A reverse-stacked tf-pa-cooh cof material, and preparation method and application thereof

Abstract

The application discloses a reverse stacking TF-PA-COOH COF material and a preparation method and application thereof. The preparation method of the reverse stacking TF-PA-COOH COF material comprises the following steps: adding an aldehyde group monomer, an amino monomer and an organic solvent into a reaction tube, and ultrasonic treatment to obtain a mixture; then adding a catalyst into the mixture, freezing in liquid nitrogen, vacuumizing the tube and filling nitrogen repeatedly for three times, flame sealing the tube, cooling to 20-25 DEG C, and then heating and crystallizing, collecting the solid, washing, suction filtering and vacuum drying, so that the reverse stacking TF-PA-COOH COF material is obtained. The monomer carboxyl functional group is reversely stacked in adjacent layers to construct a hydrogen bond interaction cavity with a spacing of 7.2 angstroms between layers, and a large number of Lewis basic active chemical coordination sites (imine bond C=N and carboxyl COOH) are present in the layer, and the saturation adsorption amount of the material to thorium is as high as 2495mg g ‑1 .

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, and in particular to a reverse-stacked TF-PA-COOH COF material, its preparation method, and its application. Background Technology

[0002] With the rapid development of the nuclear energy industry, thorium, as a promising nuclear fuel resource, plays a crucial strategic role in the efficient separation and recovery of thorium for closed-loop nuclear fuel recycling, radioactive waste treatment, and environmental protection. However, achieving precise and efficient separation of thorium from complex nuclear fuel reprocessing liquids or environmental water samples remains a significant challenge. This is because thorium in the aqueous phase typically exists as a highly hydrated, large-volume Th... 4+ It exists in ionic or hydrated hydroxyl complex form, and its chemical properties are similar to those of common coexisting metal ions (such as UO2). 2+ The similarity of thorium (rare earth elements, lanthanides) makes it difficult to improve the selectivity of thorium separation.

[0003] To date, various physical and chemical methods for extracting thorium from aqueous solutions have been studied, including ion exchange, membrane separation, and adsorption. Among them, adsorption has attracted much attention due to its advantages such as simple operation, low cost, green environmental protection, and strong adaptability. Various solid adsorption materials, such as ion exchange resins, activated carbon, zeolites, and metal-organic frameworks (MOFs), have been extensively studied. COF materials, due to their advantages such as designable structure, high porosity, and good chemical stability, have shown great potential in the field of adsorption and separation. Current research mainly improves adsorption performance by introducing functional groups with affinity for target ions into the pore walls of functionalized COFs. However, the design of COF materials for efficient capture of thorium ions still has the following obvious shortcomings: (1) Lack of spatial adaptability: Most functionalization strategies only focus on the coordination ability of the functional groups themselves and ignore the thorium ions (Th) after hydrolysis. m (OH) r (4m-r)+ (1) It has a large kinetic diameter (>5.0 Å). The interlayer spacing of conventional two-dimensional COF is about 3~4 Å, which cannot provide sufficient, low-steric-resistance entry channels and binding space for these large-sized ions, resulting in low utilization of effective active sites and slow kinetics. (2) Single interaction mode: Existing materials mostly rely on single coordination interactions (such as electrostatics, coordination bonds) for capture, which makes it difficult to achieve strong selective recognition of thorium in a multi-ion competitive environment. As a bifunctional Lewis base, the carboxyl group (-COOH) can act as an active coordination site to strongly coordinate with thorium ions with Lewis acidity, and can also act as a hydrogen bond acceptor to form a multi-layered and strong hydrogen bond network with the hydroxyl groups carried by the hydrolyzed thorium ions. For example, in a thorium solution with pH=4.0, thorium mainly exists as Th(OH)3 +In this form, when carboxyl-functionalized COF materials are added to a thorium solution, the oxygen atom of the COOH group can react with Th(OH)3. + The three hydroxyl groups (OH) in the COF form hydrogen bonds, which greatly enhances the binding strength and selectivity. However, there is still a lack of systematic design on how to precisely control the spatial arrangement of carboxyl groups in the COF skeleton to synergistically exert its dual functions of chemical coordination and hydrogen bonding. (3) Limited distribution of adsorption sites: The adsorption sites of traditional functionalized COFs are mostly concentrated in the pores of the two-dimensional plane, which makes it difficult to achieve synergistic capture in three-dimensional space, thus limiting the further improvement of its theoretical adsorption capacity.

