 1:6:2. This ratio was based on the following technical considerations: the excess oxime derivative ensured sufficient coordination with the iron source to form a FeN6 structure, while also guaranteeing effective condensation with the boric acid derivative. The weighing accuracy of the raw materials was controlled within ±0.1 mg, and the weighing operation was performed using an analytical balance in a dry environment.

[0063] (2) Raw material pretreatment

[0064] Function: Deoxygenation treatment of the reaction system.

[0065] Implementation plan: A three-step freezing-degassing cycle process is adopted. First, the mixture is rapidly frozen to -196°C in liquid nitrogen, and then the vacuum pump is started to reduce the system pressure to 10. -3 Pa, maintain for 5 minutes, then slowly heat to room temperature to thaw. Repeat this cycle three times to ensure complete removal of dissolved oxygen. The technical principle lies in fixing the reaction solution by freezing and allowing dissolved gases to escape under vacuum conditions, thereby creating an oxygen-free reaction environment.

[0066] (3) Condensation reaction and structural assembly

[0067] Function: The ion cage and framework structure are constructed simultaneously.

[0068] Implementation scheme: A single-stage temperature control strategy of 70±2℃ is adopted. This temperature condition has been optimized and screened to effectively achieve the condensation reaction of boric acid and oxime groups to form the primary structure of the COF framework, while simultaneously promoting Fe... 2+ The FeN6 ion cage structure is constructed through coordination with the oxime nitrogen atom. The reaction is carried out in a sealed, heat-resistant glass tube, and the reaction system remains stable under autogenous pressure for 70–170 hours.

[0069] Technical principle explanation: The co-assembly process under this temperature condition is based on the following mechanism: Under thermodynamic conditions of 70℃, the condensation reaction rate of boric acid with oxime is related to Fe... 2+ The coordination rate reaches an optimal matching state. While forming a boronic acid ester bond, the nitrogen atom in the oxime group has its lone pair electrons interacting with Fe. 2+ Coordination occurs, forming a stable six-coordinate structure. This single-temperature strategy avoids structural rearrangement and defects that may occur during multi-stage heating, ensuring the synchronous and uniform construction of the ion cage structure and the COF framework.

[0070] (4) Deep purification

[0071] Function: Highly efficient impurity removal and pore purification.

[0072] Implementation Scheme: An improved Soxhlet extraction and purification system was employed, establishing a sequential solvent washing process. First, methanol was used as the extraction solvent, continuously extracted at 90°C for 12 hours to effectively remove polar impurities and unreacted monomers. Subsequently, acetone was switched to the solvent, and extraction continued at 87°C for 12 hours to remove moderately polar and non-polar impurities. Solvent switching was achieved through a specially designed dual solvent exchange system, ensuring a smooth transition and preventing the collapse of the sample's porous framework structure.

[0073] Technical principle explanation: This sequential solvent washing strategy is based on precise matching of solubility parameters. Methanol (δ) p =12.3MPa¹ / ²) It can effectively dissolve polar oxime derivatives and metal salt byproducts, while acetone (δ) p = 10.4 MPa¹ / ²) exhibits excellent solubility for boric acid derivatives and intermediates. This sequential extraction method achieves the fractional removal of various impurities while maintaining the structural integrity of the COF framework.

[0074] (5) Activation

[0075] Function: Acid treatment activation and selective purification.

[0076] Implementation: The product was soaked in 1M hydrochloric acid solution at room temperature for 24 hours, with a solid-liquid ratio controlled at 1:150. This concentration condition was systematically optimized to effectively remove unstable iron species and surface-adsorbed impurity ions while maintaining the integrity of the FeN6 core structure. After acid treatment, the solid was collected by centrifugation and washed with deionized water until the conductivity of the washing solution was below 5 μS / cm to ensure no free ions remained.

[0077] Technical principle explanation: 1M hydrochloric acid selectively removes iron ions from FeN6, constructing a precise cavity of 1.9-2.6 Å within the COF framework. This "ion cage" structure combines size sieving and coordination recognition functions. The six nitrogen atoms enriched on the cavity surface provide an ideal coordination microenvironment for subsequent target ion recognition, realizing a functional transformation from a "metal coordination center" to an "ion recognition cavity."

