A two-dimensional cofs material with large interlayer distance and preparation method and application thereof

Abstract

The application provides a kind of two-dimensional COFs material with large interlayer spacing and its preparation method and application, and relates to the technical field of thorium ion adsorption material.The material is prepared by the reaction of amino monomer and aldehyde group monomer containing crown ether.The crown ether is embedded into the COFs framework, effectively overcoming the challenge that flexible crown ether molecules may cause the crystallinity of the material to decrease, forming a two-dimensional network structure with stable structure and highly accessible adsorption sites, and showing a large interlayer spacing, which provides a good diffusion channel for the guest molecules, so that the hydrated thorium ions enter the interlayer and chemically chelate with the crown ether units in the sheet layer.More importantly, based on the dual coordination of crown ether units and imine bond to thorium ions, the material shows excellent adsorption capacity and selective recognition ability to thorium, and can separate, enrich and recover thorium ions in complex systems, and has wide application prospects in wastewater treatment, resource recovery and other fields.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of thorium ion adsorption materials, in particular to a two-dimensional COFs material with a large interlayer distance and a preparation method and application thereof. BACKGROUND

[0002] Nuclear energy, as an important alternative to fossil energy, has significant advantages in alleviating energy crisis and reducing carbon emissions, but the radioactive waste generated during its operation poses a serious threat to the ecological environment and human health. Improper handling of nuclear accidents and nuclear waste can lead to the entry of radionuclides into the environment, among which radionuclides with long half-lives and strong biological migration are particularly worth attention.

[0003] Thorium (Th) is a naturally radioactive element, and the main isotope is ²³²Th, with a half-life of 1.4 x 10 0 Th has potential application value in nuclear fuel cycle, and the transmutation of Th produces ²³³U which can be used as fissile fuel. Among the six types of reactors recommended by the International Forum on the Fourth Generation of Nuclear Energy Systems, thorium-based molten salt reactors are considered as one of the revolutionary technologies in the future of nuclear energy due to their inherent safety, excellent physical properties and potential fuel sustainability, and are attracting much attention. This development prospect has elevated the strategic position of thorium, which has not been used on a large scale for a long time, to an unprecedented height. However, thorium and its decay products (such as ²² 8 Ra, ²² 0 Rn) have alpha radiation toxicity, and if they enter the biological chain through water or soil, they can accumulate in the organism for a long time, causing internal radiation damage and increasing the risk of cancer. Therefore, developing efficient thorium ion adsorption and separation technology is not only an urgent need to address the challenges of radioactive pollution in the field of nuclear energy and to ensure environmental safety, but also a core support for promoting thorium-based nuclear energy, a future strategic industry, towards commercialization and achieving efficient recycling of resources.

[0004] Currently, thorium separation technologies include solvent extraction, ion exchange, and precipitation method, but traditional materials (such as inorganic zeolites and zirconium phosphate) rely on non-specific ion exchange, which has poor selectivity and low adsorption capacity in complex media. Covalent organic framework materials are crystalline porous materials formed by connecting light elements through strong covalent bonds. The design and synthesis of such materials have precise topological controllability, enabling periodic arrangement and precise control of pore structure at the molecular level, thereby having extremely high specific surface area, clear and adjustable pore size distribution, and surface modifiability. These characteristics make them have broad application potential in many fields such as chemical separation, heterogeneous catalysis, and sensing detection.

[0005] Crown ether is a kind of macrocyclic polyether with a specific size cavity, and its structure is composed of alternating ethylene units and oxygen atoms. Because the lone pair electrons of oxygen atoms are directed towards the inside of the cavity, it can selectively bind to metal cations of matching size to form stable host-guest complexes. This coordination ability shows a high degree of selectivity to the cation size, that is, the matching degree of the cavity diameter of the crown ether and the cation diameter directly determines the stability of the complex. In addition, the flexible structure of the crown ether macrocycle itself makes the molecular skeleton not rigidly arranged, but shows a certain dynamic adaptability. This dynamic adaptability promotes the formation of a large enough interlayer spacing between adjacent layers, thereby constructing an efficient and unobstructed diffusion channel for the rapid migration of these guest molecules between the layers. For this reason, crown ether has a wide range of applications in phase transfer catalysis, ion selective extraction, chemical sensors and supramolecular assembly. SUMMARY

[0006] In view of this, the present application provides a two-dimensional COFs material with large interlayer spacing and a preparation method and application thereof.

[0007] The technical scheme of the present application is as follows:

[0008] A two-dimensional COFs material with large interlayer spacing, the structure of the two-dimensional COFs material is shown in formula (I) or (II) or (III):

[0009] ,

[0010] ,

[0011] .

[0012] Further, the two-dimensional COFs material is prepared by Schiff base reaction of an aldehyde-based monomer and an amino monomer; the aldehyde-based monomer is 4,4',4'',4'''-(6,7,9,10,17,18,20,21-octahydrodi[b,k][1,4,7,10,13,16]hexaoxacyclooctadecine-2,3,13,14-tetrayl) tetrakisbenzaldehyde; and the amino monomer is selected from one of N,N,N',N'-tetrakis(p-aminophenyl)p-phenylenediamine, N1,N1'-([1,1'-biphenyl]-4,4'-diyl)bis(N1-(4-aminophenyl)benzene-1,4-diamine) and N1,N1'-([1,1':4',1''-terphenyl]-4,4''-diyl)bis(N1-(4-aminophenyl)benzene-1,4-diamine).

[0013] Further, the preparation method of the two-dimensional COFs material with large interlayer spacing comprises the following steps:

[0014] (1) Put the aldehyde monomer and the amino monomer into a reaction tube, add an organic solvent and mix to obtain a mixture;

[0015] (2) After ultrasonic treatment, the mixture is added with a catalyst for reaction, then the reaction system is frozen by a liquid nitrogen bath, deoxygenation treatment is carried out, the reaction tube is sealed after heating and crystallization, Soxhlet extraction and vacuum drying, and the target two-dimensional COFs material is obtained.

[0016] Further, the molar ratio of the aldehyde monomer to the amino monomer is 1:1-2.

[0017] Further, the organic solvent is one or more of benzyl alcohol, o-dichlorobenzene, N,N-dimethylacetamide and n-butanol; the catalyst is an aqueous acetic acid solution; and the concentration of the catalyst is 6-12 mol / L. -1 .