[0004] In view of the shortcomings of existing adsorbents in terms of spatial adaptability, mechanism of action and site distribution, there is an urgent need to explore a new COF adsorbent material that can achieve interlayer spatial adaptability and multi-site synergistic effect through precise structural design, in order to achieve thorium adsorption effect with high adsorption capacity, rapid equilibrium, high selectivity and excellent structural stability. Summary of the Invention

[0005] To address the aforementioned deficiencies in the prior art, this invention proposes a reverse-stacked TF-PA-COOH COF material, its preparation method, and its applications, thereby resolving the problems raised in the background section.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The TF-PA-COOH COF material exhibits an anti-overlapping stacked structure, where the -COOH units between adjacent layers are arranged in opposite directions and are in symmetrical positions. Its structure incorporates bifunctional carboxyl groups, creating multiple, synergistic adsorption sites between layers to achieve high-capacity, high-selectivity, and rapid thorium adsorption. This invention not only provides new ideas for the design and control of the microstructure of adsorbent materials but also offers a new approach for preparing highly efficient thorium adsorbents.

[0008] A reverse-stacked TF-PA-COOH COF material, the structural formula of which is shown in (I):

[0009] .

[0010] Preferably, the preparation method of the reverse stacked TF-PA-COOH COF material includes the following steps: adding aldehyde monomer, amino monomer and organic solvent to a reaction tube, and ultrasonically treating to obtain a mixture; then adding a catalyst to the mixture, freezing it in liquid nitrogen, evacuating the tube and purging it with nitrogen three times, sealing the tube with a flame, cooling it to 20-25°C and then heating it to crystallize, collecting the solid, washing and filtering the solid and vacuum drying it to obtain the reverse stacked TF-PA-COOH COF material.

[0011] Preferably, the aldehyde monomer is 1,3,5-tris(4-formylphenyl)benzene, and the amino monomer is 2,5-diaminobenzoic acid.

[0012] Preferably, the organic solvent is selected from any one of the following: a mixed solution of o-dichlorobenzene and n-butanol in a volume ratio of 1:(1-3), a mixed solution of mesitylene and ethanol in a volume ratio of 1:(1-10), or a mixed solution of mesitylene and 1,4-dioxane in a volume ratio of 1:(1-10).

[0013] Preferably, the molar ratio of aldehyde monomer to amino monomer in the mixture is 2 mmol:(1-3) mmol. The ratio of the volume of the organic solvent to the sum of the masses of the two monomers, aldehyde monomer and amino monomer, is 1 mL:(24.8-37.1) mg.

[0014] Preferably, the ultrasonic treatment time is 10-30 minutes.

[0015] Preferably, the catalyst is a 3-6 mol / L acetic acid solution, and the molar ratio of the aldehyde monomer to the volume of the catalyst is 1 mmol: 5 mL.

[0016] Preferably, the temperature for heating and crystallization is 25-120℃, and the reaction time is 3-7 days; the temperature for vacuum drying is 80-120℃, and the drying time is 12-24 hours.

[0017] Preferably, the solvent for the solid washing is at least one of anhydrous tetrahydrofuran (AR, ≥99.5%), acetone (AR, ≥99.5%), methanol (AR, ≥99.5%), and N,N-dimethylformamide (AR, ≥99.5%).

[0018] Preferably, the application of the reverse-stacked TF-PA-COOH COF material involved in this application in the selective adsorption and separation of thorium ions.

[0019] Preferably, the pH of the solution environment in which thorium ions are selectively adsorbed and separated is 2.0-5.0.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] (1) This invention constructs a two-dimensional covalent organic framework with a carboxyl group reverse stacking structure through molecular design. The interlayer spacing of the carboxyl groups arranged on the same side for building hydrogen bonding is adjusted to 7.2 Å, creating a cavity suitable for large-sized hydrated thorium ions after hydrolysis. This solves the problem of poor accessibility to thorium ions and slow adsorption kinetics of traditional two-dimensional functional COF materials due to the small interlayer spacing between adjacent layers (usually 3-4 Å).

[0022] (2) This invention utilizes the dual-function property of the carboxyl group as both a Lewis base and a hydrogen bond acceptor to achieve a synergistic effect of hydrogen bonding and chemical coordination in an anti-stacking structure. The dual mechanism greatly enhances the binding force and selectivity.