[0078] (6) Performance optimization

[0079] Function: Alkali treatment and selective regeneration.

[0080] Implementation scheme: Treatment with 1M potassium hydroxide solution at room temperature for 12 hours aims to neutralize the protons at the nitrogen sites in the ion cage. Simultaneously, taking advantage of the large ionic radius of potassium ions (1.38 Å), which prevents them from entering the ion cage to form a stable cavity, the ion cage structure remains vacant and usable. After alkali treatment, the solution is washed with deionized water until neutral and dried under vacuum at 60°C for 24 hours.

[0081] Technical principle explanation:

[0082] The use of potassium hydroxide serves a dual purpose: first, to neutralize surface protons generated during acid treatment and restore the chemical equilibrium of the material; second, to prevent potassium ions from entering the coordination cavity of the ion cage due to size effects, thus avoiding competitive coordination and ensuring the ion cage's exclusive recognition capability for the target ion. This characteristic is based on the precise size design of the FeN6 ion cage, whose cavity size (1.9-2.6 Å) and geometry precisely exclude the possibility of stable coordination of potassium ions.

[0083] The technical solution of the present invention solves the following problems: (1) It completely solves the problem of disordered spatial distribution of functional sites: the active sites of functionalized COF materials prepared by traditional methods are randomly distributed, resulting in significant differences in the geometric configuration and binding ability of different sites. The present invention ensures that all active sites have completely consistent spatial configuration and electronic structure through the periodic arrangement of ion cages, and realizes uniform and predictable binding characteristics to target ions; (2) It breaks through the efficiency bottleneck of post-modification strategy: the heterogeneous post-modification process relied upon by the existing technology has serious mass transfer limitations, resulting in insufficient modification of internal sites and easy destruction of the integrity of the framework structure. The in-situ assembly strategy of the present invention avoids the subsequent modification steps, realizes high-density and fully uniform introduction of functional sites, and perfectly maintains the long-range order of the crystal framework; (3) It significantly improves the ion trapping ability under low concentration conditions. Energy: Traditional materials rely on a single action mechanism, and their performance drops sharply under complex systems or low concentration conditions. The three-level synergistic mechanism of “size sieving-pre-enrichment-strong coordination” created by this invention enables the material to maintain excellent capture efficiency and selectivity even at extremely low concentrations; (4) Ensures the reproducibility and stability of material performance: By integrating the ion cage as a clear secondary structural unit into the design system, this invention achieves the thermodynamic stability and kinetic controllability of the functional structure, solves the common industry problem of large batch differences and unstable performance of materials prepared by traditional methods, and provides a reliable guarantee for the practical application of materials.

[0084] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0085] (1) Existing technologies typically employ a multi-stage temperature control strategy, first completing the initial formation of the COF framework at a lower temperature (approximately 85°C), and then raising the temperature to a higher temperature (approximately 105°C) to promote metal coordination. While this method can optimize the two reaction steps separately, it has several inherent drawbacks: thermal stress during temperature changes can easily lead to crystal defects; structural reorganization during phase transitions may destroy the already formed coordination bonds; and multi-stage control increases process complexity and equipment requirements. In contrast, the single-stage isothermal synthesis strategy adopted in this invention achieves an ideal match between the condensation reaction and the coordination process through precise control of reaction kinetics. This innovation brings multiple advantages: First, isothermal conditions eliminate structural stress caused by temperature fluctuations, resulting in more uniform and complete crystal growth; second, it simplifies equipment requirements and control logic, allowing the reaction to be completed in ordinary heat-resistant glass tubes, avoiding the equipment and safety requirements of traditional high-pressure reactors; third, the appropriate extension of the reaction time (70-170 hours) ensures the full conversion of reactants under mild conditions, avoiding side reactions and structural degradation that may occur at high temperatures.

[0086] (2) Precise Proportioning Design and Improved Reaction Efficiency: In existing technologies, the proportions of functional monomers are often determined based on experience, lacking a systematic stoichiometric basis, leading to low reaction efficiency and resource waste. A common practice is to use equimolar ratios or a slight excess of metal sources, which easily produces uncoordinated metal clusters or heterogeneous precipitation, affecting the uniformity of material properties. This invention, based on coordination chemistry principles, innovatively employs a precise molar ratio (boronic acid derivative: oxime derivative: iron source). The scientific basis for this design is that an appropriate amount of oxime derivative ensures that each Fe... 2+ All ions can obtain a sufficient coordination environment to form a complete FeN6 structure; at the same time, an appropriate amount of oxime groups can also participate in framework construction, avoiding framework defects caused by coordination competition. Practical results show that this ratio significantly improves the batch-to-batch consistency of ion cage-connected COFs.