[0018] Further, the total mass of the aldehyde monomer and the amino monomer, the amount of the organic solvent and the amount of the catalyst are in the ratio of 40-70 mg:1.0-2.0 mL:100-200 uL.

[0019] Further, the reaction temperature of the heating crystallization is 120-160 DEG C, and the time is 3-5 days.

[0020] Further, the solvent of the Soxhlet extraction is one or more of anhydrous N,N-dimethylformamide, anhydrous N,N-dimethylacetamide, anhydrous tetrahydrofuran and anhydrous methanol; and the time of the Soxhlet extraction is 24-48 h.

[0021] Application of the two-dimensional COFs material in adsorbing thorium ions.

[0022] Further, the pH value of the thorium ion solution adsorbed by the two-dimensional COFs material is 1.0-4.0.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] (1) The present application successfully prepares a two-dimensional crown ether COFs material with good crystallinity and stable structure by taking a flexible crown ether unit as a core building block. The design makes the cavity structure of the crown ether an important part of the inherent pore of the framework, not only avoids the problem of inactivation of active sites caused by winding and stacking of flexible segments, but also ensures the high accessibility of the adsorption sites. In addition, due to the large interlayer spacing caused by the flexibility of the crown ether ring, the hydrated thorium ions can diffuse smoothly between the layers, laying a solid structural foundation for efficient transmission and selective screening of metal ions.

[0025] (2) The material retains the inherent recognition ability of the crown ether ring to specific ions, and further realizes efficient binding to thorium ions through the dual coordination between the imine bond and the crown ether unit. This unique multi-site adsorption mechanism significantly enhances the binding capacity and selectivity of the material to thorium ions, making it not only exhibit high adsorption capacity to thorium, but also show excellent selectivity and extremely high separation efficiency in thorium / uranium separation. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Powder X-ray diffraction (PXRD) spectra of the two-dimensional COFs materials prepared in Example 1, Example 4 and Example 7; wherein, Figure 1 (a) is the PXRD spectrum of the B18C6-TAPD-COF material of Example 1, Figure 1 (b) is the PXRD spectrum of the B18C6-TAB-COF material of Example 4, Figure 1 (c) is the PXRD spectrum of the B18C6-TDA-COF material of Example 7.

[0027] Figure 2 Fourier transform infrared (FT-IR) spectra of the two-dimensional COFs materials prepared in Example 1, Example 4 and Example 7; wherein, Figure 2 (a) is the FT-IR spectrum of the B18C6-TAPD-COF material of Example 1, Figure 2 (b) is the FT-IR spectrum of the B18C6-TAB-COF material of Example 4, Figure 2 (c) is the FT-IR spectrum of the B18C6-TDA-COF material of Example 7.

[0028] Figure 3 Nitrogen adsorption-desorption curves of the two-dimensional COFs materials prepared in Example 1, Example 4 and Example 7; wherein, Figure 3 (a) is the nitrogen adsorption-desorption curve of the B18C6-TAPD-COF material of Example 1, Figure 3 (b) is the nitrogen adsorption-desorption curve of the B18C6-TAB-COF material of Example 4, Figure 3 (c) is the nitrogen adsorption-desorption curve of the B18C6-TDA-COF material of Example 7.

[0029] Figure 4 Adsorption capacity and removal rate of the two-dimensional COFs materials prepared in Example 1, Example 4 and Example 7 to Th(IV) under different pH conditions.

[0030] Figure 5Adsorption isotherm plots of the two-dimensional COF materials prepared for Example 1, Example 4 and Example 7; wherein, Figure 5 (a) is an adsorption isotherm plot of the B18C6-TAPD-COF material of Example 1, Figure 5 (b) is an adsorption isotherm plot of the B18C6-TAB-COF material of Example 4, Figure 5 (c) is an adsorption isotherm plot of the B18C6-TDA-COF material of Example 7. Wherein, Langmuir represents the Langmuir adsorption isotherm model, and Freundlich represents the Freundlich adsorption isotherm model. The Langmuir model is based on the assumption that the surface of the adsorbent is uniform, the adsorption is a monomolecular layer, and there is no interaction between the adsorbed molecules. The Freundlich model is an empirical formula, which is more suitable for describing the adsorption of non-homogeneous surfaces. DETAILED DESCRIPTION

[0031] In order to better understand the technical content of the present application, the following specific examples are provided to further illustrate the present application.

[0032] The experimental methods used in the embodiments of the present application are conventional methods unless otherwise specified.

[0033] The materials, reagents, etc. used in the embodiments of the present application can be obtained from commercial channels unless otherwise specified.

[0034] The aldehyde monomer 4,4',4'',4'''-(6,7,9,10,17,18,20,21-octahydrodi[b,k][1,4,7,10,13,16]hexaoxacyclooctadecine-2,3,13,14-tetrayl) tetrakisbenzaldehyde in the present application is abbreviated as B18C6;

[0035] The amino monomer N,N,N',N'-tetrakis(p-aminophenyl)p-phenylenediamine is abbreviated as TAPD;

[0036] N1,N1'-([1,1'-biphenyl]-4,4'-diyl)bis(N1-(4-aminophenyl)benzene-1,4-diamine) is abbreviated as TAB;

[0037] N1,N1'-([1,1':4',1''-terphenyl]-4,4''-diyl)bis(N1-(4-aminophenyl)benzene-1,4-diamine) is abbreviated as TDA. The above substances are described using the corresponding abbreviations in the specific embodiments.

[0038] Preparation of B18C6-TAPD-COF of Example 1

[0039] 25 mg of B18C6 and 15.21 mg of TAPD were placed in a pressure-resistant reaction tube, and 1.0 mL of o-dichlorobenzene organic solvent was added to obtain a mixture. The mixture was then ultrasonically treated in an ultrasonic cleaner to ensure complete dissolution and homogenization. Subsequently, 0.1 mL of a 9 mol / L solution was added to the system. -1 An aqueous solution of acetic acid was prepared, and the reaction system was rapidly frozen to a solid state using a liquid nitrogen bath. Under freezing conditions, the reaction tube was evacuated and filled with high-purity nitrogen to complete the deoxygenation treatment. Then, the reaction tube was sealed under vacuum conditions and placed in a 120°C oven for a 3-day crystallization reaction. After the reaction, the solid was collected and Soxhlet extracted with a mixed solution of N,N-dimethylformamide and tetrahydrofuran (volume ratio 1:2) for 24 hours to obtain a yellow powder product, named B18C6-TAPD-COF.