[0023] (3) The stacking method described in this invention constructs four characteristic adsorption sites in three-dimensional space, forming a multi-site synergistic adsorption environment. This breaks through the bottleneck of the single and limited distribution of adsorption sites in traditional functionalized COFs, realizes multiple bonding of thorium ions, and significantly improves the adsorption capacity;

[0024] (4) The material of this invention exhibits excellent selective adsorption performance for the radionuclide thorium, with a saturated adsorption capacity of up to 2495 mg g for thorium. -1 Experiments show that it is effective in environments containing high concentrations of competing ions (such as UO2). 2+ In complex water bodies containing various metal ions, the partition coefficient (K) of thorium d It can exceed 7.2×10 4 mL g -1 The separation factor for other competing ions reached 214~7.2×10⁻⁶. 4 This enables the selective adsorption of thorium. Attached Figure Description

[0025] Figure 1 This is a synthetic route diagram of the COF material prepared in Example 1 of the present invention;

[0026] Figure 2 Image of a COF material prepared in Example 1 of this invention;

[0027] Figure 3 Image of a COF material prepared in Example 2 of this invention;

[0028] Figure 4 Image of a COF material prepared in Example 3 of this invention;

[0029] Figure 5 The PXRD spectrum of the COF material prepared in Example 1 of this invention;

[0030] Figure 6 The image shows the FT-IR spectrum of the COF material prepared in Example 1 of this invention.

[0031] Figure 7 The image shows a SEM image of the COF material prepared in Example 1 of this invention.

[0032] Figure 8 The graph shows the adsorption capacity and removal rate of Th(IV) by the COF material prepared in Example 1 of this invention under different pH conditions.

[0033] Figure 9 This is the adsorption isotherm diagram of the COF material prepared in Example 1 of the present invention;

[0034] Figure 10 This is a graph showing the adsorption capacity of the multi-component competing ions in the COF material prepared in Example 1 of this invention. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical content of the present invention, the technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0036] The names, purchase channels, and product numbers of the commercial reagents involved in this application are as follows: (1) 1,3,5-tris(4-formylphenyl)benzene (purchased from Jiangsu Aikon Biomedical R&D Co., Ltd., product number 1181638-5g); (2) 2,5-diaminobenzoic acid (purchased from Weifang Xiaoyuan Chemical Trade Co., Ltd., product number D304132-1g); (3) p-phenylenediamine (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., product number P108424-25g); (4) tetra(4-amino)benzene (5) Phenylene adamantane (purchased from Shanghai Bide Pharmaceutical Technology Co., Ltd., item number BD01102078); (6) Terephthalaldehyde (purchased from Zancheng (Tianjin) Technology Co., Ltd., item number MJ01001); (7) 1,3,5-tricarboxyloyl phloroglucinol (purchased from Shanghai Bide Pharmaceutical Technology Co., Ltd., item number BD626553); (8) 2,5-diaminoterephthalic acid (purchased from Jiangsu Aikon Biomedical R&D Co., Ltd., item number AK0033B2-1g).

[0037] The abbreviations of the commercial reagents involved in this application are as follows: (1) Aldehyde monomer: 1,3,5-tris(4-formylphenyl)benzene is abbreviated as TF; (2) Amino monomer: 2,5-diaminobenzoic acid is abbreviated as PA-COOH; (3) p-phenylenediamine is abbreviated as PPD; (4) tetra(4-aminophenyl)adamantane is abbreviated as TAPA; (5) terephthalaldehyde is abbreviated as PTA; (6) 1,3,5-triformylphloroglucinol is abbreviated as Tp; (7) 2,5-diaminoterephthalic acid is abbreviated as DABA.

[0038] Example 1: Synthesis of TF-PA-COOH-COF

[0039] TF (15.62 mg, 0.04 mmol) and PA-COOH (9.13 mg, 0.06 mmol) were added to a Piezerx tube. 0.5 mL of o-dichlorobenzene and 0.5 mL of n-butanol were added, and the mixture was sonicated for 30 min to obtain a homogeneous mixture. Then, 0.2 mL of 5 mol / L acetic acid catalyst was added to the mixture. The Piezerx tube was placed in liquid nitrogen for freezing, and the mixture was evacuated and purged with nitrogen three times using a vacuum pump. The tube was then flame-sealed, cooled to 25°C, and placed in a 120°C oven for 3 days. After the reaction, the mixture was extracted with anhydrous tetrahydrofuran for 12 h, and then vacuum-dried at 120°C for 24 h to obtain a reddish-brown powder, named TF-PA-COOH COF. The synthetic route is shown below. Figure 1 As shown, the sample image of the material is as follows. Figure 2 As shown.

[0040] Example 2 Synthesis of TF-PA-COOH-COF

[0041] TF (15.62 mg, 0.04 mmol) and PA-COOH (3.04 mg, 0.02 mmol) were added to a Piezerx tube. 0.3 mL of trimethylbenzene and 0.3 mL of 1,4-dioxane were added as organic solvents, and the mixture was sonicated for 30 min to obtain a homogeneous mixture. Then, 0.2 mL of 6 mol / L acetic acid catalyst was added to the mixture. The Piezerx tube was placed in liquid nitrogen for freezing, and the mixture was evacuated and purged with nitrogen three times using a vacuum pump. The tube was then flame-sealed, cooled to 25°C, and placed in a 25°C oven for 7 days. After the reaction, the mixture was extracted with acetone for 12 h, and then vacuum-dried at 80°C for 12 h to obtain a reddish-brown powder, named TF-PA-COOH COF. Sample images of the material are shown below. Figure 3 As shown.