[0087] (3) Selective acid-base activation treatment: Traditional methods often employ extreme conditions for material activation, such as high-concentration acids (above 3M) or long-term treatment with strong bases. While these conditions can effectively activate materials, they can easily lead to structural damage and destruction of functional sites. The 1M hydrochloric acid-1M potassium hydroxide sequential treatment scheme of this invention embodies the concept of "precise activation." The 1M hydrochloric acid concentration has been carefully optimized to remove unstable metal species while maintaining the integrity of the B−O−N linkage structure. Particularly noteworthy is the innovative use of potassium hydroxide: utilizing the characteristic that the large ionic radius of K⁺ (1.38Å) prevents the formation of stable coordination within the FeN6 cavity (approximately 1.0 nm), it achieves both proton neutralization and avoids the occupation of active sites by competing ions. This design ensures the vacancy and availability of the ion cage structure, providing ideal conditions for subsequent target ion capture.

[0088] (4) Comprehensive benefits of mild processing conditions: Compared with traditional methods, the activation process of the present invention is carried out at room temperature, avoiding the skeleton collapse and functional group degradation that may be caused by high-temperature processing. Actual tests show that the optimized activation process significantly improves the recyclability of the material.

[0089] (5) Unity of structural integrity and functionality: COF materials prepared by existing technologies often struggle to balance structural integrity and functionality: pursuing high crystallinity may lead to insufficient functional site density, while increasing functional site density may affect structural order. This invention successfully solves this contradiction through a collaborative assembly strategy, achieving high functional site density while maintaining high crystallinity.

[0090] (6) Significantly improved adsorption performance: In terms of key performance indicators, the material of this invention exhibits significant advantages: it achieves specific extraction of low-concentration target ions (Li or Na) from mixed solutions (Li-K, Na-K) with an extraction rate of over 30 wt%; and the removal rate of transition metal ions under low-concentration conditions (~50 ppm) reaches over 99.9%. These performance improvements are directly attributable to the precise control of the material structure and the optimized design of the active sites.

[0091] Another aspect of the present invention provides an ion-cage-linked covalent organic framework compound prepared by the aforementioned method, wherein the ion-cage-linked covalent organic framework compound has repeating structural units as shown in formula (III):

[0092] ,

[0093] Formula (III);

[0094] Where X is selected from C or Si.

[0095] Furthermore, the covalent organic framework compound is a crystalline porous compound.

[0096] Furthermore, the ion-cage-connected covalent organic framework compound has a doubly interpenetrating dia topology.

[0097] Another aspect of the present invention provides the application of the aforementioned ion-cage-linked covalent organic framework compounds in the fields of ion adsorption separation or heterogeneous catalysis.

[0098] Furthermore, the application includes the use of the ion-cage-connected covalent organic framework compounds in Li / K or Li / Na separation and adsorption separation.

[0099] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0100] Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0101] Example 1: Ion cage-linked covalent organic framework compound (COF-1) for Li / K separation

[0102] (1) Preparation of ion-cage linked covalent organic framework compounds (COF-1) Figure 1 (Schematic diagram of the synthetic route): 1,2-cyclohexanedione dioxime (NX, 17.1 mg), anhydrous ferrous chloride (FeCl2, 5.1 mg), and tetra(4-boratephenyl)methane (TPBM, 9.9 mg) were placed in a heat-resistant glass tube, and a mixed solution of ethanol and acetone at a volume ratio of 1:0.15 (1.15 mL) was added. The mixture was sonicated to ensure homogeneity. Then, three cycles of liquid nitrogen freezing-pump evacuation-thawing were rapidly performed, followed by flame sealing of the glass tube under vacuum. The glass tube was placed in a 70°C oven for 120 h to obtain a brown precipitate. After the reaction was completed, the mixture was cooled to room temperature, and the solid was separated by filtration. The obtained solid product was then washed with methanol (40 mL) and acetone (40 mL) for 24 h by Soxhlet extraction. Finally, the solid product was vacuum dried to obtain Fe-COF-1 (17.7 mg, yield 67.4%).