[0040] Example 2: Preparation of B18C6-TAPD-COF(Ⅰ)

[0041] 25 mg of B18C6 and 30.42 mg of TAPD were placed in a pressure-resistant reaction tube, and 2.0 mL of an organic solution obtained by mixing o-dichlorobenzene and benzyl alcohol in a 1:1 volume ratio was added to obtain a mixture. The mixture was then ultrasonically treated in an ultrasonic cleaner to ensure complete dissolution and homogenization. Subsequently, 0.3 mL of a 6 mol / L solution was added to the system. -1 An aqueous solution of acetic acid was prepared, and the reaction system was rapidly frozen to a solid state using a liquid nitrogen bath. Under freezing conditions, the reaction tube was evacuated and filled with high-purity nitrogen to complete the deoxygenation treatment. Then, the reaction tube was sealed under vacuum conditions. The sealed reaction tube was placed in an oven at 140°C for 3 days. After the reaction was completed, the solid was collected, and the solid was subjected to Soxhlet extraction with tetrahydrofuran for 48 h. Finally, a yellow powder product was obtained, named B18C6-TAPD-COF(Ⅰ).

[0042] Example 3: Preparation of B18C6-TAPD-COF(II)

[0043] 25 mg of B18C6 and 22.68 mg of TAPD were placed in a pressure-resistant reaction tube, and 1.0 mL of a 1:1 mixture of o-dichlorobenzene and N,N-dimethylacetamide was added to obtain a mixture. The mixture was then ultrasonically treated to ensure complete dissolution and homogenization. Subsequently, 0.1 mL of a 6 mol / L solution was added to the system. -1mixture; the mixture was placed in an ultrasonic cleaning instrument for ultrasonic treatment to make it fully dissolved and uniformly mixed; then, 0.1 mL of an acetic acid aqueous solution with a concentration of 6 mol L-1was added to the system, and the reaction system was rapidly frozen to a solidified state by a liquid nitrogen bath; under the frozen condition, vacuumization and high-purity nitrogen filling operations were performed on the reaction tube to complete the deoxygenation treatment, and then the reaction tube was fusion-sealed under vacuum; the fusion-sealed reaction tube was placed in a 120°C oven for reaction for 3 days, and after the reaction was completed, the solid was collected, and a Soxhlet extraction of the solid was performed for 24 h using a N,N-dimethylformamide and tetrahydrofuran mixed solution (volume ratio of 1:2), and finally a yellow powder product was obtained, which was named B18C6-TAB-COF.

[0044] Example 4 Preparation of B18C6-TAB-COF

[0045] 25 mg of B18C6 and 17.66 mg of TAB were placed in a pressure-resistant reaction tube, 1.0 mL of o-dichlorobenzene was added to obtain a mixture; the mixture was placed in an ultrasonic cleaning instrument for ultrasonic treatment to make it fully dissolved and uniformly mixed; then, 0.1 mL of an acetic acid aqueous solution with a concentration of 6 mol L -1 -1was added to the system, and the reaction system was rapidly frozen to a solidified state by a liquid nitrogen bath; under the frozen condition, vacuumization and high-purity nitrogen filling operations were performed on the reaction tube to complete the deoxygenation treatment, and then the reaction tube was fusion-sealed under vacuum; the fusion-sealed reaction tube was placed in a 120°C oven for reaction for 3 days, and after the reaction was completed, the solid was collected, and a Soxhlet extraction of the solid was performed for 24 h using a N,N-dimethylformamide and tetrahydrofuran mixed solution (volume ratio of 1:2), and finally a yellow powder product was obtained, which was named B18C6-TAB-COF.

[0046] Example 5 Preparation of B18C6-TAB-COF (I)

[0047] 25 mg of B18C6 and 35.32 mg of TAB were placed in a pressure-resistant reaction tube, 2.0 mL of an organic solution of o-dichlorobenzene / n-butanol mixed in a volume ratio of 4:1 was added to obtain a mixture; the mixture was placed in an ultrasonic cleaning instrument for ultrasonic treatment to make it fully dissolved and uniformly mixed; then, 0.2 mL of an acetic acid aqueous solution with a concentration of 9 mol L -1 -1was added to the system, and the reaction system was rapidly frozen to a solidified state by a liquid nitrogen bath; under the frozen condition, vacuumization and high-purity nitrogen filling operations were performed on the reaction tube to complete the deoxygenation treatment, and then the reaction tube was fusion-sealed under vacuum; the fusion-sealed reaction tube was placed in a 140°C oven for reaction for 3 days, and after the reaction was completed, the solid was collected, and a Soxhlet extraction of the solid was performed for 48 h using a tetrahydrofuran solution, and finally a yellow powder product was obtained, which was named B18C6-TAB-COF (I).

[0048] Example 6 Preparation of B18C6-TAB-COF (II)

[0049] B18C6 and 26.49 mg of TAB were placed in a pressure-resistant reaction tube, 1.0 mL of an organic solution of o-dichlorobenzene / N,N-dimethylacetamide mixed at a volume ratio of 1:1 was added to obtain a mixture; the mixture was placed in an ultrasonic cleaner for ultrasonic treatment to fully dissolve and mix uniformly; then, 0.1 mL of an aqueous acetic acid solution with a concentration of 12 mol / L was added to the system, and the reaction system was rapidly frozen to a solidified state by a liquid nitrogen bath; under the frozen condition, the reaction tube was subjected to vacuumization and high-purity nitrogen filling to complete deoxygenation treatment, and then the reaction tube was fusion-sealed under vacuum; the fusion-sealed reaction tube was placed in a 160°C oven for reaction for 5 days, and after the reaction was completed, the solid was collected, the solid was subjected to Soxhlet extraction for 48 h using a mixed solution of tetrahydrofuran and methanol (at a volume ratio of 1:1), and finally a yellow powder product was obtained, which was named as B18C6-TAB-COF(II). -1

[0050] Example 7 Preparation of B18C6-TDA-COF

[0051] B18C6 and 20.11 mg of TDA were placed in a pressure-resistant reaction tube, 1.0 mL of o-dichlorobenzene was added to obtain a mixture; the mixture was placed in an ultrasonic cleaner for ultrasonic treatment to fully dissolve and mix uniformly; then, 0.1 mL of an aqueous acetic acid solution with a concentration of 6 M was added to the system, and the reaction system was rapidly frozen to a solidified state by a liquid nitrogen bath; under the frozen condition, the reaction tube was subjected to vacuumization and high-purity nitrogen filling to complete deoxygenation treatment, and then the reaction tube was fusion-sealed under vacuum; the fusion-sealed reaction tube was placed in a 120°C oven for reaction for 3 days, and after the reaction was completed, the solid was collected, the solid was subjected to Soxhlet extraction for 24 h using a mixed solution of N,N-dimethylformamide and tetrahydrofuran (at a volume ratio of 1:2), and finally a yellow powder product was obtained, which was named as B18C6-TDA-COF.

[0052] Example 8 Preparation of B18C6-TDA-COF(I)

[0053] B18C6 and 40.22 mg of TDA were placed in a pressure-resistant reaction tube, 2.0 mL of an organic solution of o-dichlorobenzene / n-butanol mixed at a volume ratio of 4:1 was added to obtain a mixture; the mixture was placed in an ultrasonic cleaner for ultrasonic treatment to fully dissolve and mix uniformly; then, 0.2 mL of an aqueous acetic acid solution with a concentration of 9 mol / L was added to the system, and the reaction system was rapidly frozen to a solidified state by a liquid nitrogen bath; under the frozen condition, the reaction tube was subjected to vacuumization and high-purity nitrogen filling to complete deoxygenation treatment, and then the reaction tube was fusion-sealed under vacuum; the fusion-sealed reaction tube was placed in a 160°C oven for reaction for 5 days, and after the reaction was completed, the solid was collected, the solid was subjected to Soxhlet extraction for 48 h using a mixed solution of tetrahydrofuran and methanol (at a volume ratio of 1:1), and finally a yellow powder product was obtained, which was named as B18C6-TDA-COF(II). -1 ​An aqueous solution of acetic acid was prepared, and the reaction system was rapidly frozen to a solid state using a liquid nitrogen bath. Under freezing conditions, the reaction tube was evacuated and filled with high-purity nitrogen to complete the deoxygenation treatment. Then, the reaction tube was sealed under vacuum conditions. The sealed reaction tube was placed in an oven at 140°C for 3 days. After the reaction was completed, the solid was collected, and the solid was extracted with tetrahydrofuran solution using a Soxhlet extract for 24 h. Finally, a yellow powder product was obtained, named B18C6-TDA-COF(Ⅰ).

[0054] Example 9: Preparation of B18C6-TDA-COF(II)

[0055] 25 mg of B18C6 and 30.16 mg of TDA were placed in a pressure-resistant reaction tube, and 1.0 mL of a 1:1 mixture of o-dichlorobenzene and N,N-dimethylacetamide was added to obtain a mixture. The mixture was then ultrasonically treated to ensure complete dissolution and homogenization. Subsequently, 0.1 mL of a 12 mol / L solution was added to the system. -1 An aqueous solution of acetic acid was prepared, and the reaction system was rapidly frozen to a solid state using a liquid nitrogen bath. Under freezing conditions, the reaction tube was evacuated and filled with high-purity nitrogen to complete the deoxygenation treatment. Then, the reaction tube was sealed under vacuum conditions. The sealed reaction tube was placed in an oven at 160°C for 5 days. After the reaction was completed, the solid was collected, and the solid was subjected to Soxhlet extraction for 48 h using a mixed solution of tetrahydrofuran and methanol (volume ratio of 1:1). Finally, a yellow powder product was obtained, named B18C6-TDA-COF(Ⅱ).

[0056] Experiments were conducted on the three two-dimensional COFs materials prepared in Examples 1, 4 and 7 above.

[0057] (1) Powder X-ray diffraction experiment

[0058] The powder X-ray diffraction experiment of the three two-dimensional COFs materials was performed on an XRD-SmartLab using a Cu-Ka radiation source (λ = 1.542 Å). The three two-dimensional COFs material powder samples prepared from Example 1, Example 4 and Example 7 were respectively placed in a marver and ground, 10 mg of the ground powder sample was taken with a medicine spoon and filled into the glass sample groove of the sample stage, and a glass slide was used to flatten it evenly to ensure that the surface was flush with the sample stage to prevent peak deviation. The door was unlocked, the sample stage was inserted into the bracket card slot, and after ensuring that it was fixed firmly, the door was closed and locked (confirm that the safety indicator light is on), the scanning range was input as 2°-40° in the software interface, the scanning speed was set as 10° / min, the save location and file name were set, and the "Run" button was clicked to start scanning, and the spectrum was monitored in real time. After the collection was completed, the original data was automatically saved in the.rasx format, and the original data was converted into the.txt format through the Rasx Converster. The Origin software was used for data processing. The data processing process of the Origin software is as follows:

[0059] 1. Start OriginPro, create a new blank project (Project), and automatically generate a blank worksheet (Worksheet);

[0060] 2. Click the menu bar Date → Import From File → Multiple ASCII, and select the verified.txt file;

[0061] 3. In the import dialog box, confirm that the Column Definition is: Col (A) = 2θ, Col (B) = Intensity, click OK, remove the header and unit row, and only keep the two column data, and set the columns as X Y;

[0062] 4. Select the two column data of Col (A) and Col (B) in the worksheet;

[0063] 5. Click the toolbar Plot → Basic 2D → Line to automatically generate a basic PXRD line graph.

[0064] The corresponding PXRD spectrum is shown in Figure 1 .

[0065] As shown in Figure 1 , Figure 1 (a) to (c) are respectively the PXRD spectra of the three two-dimensional COFs materials prepared from Example 1, Example 4 and Example 7. The results show that the three materials all have clear characteristic diffraction peaks, indicating that they have regular crystal structures, which confirms the successful synthesis of the target two-dimensional COFs material of the present application.