[0103] The product was then soaked in 1 M HCl and 1 M KOH for 24 h each, and washed multiple times with deionized water (3 × 40 mL) to remove acid and alkali residues. After drying, the product COF-1 was obtained.

[0104] (2) COF-1 for Li / K separation: 20 mg COF-1 was soaked in a mixed solution of lithium chloride / potassium chloride (n / n = 1:1) (where the lithium ion concentration was 8.0 ppm) for 12 h. The concentration of lithium ions before and after adsorption was obtained by ICP-MAS test, and the adsorption efficiency of lithium ions was calculated to be 38.4±6.2wt%.

[0105] (3) Product characterization:

[0106] Figure 2 The powder X-ray diffraction pattern of the synthetic intermediate Fe-COF-1 is shown. The pattern shows peaks at 5.7, 7.35, 9.4, 11.75, and 18.6°, confirming that a novel three-dimensional covalent organic framework compound was successfully synthesized by the method of this invention.

[0107] Figure 3 The infrared spectra of the monomers required for synthesis and the intermediate Fe-COF-1 are shown. The infrared spectra reveal the synthesized three-dimensional covalent organic framework compound at 1610 cm⁻¹. -1 1348 cm -1 and 964 cm -1 The presence of characteristic absorption peaks, attributed to the presence of C=N, B−O, and N−O bonds, indicates the successful synthesis of the compound.

[0108] Figure 4 Solid-state NMR boron spectra of the monomer TPBM and the intermediate product Fe-COF-1 are shown, indicating that the monomer TPBM is transformed from triangular planar boron sites to tetrahedral boron sites in the product Fe-COF-1.

[0109] Figure 5 The solid-state carbon NMR spectrum of the synthetic intermediate Fe-COF-1 is shown. The presence of diffraction peaks for each carbon in the spectrum indicates the synthesis of the compound. At the same time, the sharp and independent peak shapes also indicate that the polymer has good crystallinity.

[0110] Figure 6 The X-ray photoelectron spectrum of the intermediate product Fe-COF-1 is shown, indicating that the material is composed of C, N, O, B and Fe, with iron mostly existing in the divalent form.

[0111] Figure 7 Transmission electron microscopy (TEM) images of the intermediate Fe-COF-1 are shown, revealing distinct alternating light and dark lattice fringes, further confirming that the compound is a crystalline polymer.

[0112] Figure 8 The nitrogen adsorption-desorption curves of the intermediate Fe-COF-1 are shown, with a BET specific surface area of ​​455.5 m².2 g -1 .

[0113] Figure 9 The pore size distribution of the intermediate product Fe-COF-1 is shown, with pore sizes of 0.5 nm and 1.27 nm.

[0114] Figure 10 The powder X-ray diffraction pattern of the product ion cage-linked covalent organic framework compound (COF-1) is shown, indicating that the product maintained good crystallinity after ion removal.

[0115] Figure 11 The infrared spectrum of product COF-1 is shown at 1610 cm⁻¹. -1 1348 cm -1 and 964 cm -1 The presence of characteristic absorption peaks indicates that the product maintains the original covalent bonds in its backbone.

[0116] Example 2: Ion cage-linked covalent organic framework compound (COF-2) for Li / K separation

[0117] Preparation of ion-cage-linked covalent organic framework compound (COF-2): 1,2-cyclohexanedione dioxime (NX, 17.1 mg), anhydrous ferrous chloride (FeCl2, 5.1 mg), and (silanetetramethyltetra(phenyl-4,1-diyl))tetraboronic acid (TPBS, 10.2 mg) were placed in a heat-resistant glass tube. A mixture of ethanol and acetone (1:0.15, v / v) (1.15 mL) was added, and the mixture was sonicated to ensure homogeneity. The mixture was then subjected to three rapid cycles of liquid nitrogen freezing-pump evacuation-thawing, followed by flame sealing under vacuum. The glass tube was then placed in a 70°C oven for 120 h to obtain a brown precipitate. After the reaction was complete, the mixture was cooled to room temperature, and the solid was separated by filtration. The obtained solid product was then washed with methanol (40 mL) and acetone (40 mL) for 24 h by Soxhlet extraction. Finally, the solid product was vacuum dried to obtain COF-2 (20.4 mg, yield 69.8%).