[0066] (2) Fourier transform infrared spectroscopy experiment

[0067] The Fourier transform infrared spectroscopy experiment (FT-IR) was performed on an FT / IR-6800 instrument. The stabilized power supply, optical bench main machine and computer were turned on in turn, the operation software was started, and the light source was preheated for 30 minutes to stabilize. The parameters were set as follows: scanning range 4000~400 cm -1 , resolution 4 cm -1 , scanning times 16 times; click "Collect background" to save the spectrum. Using ATR method, three kinds of two-dimensional COFs material powder samples prepared by example 1, example 4 and example 7 were placed on the surface of diamond crystal and compacted. Select "Collect sample" to start scanning; real-time monitoring of the spectrum, save the original data as.txt format after collection, and use Origin software for data processing. The data processing process of Origin software is as follows:

[0068] 1. Start OriginPro, create a blank project (Project), and automatically generate a blank worksheet (Worksheet);

[0069] 2. Click Date → Import From File → Multiple ASCII, select the exported FT-IR.txt file;

[0070] 3. Import settings: confirm Col (A)=wavenumber (cm - ¹), Col (B)=absorbance (Abs), remove header and unit row, and only keep two columns of data, and set column as X Y;

[0071] 4. Select Col (A) (wavelength) and Col (B) (absorbance);

[0072] 5. Click toolbar Plot → Basic 2D → Line to generate FT-IR spectrum.

[0073] The corresponding FT-IR spectrum is shown in Figure 2 .

[0074] Figure 2 The FT-IR spectrum of three kinds of COFs materials. The results show that the characteristic absorption peaks of amino and aldehyde groups in the raw materials after reaction disappear completely, and obvious imine bond (C=N) stretching vibration absorption peaks appear at the corresponding wavenumber, which further verifies the successful construction of COFs materials.

[0075] (3) Nitrogen adsorption and desorption experiment

[0076] Nitrogen adsorption-desorption experiments were performed on an Autosorb iQ gas adsorption instrument. Turn on the instrument host, vacuum system and computer in turn, start the operation software, vacuum the system and check the gas circuit for leaks. Connect the sample tubes filled with Example 1, Example 4 and Example 7 to the degassing station, set the drying program to a temperature of 120°C and a time of 12 hours, and perform drying and degassing pretreatment under vacuum conditions. After degassing is complete, cool the sample tube and transfer it to the analysis station. Then, wrap the cold trap filled with liquid nitrogen around the sample tube and perform nitrogen adsorption-desorption testing at 77K: set the relative pressure range to 0.01-0.995, the system automatically steps in nitrogen and monitors the equilibrium adsorption at each pressure point, and the complete adsorption-desorption isotherm is obtained. Save the raw data in.QPS format after collection, use the ASiQwin software provided with the instrument to analyze the BET specific surface area. Save the raw data in.txt format after collection, use Origin software for data processing. The Origin software data processing process is as follows:

[0077] 1. Start OriginPro, create a new blank project (Project), and automatically generate a blank worksheet (Worksheet);

[0078] 2. Enter the adsorption and desorption data in the processed BET.txt in turn;

[0079] 3. Confirm that Col (A) is the adsorption Relative pressure (P / P0), Col (B) is the adsorption N2uptake (cm 3 ×g -1 ), Col (C) is the desorption Relative pressure (P / P0), Col (D) is the desorption N2uptake (cm 3 ×g -1 ), and set the column to XY XY;

[0080] 4. Select Col (A), Col (B), Col (C), and Col (D);

[0081] 5. Click the toolbar Plot → Basic 2D→Line+ Symbol to generate a nitrogen adsorption-desorption curve graph, as Figure 3 shown.

[0082] Figure 3 Nitrogen adsorption-desorption curves of three kinds of two-dimensional COFs materials. The results show that the three materials all exhibit a large specific surface area, providing sufficient adsorption sites for subsequent adsorption applications.

[0083] Example 10 Adsorption experiment of two-dimensional COFs material on thorium at different pH values

[0084] To explore the influence of solution pH value on the adsorption behavior of two-dimensional COFs material on Th(IV) ions, the two-dimensional COFs materials prepared in Examples 1, 4, and 7 were subjected to adsorption performance tests at different pH values. The specific experimental process is as follows:

[0085] 2w / v% pure nitric acid aqueous solution was used as a blank solution for instrument baseline calibration.

[0086] At room temperature, thorium nitrate and 1 M nitric acid solution were used to prepare a thorium ion solution with an initial concentration of 1000 mg L -1 as a thorium standard stock solution.

[0087] 5 mL of the thorium standard stock solution was taken and diluted with water, and then 0.1 mol L - ¹ nitric acid solution or 0.1 mol L - ¹ sodium hydroxide solution was added dropwise, the pH of the solution was adjusted to 1, 2, 3, and 4, and finally diluted to 50 mL to prepare four kinds of 100 mg L -1 adsorption solutions under different pH conditions; then 2 mg of the two-dimensional COFs material prepared in Examples 1, 4, and 7 was taken and mixed with 6 mL of the adsorption solution with different pH values for 24 h to obtain a sample solution, which was filtered with a 0.22 μm filter membrane, 1.0 mL of the filtered sample solution was taken, and 9.0 mL of 2% HNO3 aqueous solution was added for 10-fold dilution to prepare the final sample solution to be tested.

[0088] 2w / v% HNO3 aqueous solution was used as the matrix to prepare a series of standard solutions with concentrations of 0.5, 1.0, 2.5, 5.0, and 10.0 mg L -1 for establishing a calibration curve.

[0089] The matrix of all solutions was kept at a consistent acidity to effectively eliminate matrix interference and ensure the accuracy and reliability of the analysis process.

[0090] The mass concentration of thorium in the initial solution and the sample solution to be tested before and after adsorption was tested using an inductively coupled plasma emission spectrometer (Jenway Plasma 3000 type ICP-OES), and the adsorption amount and removal rate of thorium were calculated according to the formula, and the experimental results are shown in Figure 4 .

[0091] The ICP-OES determination process is as follows:

[0092] Turn on the regulated power supply, circulating water system (water temperature 22-25℃), exhaust equipment, and argon main valve (partial pressure 0.6-0.8 MPa) in sequence; start the main power supply and operating software, preheat for 30 minutes, install the peristaltic pump tubing, and check the gas path sealing and whether the liquid inlet and outlet are normal. Confirm that the photocell temperature is stable at 38℃ and the detector temperature is stable at -35℃. Click "Ignition" in the software and observe that the flame is a stable white cone shape. Preheat for 20 minutes; optimize the parameters: RF actuator power 1200W, carrier gas flow rate 0.65 L / min. -1 0.5 L / min of auxiliary gas -1 The exposure time was 8 s, the injection time was 51 s, and the observation mode was radial. An analytical method was established, elemental spectral lines were selected, and standard concentrations were set (6 points, covering the concentration range of the sample solution to be tested). The test sequence was blank solution, series of standard solutions, and sample solution to be tested; all samples were tested three times.

[0093] During instrument operation, the software monitors and acquires signals in real time. The instrument automatically measures the blank solution and a series of standard solutions to generate a calibration curve. Subsequently, all sample solutions are measured sequentially to directly obtain quantitative data of the target components in each sample. After all data acquisition is complete, the raw data file is saved. Further processing, analysis, and plotting of the raw data are then performed. Among these steps:

[0094] Adsorption capacity calculation formula: ,

[0095] Removal rate calculation formula: ,

[0096] In the formula: q e The adsorption capacity of thorium at adsorption equilibrium (mg g) -1 η is the removal rate (%), and C0 is the initial thorium concentration in the solution (mg / L). -1 ), C e To balance the mass concentration of thorium in the solution (mg / L) -1 V is the volume of the initial solution added to the sample solution (L), and m is the mass (mg) of the two-dimensional COFs materials prepared in Examples 1, 4, and 7 added to the sample solution.

[0097] The raw concentration data obtained from ICP-OES is multiplied by 10 to obtain the true adsorption data. This data is then converted using the adsorption capacity calculation formula and the removal rate formula to obtain the corresponding adsorption performance data (such as adsorption capacity, removal rate, etc.). Data processing is performed using Origin software. The specific process for data processing using Origin software is as follows:

[0098] 1. Start OriginPro, create a new project and a blank worksheet;

[0099] 2. Input the calculated adsorption data in order of pH;

[0100] 3. Confirm that Col (A) is pH (1, 2, 3, 4 respectively), Col (B) is the adsorption capacity of B18C6-TAPD-COF, Col (C) is the adsorption capacity of B18C6-TAB-COF, Col (D) is the adsorption capacity of B18C6-TDA-COF, Col (E) is the removal rate of B18C6-TAPD-COF, Col (F) is the removal rate of B18C6-TAB-COF, Col (G) is the removal rate of B18C6-TDA-COF;

[0101] 4. In the worksheet, select Col (A) (pH) and the adsorption capacity data columns Col (B), Col (C), Col (D) at the same time. Click Plot → Column / Bars → Grouped Columns. At this time, a grouped column chart with pH as the X axis and adsorption capacity as the left Y axis will be generated;

[0102] 5. In the activated state of the generated graph window, click Insert→New Layer (Axes)→Right-Y in the top menu bar to add a new layer with an independent right Y axis;

[0103] 6. When Layer 2 is activated, click Graph→Add Plot to Layer→Line in the menu bar. Select X as the pH data of Col (A), and select Y as the removal rate data columns Col (E), Col (F), Col (G). Click OK, and the removal rate line chart will be added to the right Y axis, obtaining a two-dimensional COFs material adsorption capacity and removal rate graph under different pH conditions for Th(Ⅳ).

[0104] The experimental results are shown in Figure 4 The adsorption curve of Th(Ⅳ) under different pH conditions shows that the adsorption performance of the two-dimensional COFs material prepared in Example 1, Example 4 and Example 7 changes dramatically with the increase of pH. When the pH value increases from 1.0 to 3.0, the adsorption capacity only increases slowly; however, at pH=4.0, the adsorption curve shows a sudden jump, the adsorption capacity reaches the peak value, and the removal rate of Th(Ⅳ) reaches 100%, indicating that a high-efficiency adsorption process occurs near the critical pH point.

[0105] Example 11 Competitive ion selectivity experiment

[0106] Based on the pH adsorption performance test results, Example 10 shows that the two-dimensional COFs material exhibits a high adsorption affinity for Th(Ⅳ) at pH = 4.0. Therefore, to evaluate its selective adsorption capacity in complex systems, a competitive ion adsorption experiment was conducted at pH = 4.0. A mixed solution containing Th(Ⅳ) and various competing ions (including lithium Li(I), palladium Pd(II), uranium U(VI), lanthanum La(III), praseodymium Pr(III), samarium Sm(III), gadolinium Gd(III), and lutetium Lu(III)) was prepared, with an initial concentration of 50 mg / L for each ion. -1 2.0 mg of the two-dimensional crown ether COFs materials prepared in Examples 1, 4, and 7 were accurately weighed and added to 6.0 mL of the above mixed solution, respectively. The mixture was stirred at a constant temperature for 24 h to ensure adsorption equilibrium. Subsequently, the concentrations of each ion before and after adsorption were determined using the ICP-OES method of Example 10, and the thorium / uranium separation factor SF was calculated using the formula. Th / U The results are summarized in Table 1. Among them:

[0107] Allocation coefficient:

[0108] Separation factor:

[0109] In the formula, C0 is the initial thorium concentration in the solution (mg / L). -1 ), C e To balance the mass concentration of thorium in the solution (mg / L) -1 V is the initial volume of the solution added to the sample solution (L), and m is the mass of the two-dimensional COFs material added to the sample solution (mg). The partition coefficient of thorium ions (mL g) -1 ); The partition coefficient of competing metal ions (mL g) -1 );

[0110] Table 1 Selectivity of 2D COFs materials for thorium / uranium separation under the presence of competing ions. Th / U

[0111]

[0112] As shown in Table 1, at pH = 4.0, Th(Ⅳ) and the initial concentration of each competing ion (including lithium Li(I), palladium Pd(II), uranium U(VI), lanthanum La(Ⅲ), praseodymium Pr(Ⅲ), samarium Sm(Ⅲ), gadolinium Gd(Ⅲ), and lutetium Lu(Ⅲ)) was 50 mg / L. -1Under the specified conditions, the three two-dimensional COFs materials (Examples 1, 4, and 7) all exhibited excellent selective adsorption capacity for Th(Ⅳ). The materials showed low adsorption capacity for competing ions other than thorium, but high adsorption capacity for Th(Ⅳ). Table 1 shows the Th / U separation factor SF of the three two-dimensional COFs materials. Th / U The values ​​were as high as 241.63 (Example 1), 222.14 (Example 4), and 148.35 (Example 7), respectively. These data fully demonstrate that this series of two-dimensional COFs materials can efficiently and selectively separate and enrich thorium from complex multi-ion systems.