[0118] The product was then soaked in 1 M HCl and 1 M KOH for 24 h each, and washed multiple times with deionized water (3 × 40 mL) to remove acid and alkali residues. After drying, the product COF-2 was obtained.

[0119] COF-2 was used for Li / K separation: 20 mg of COF-2 was soaked in a mixed solution of lithium chloride / potassium chloride (n / n = 1:1) (where the lithium ion concentration was 8.0 ppm) for 12 h. The concentration of lithium ions before and after adsorption was measured by ICP-MAS, and the adsorption efficiency of lithium ions was calculated to be 35.2 ± 6.8 wt%.

[0120] Example 3: Ion cage-linked covalent organic framework compound (COF-1) for Na / K separation

[0121] Preparation of ion-cage linked covalent organic framework compound (COF-1): 1,2-cyclohexanedione dioxime (NX, 17.1 mg), anhydrous ferrous chloride (FeCl2, 5.1 mg), and tetrakis(4-boratephenyl)methane (TPBM, 9.9 mg) were placed in a heat-resistant glass tube. A mixed solution of ethanol and acetone (1.15 mL, v / v) was added, and the mixture was sonicated to ensure homogeneity. The mixture was then subjected to three rapid cycles of liquid nitrogen freezing-pump evacuation-thawing, followed by flame sealing of the glass tube under vacuum. The glass tube was then placed in a 70°C oven for 120 h to obtain a brown precipitate. After the reaction was complete, the mixture was cooled to room temperature, and the solid was separated by filtration. The obtained solid product was then washed with methanol (40 mL) and acetone (40 mL) for 24 h by Soxhlet extraction. Finally, the solid product was vacuum dried to obtain Fe-COF-1 (17.7 mg, yield 67.4%).

[0122] The product was then soaked in 1 M HCl and 1 M KOH for 24 h each, and washed multiple times with deionized water (3 × 40 mL) to remove acid and alkali residues. After drying, the product COF-1 was obtained.

[0123] COF-1 was used for Na / K separation: 20 mg of COF-1 was soaked in a sodium chloride / potassium chloride (n / n = 1:1) mixed solution (where the sodium ion concentration was 8.0 ppm) for 12 h, and the sodium ion concentration was obtained by ICP-MAS test. The adsorption efficiency of sodium ions was calculated to be 37.5 ± 5.6 wt%.

[0124] Example 4: Ion cage-linked covalent organic framework compound (COF-1) for low concentration transition metal ions (M 2+ M 2+ = Fe 2+ Co 2+ Ni 2+ Cu 2+ Zn 2+ Adsorption

[0125] Preparation of ion-cage linked covalent organic framework compound (COF-1): 1,2-cyclohexanedione dioxime (NX, 17.1 mg), anhydrous ferrous chloride (FeCl2, 5.1 mg), and tetra(4-boratephenyl)methane (TPBM, 9.9 mg) were placed in a heat-resistant glass tube, and a mixed solution of ethanol and acetone at a volume ratio of 1:0.15 (1.15 mL) was added. The mixture was sonicated to ensure homogeneity. Then, three rapid cycles of liquid nitrogen freezing-pump evacuation-thawing were performed, followed by flame sealing of the glass tube under vacuum. The glass tube was placed in a 70 °C oven for 120 h to obtain a brown precipitate. After the reaction was complete, the mixture was cooled to room temperature, and the solid was separated by filtration. The obtained solid product was then washed with methanol (40 mL) and acetone (40 mL) for 24 h by Soxhlet extraction. Finally, the solid product was vacuum dried to obtain Fe-COF-1 (17.7 mg, yield 67.4%).

[0126] The product COF-1 was obtained by soaking in 1 M HCl and 1 M KOH for 24 h each, and washing with deionized water (3 × 40 mL) several times during the soaking period to remove acid and alkali residues. After drying, the product COF-1 was obtained.

[0127] COF-1 is used for low concentrations of transition metal ions (M 2+ M 2+ = Fe 2+ Co 2+ Ni 2+ Cu 2+ Zn 2+ Adsorption: 20 mg COF-1 was soaked in a mixed solution of ferric chloride / cobalt chloride / nickel chloride / copper chloride / zinc chloride (n / n / n / n / n = 1:1:1:1:1) (where the iron ion concentration was 50.0 ppm) for 12 h. The concentrations of each transition metal ion before and after adsorption were measured by ICP-MAS, and the adsorption efficiency was calculated to be above 99.9%.

[0128] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0129] It should be understood that the technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made to the technical solutions of the present invention without departing from the spirit and scope of the claims are within the scope of protection of the present invention.

Claims

1. A method for preparing an ion-cage-linked covalent organic framework compound, characterized in that, include: Iron source, oxime derivative, borate derivative, first solvent and second solvent are mixed and degassed by liquid nitrogen freezing-pump evacuation-thawing cycle, and then sealed for condensation reaction to obtain metal chelate linked covalent organic framework compound. Furthermore, the covalent organic framework compound linked by the metal chelate is subjected to acid treatment to obtain an ion-cage linked covalent organic framework compound.

2. The preparation method according to claim 1, characterized in that: The iron source includes a ferrous ion iron source, which includes FeCl2 and / or FeSO4. And / or, the borate derivative has a structure as shown in formula (I): ， Formula (I), Wherein, X is selected from C or Si; And / or, the oxime derivative has a structure as shown in formula (II): ， Formula (II); And / or, the first solvent includes any one or more combinations of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol and tert-butanol; And / or, the second solvent includes acetone.

3. The preparation method according to claim 1, characterized in that: The molar ratio of the borate derivative, oxime derivative and iron source is 1:(5~7):(1.8~2.5); And / or, the volume ratio of the first solvent to the second solvent is 1:(0.05~0.4).

4. The preparation method according to claim 1, characterized in that: The condensation reaction is carried out at a temperature of 60~100℃ for a time of 70~170 h.

5. The preparation method according to claim 1, characterized in that: The metal chelate-linked covalent organic framework compound has a double interpenetrating dia topology. And / or, the metal-chelate linked covalent organic framework compound has a doubly interpenetrating dia topology, belonging to space group P-4B2, with cell parameters: a = b = 26.29 Å, c = 24.10 Å, α = β = γ = 90°. o ; And / or, the acid treatment is used to selectively remove iron ions from FeN6 coordination centers, forming regular cavity structures with a size of 1.9-2.6 Å in the framework.

6. The preparation method according to claim 1, characterized in that, Specifically, it includes: S1. Add the iron source, oxime derivative, borate derivative, first solvent and second solvent to the reaction apparatus and mix them. Then, after three cycles of liquid nitrogen freezing-pump evacuation-thawing to degas the mixture, seal the reaction apparatus and carry out the condensation reaction. S2. After the condensation reaction is completed, cool to room temperature, filter to collect the solid, and wash the obtained solid with an organic solvent; S3. The solid obtained in step S2 was purified by Soxhlet extraction and then dried to obtain a metal chelate-linked covalent organic framework compound. S4. The covalent organic framework compound linked by the metal chelate is soaked in acid and washed with deionized water. S5. The solid obtained in step S4 is soaked in alkaline solution and washed with deionized water, and then dried to obtain a covalent organic framework compound with ion cages.

7. The preparation method according to claim 6, characterized in that: The acid solution includes hydrochloric acid; preferably, the concentration of the acid solution is 0.5~5 mol / L; And / or, the alkaline solution includes a sodium hydroxide solution; preferably, the concentration of the alkaline solution is 0.5~5 mol / L.

8. An ion-cage-linked covalent organic framework compound prepared by any one of the preparation methods of claims 1-7, characterized in that: The covalent organic framework compound connected by the ion cage has repeating structural units as shown in formula (III): ， Formula (III); Where X is selected from C or Si.

9. The ion-cage-linked covalent organic framework compound according to claim 8, characterized in that: The covalent organic framework compound is a crystalline porous compound.

10. The application of the ion-cage-linked covalent organic framework compound of claim 8 or 9 in the field of ion adsorption separation or heterogeneous catalysis; preferably, the application includes the application of the ion-cage-linked covalent organic framework compound in Li / K or Na / K separation adsorption separation.

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