[0113] Example 12 Adsorption isotherm experiment of thorium in two-dimensional COFs materials

[0114] To quantitatively evaluate the maximum adsorption capacity of two-dimensional COFs materials for Th(Ⅳ), adsorption isotherm experiments were conducted under the previously optimized pH conditions (pH = 4.0). At room temperature, initial concentrations of 25, 50, 75, 100, 150, 200, 300, 400, 500, and 600 mg L were prepared at pH 4. -1 For the Th(Ⅳ) solutions, 2.0 mg of each of the two-dimensional COFs materials prepared in Examples 1, 4, and 7 were weighed and placed in 6.0 mL of Th(Ⅳ) solutions of different concentrations, and stirred for 24 h. Subsequently, the Th(Ⅳ) ion concentration in the solution after 24 h of adsorption was measured according to the ICP-OES determination method of Example 10, the adsorption amount was calculated, and adsorption isotherms were plotted. The adsorption isotherms are shown below. Figure 5 As shown.

[0115] The adsorption isotherm plot was drawn using Origin software. The specific data processing steps in Origin software are as follows:

[0116] 1. Launch OriginPro, create a new blank project, and a blank worksheet will be automatically generated.

[0117] 2. Name the data column. Set Col(A) to C. e (mg L -1 Col(B) is q e (mg g -1 );

[0118] 3. Calculate C e With q e The data were entered into Col(A) and Col(B) sequentially. Click the top menu Plot→Basic 2D→Scatter to generate a scatter plot of the experimental data;

[0119] 4. Select the data in the figure and perform nonlinear curve fitting (Langmuir and Freundlich models) to obtain adsorption isotherm plots.

[0120] like Figure 5 As shown, under pH = 4.0, all three two-dimensional COF materials exhibited extremely high adsorption capacities for Th(Ⅳ). According to the Langmuir adsorption isotherm model, the saturated adsorption capacities of Example 1 (B18C6-TAPD-COF), Example 4 (B18C6-TAB-COF), and Example 7 (B18C6-TDA-COF) were 1496 mg g, respectively. -1 1342 mg g -1 and 1233 mg g -1 .

[0121] Comparative Example 1

[0122] 25 mg of 4,4',4'',4'''-(6,7,9,10,17,18,20,21-octahydrodi[b,k][1,4,7,10,13,16]hexaoxane-octadecene-2,3,13,14-tetrayl)tetrabenzaldehyde (B18C6) and 15.2 mg of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) were placed in a pressure-resistant reaction tube, and 1 mL of a 1:1 mixture of o-dichlorobenzene and n-butanol was added to obtain a mixture. The mixture was ultrasonically treated in an ultrasonic cleaner to ensure complete dissolution and homogenization. Subsequently, 0.1 mL of 6M acetic acid aqueous solution was added to the system, and the reaction system was rapidly frozen to a solid state using a liquid nitrogen bath. Under freezing conditions, the reaction tube was evacuated and purged with high-purity nitrogen. After deoxygenation, the reaction tube was sealed under vacuum. The sealed reaction tube was placed in a 120°C oven for 3 days. After the reaction, the solid was collected and thoroughly washed with N,N-dimethylformamide and tetrahydrofuran to obtain the final material, named B18C6-TAPT. No obvious sharp diffraction peaks were observed in the X-ray diffraction pattern of this sample, indicating that the obtained material lacks a long-range ordered crystal structure and is mainly amorphous, failing to successfully form crystalline COFs material.

[0123] Comparative Example 2

[0124] A mixture was prepared by placing 14 mg of 2,3,5,6,8,9-hexahydrobenzo[B][1,4,7,10]tetraoxacyclododecane-11,14-dicarboxaldehyde (CE) and 12 mg of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) into a pressure tube, adding 1 mL of a mixture of o-dichlorobenzene / n-butanol in a volume ratio of 1:1, and then ultrasonically treating the mixture in an ultrasonic cleaner to fully dissolve and mix the mixture. Subsequently, 0.1 mL of 6M aqueous acetic acid was added to the system, and the reaction system was rapidly frozen to a solidified state by a liquid nitrogen bath. Under the frozen condition, the reaction tube was subjected to vacuumization and nitrogen filling. After the deoxygenation treatment was completed, the reaction tube was sealed under vacuum. The sealed reaction tube was placed in a 120°C oven for reaction for 3 days. After the reaction was completed, the solid was collected and washed with methanol three times, and finally a two-dimensional COFs material containing a 12-crown-4 group was obtained, which was named CE-COF-1. Similarly, the two-dimensional COFs material prepared in this example was used for the adsorption isotherm experiment of thorium, and the specific process of the experiment was referred to in Example 12. The maximum adsorption capacity was 448 mg g -1 .

[0125] Example 3

[0126] A mixture was prepared by placing 12.3 mg of 2,4,6-trimethyl-1,3,5-triazine (TMT) and 20.1 mg of terephthaldehyde (TPA) into a pressure tube, adding 4 mL of a mixture of mesitylene / methanol in a volume ratio of 1:7 and sodium hydroxide (8.75 mg), and then ultrasonically treating the mixture in an ultrasonic cleaner to fully dissolve and mix the mixture. The reaction system was rapidly frozen to a solidified state by a liquid nitrogen bath. Under the frozen condition, the reaction tube was subjected to vacuumization and nitrogen filling. After the deoxygenation treatment was completed, the reaction tube was sealed under vacuum. The sealed reaction tube was placed in a 180°C oven for reaction for 5 days. After the reaction was completed, the solid was collected and washed with water and tetrahydrofuran three times in turn, and then was extracted in tetrahydrofuran for 24 h. Finally, a two-dimensional COFs material connected by carbon-carbon double bonds in the form of a yellow powder was obtained, which was named TMT-TPA-COF. Similarly, the two-dimensional COFs material prepared in this example was used for the adsorption isotherm experiment of thorium, and the specific process of the experiment was referred to in Example 12. The maximum adsorption capacity was 353 mg g -1 .

[0127] Example 4

[0128] Put 27 mg of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) and 13.3 mg of 2,5-dihydroxyterephthaldehyde (DHA) in a pressure-resistant reaction tube, add 1 mL of a mixture of o-dichlorobenzene / n-butanol in a volume ratio of 1:1 to obtain a mixture; the mixture is placed in an ultrasonic cleaner for ultrasonic treatment to make it fully dissolved and uniformly mixed; then, 0.1 mL of 6M acetic acid aqueous solution is added to the system, and the reaction system is rapidly frozen to a solid state by a liquid nitrogen bath; under the frozen condition, the reaction tube is subjected to vacuum pumping and high-purity nitrogen filling to complete the deoxygenation treatment, and then the reaction tube is fusion sealed under vacuum; the fusion sealed reaction tube is placed in a 120℃ oven for reaction for 3 days, and after the reaction is completed, the solid is collected and sequentially washed with tetrahydrofuran, N,N-dimethylformamide and acetone solution, and finally a two-dimensional COFs material connected by imine bonds and in the form of purple powder is obtained, which is named as TAPP-DHA-COF. Similarly, the two-dimensional COFs material prepared by using the comparative example is used for thorium adsorption isotherm experiment, and the specific process of the experiment is referred to in Example 12, and the maximum adsorption capacity is 497 mg g -1 .

[0129] Table 2 Saturation adsorption capacity of different two-dimensional COFs materials for thorium

[0130]

[0131] It can be known from Example 12, Comparative Example 2, Comparative Example 3 and Comparative Example 4 that the three two-dimensional COFs materials prepared in Example 1, Example 4 and Example 7 exhibit excellent high adsorption capacity and high selectivity for thorium ions. Compared with the two-dimensional COFs material containing 12-crown-4 ether groups (imine bond connected CE-COF-1) in Comparative Example 2 and the two-dimensional COFs materials without crown ether groups (including TMT-TPA-COF based on double bond connection and TAPP-DHA-COF based on imine bond connection) in Comparative Example 3 and Comparative Example 4, the adsorption performance is significantly improved, which fully proves the dual adsorption effect of imine bond and 18-crown-6 ether group. The introduction of crown ether constructs a stable framework with large interlayer spacing, realizing efficient capture and selective recognition of thorium ions. At the same time, the rich imine bond as a hard base can be strongly chemically coordinated with Th ions (hard acid) through “hard-soft”. Therefore, the two-dimensional COFs material in the application exhibits great application potential in the field of efficient adsorption and separation of radionuclide thorium.

[0132] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A two-dimensional COFs material with large interlayer distance, characterized in that, The structure of the two-dimensional COFs material is shown in formula (I), (II), or (III): ， ， 。 2. The method for preparing the large-interlayer-spacing two-dimensional COFs material according to claim 1, characterized in that, The two-dimensional COFs material is prepared by a Schiff base reaction of an aldehyde monomer and an amino monomer; the aldehyde monomer is 4,4',4'',4'''-(6,7,9,10,17,18,20,21-octahydrodi[b,k][1,4,7,10,13,16]hexaoxane-octadecene-2,3,13,14-tetramethyl)tetrabenzaldehyde; the amino monomer is selected from N,N,N',N'-tetra(p-aminophenyl)p-phenylenediamine, N1,N1'-([1,1'-biphenyl]-4,4'-diyl)bis(N1-(4-aminophenyl)phenyl-1,4-diamine) and N1,N1'-([1,1':4',1''-terphenyl]-4,4''-diyl)bis(N1-(4-aminophenyl)phenyl-1,4-diamine).

3. The method for preparing a large-interlayer-spacing two-dimensional COFs material according to claim 2, characterized in that, Specifically, the following steps are included: (1) Place the aldehyde monomer and the amino monomer in a reaction tube, add an organic solvent and mix well to obtain a mixture; (2) After ultrasonic treatment of the mixture, a catalyst is added to react, and then the reaction system is frozen by liquid nitrogen bath and deoxygenation treatment is carried out. The reaction tube is sealed under vacuum conditions and then heated for crystallization, Soxhlet extraction and vacuum drying to obtain the target two-dimensional COFs material.

4. The method for preparing a large-interlayer-spacing two-dimensional COFs material according to claim 3, characterized in that, The molar ratio of the aldehyde monomer to the amino monomer is 1:1~2.

5. The method for preparing a large-interlayer-spacing two-dimensional COFs material according to claim 3, characterized in that, The organic solvent is one or more of benzyl alcohol, o-dichlorobenzene, N,N-dimethylacetamide, n-butanol; the catalyst is aqueous acetic acid; the concentration of the catalyst is 6-12 mol / L -1 .

6. The method for preparing a large-interlayer-spacing two-dimensional COFs material according to claim 3, characterized in that, The ratio of the total mass of the aldehyde monomer and the amino monomer, the amount of organic solvent, and the amount of catalyst is 40~70 mg: 1.0~2.0 mL: 100~200 uL.

7. The method for preparing a two-dimensional COFs material with a large interlayer spacing according to claim 3, characterized in that, The reaction temperature for the heating crystallization is 120~160℃, and the time is 3~5 days.

8. The method for preparing a large-interlayer-spacing two-dimensional COFs material according to claim 3, characterized in that, The solvent for Soxhlet extraction is one or more of anhydrous N,N-dimethylformamide, anhydrous N,N-dimethylacetamide, anhydrous tetrahydrofuran, and anhydrous methanol; the extraction time is 24-48 h.

9. The application of the two-dimensional COFs material according to claim 1 or the two-dimensional COFs material prepared by any one of claims 2-8 in the adsorption of thorium ions.

10. The application according to claim 9, characterized in that, The pH value of the solution in which the two-dimensional COFs material adsorbs thorium ions is 1.0~4.0.

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