[0042] Example 3 Synthesis of TF-PA-COOH-COF

[0043] TF (46.86 mg, 0.12 mmol) and PA-COOH (27.39 mg, 0.18 mmol) were added to a Piezerx tube. 1 mL of trimethylbenzene and 1 mL of ethanol were added, and the mixture was ultrasonicated for 30 min to obtain a homogeneous mixture. Then, 0.2 mL of 3 mol / L acetic acid catalyst was added to the mixture. The Piezerx tube was placed in liquid nitrogen for freezing, and the mixture was evacuated and purged with nitrogen three times using a vacuum pump. The tube was then flame-sealed, cooled to 25°C, and placed in a 100°C oven for 5 days. After the reaction, the mixture was extracted with N,N-dimethylformamide for 12 h, and then vacuum-dried at 100°C for 20 h to obtain a reddish-brown powder, named TF-PA-COOH COF. Sample images of the material are shown below. Figure 4 As shown.

[0044] Comparative Example 1: Preparation of TF-PPD COF

[0045] The difference between this comparative example and Example 1 is that PA-COOH is replaced with PPD, while the other components and steps remain unchanged.

[0046] TF (15.62 mg, 0.04 mmol) and PPD (6.49 mg, 0.06 mmol) were added to a Pyrex tube, followed by the addition of 0.5 mL of o-dichlorobenzene and 0.5 mL of n-butanol. The mixture was then sonicated for 30 min to obtain a homogeneous mixture. 0.2 mL of 5 mol / L acetic acid catalyst was added to the mixture. The Pyrex tube was then frozen in liquid nitrogen, evacuated by a vacuum pump, and purged with nitrogen three times. The tube was then flame-sealed, cooled to 25 °C, and placed in a 120 °C oven for 3 days. After the reaction, the mixture was extracted with anhydrous tetrahydrofuran for 12 h, and then vacuum-dried at 120 °C for 24 h to obtain a yellow powder, which was named TF-PPD COF.

[0047] Comparative Example 2: Preparation of PTA-TAPA COF

[0048] The difference between this comparative example and Example 1 is that TF is replaced with TAPA and PA-COOH is replaced with PTA, while the other components and steps remain unchanged.

[0049] TAPA (13 mg, 0.026 mmol) and PTA (59.5 mg, 0.44 mmol) were added to a Pyrex tube, followed by the addition of 0.5 mL of o-dichlorobenzene and 0.5 mL of n-butanol. The mixture was then sonicated for 30 min to obtain a homogeneous mixture. 0.2 mL of 5 mol / L acetic acid catalyst was added to the mixture. The Pyrex tube was then frozen in liquid nitrogen, evacuated by a vacuum pump, and purged with nitrogen three times. The tube was then flame-sealed, cooled to 25 °C, and placed in a 120 °C oven for 3 days. After the reaction, the mixture was extracted with anhydrous tetrahydrofuran for 12 h, and then vacuum-dried at 120 °C for 24 h to obtain COF powder, which was named PTA-TAPA COF.

[0050] Comparative Example 3: Preparation of Tp-PA-COOH COF

[0051] The difference between this comparative example and Example 1 is that TF is replaced with Tp, while the other components and steps remain unchanged.

[0052] Tp (21 mg, 0.1 mmol) and PA-COOH (23 mg, 0.15 mmol) were added to a Piezerx tube, followed by the addition of 0.5 mL of o-dichlorobenzene and 0.5 mL of n-butanol. The mixture was then sonicated for 30 min to obtain a homogeneous mixture. 0.2 mL of 5 mol / L acetic acid catalyst was added to the mixture. The Piezerx tube was then frozen in liquid nitrogen, evacuated by a vacuum pump, and purged with nitrogen three times. The tube was then flame-sealed, cooled to 25 °C, and placed in a 120 °C oven for 3 days. After the reaction, the mixture was extracted with anhydrous tetrahydrofuran for 12 h, and then vacuum-dried at 120 °C for 24 h to obtain COF powder, which was named Tp-PA-COOH COF.

[0053] Comparative Example 4: Preparation of TF-DABA-COOH COF

[0054] The difference between this comparative example and Example 1 is that PA-COOH is replaced with DABA, while the other components and steps remain unchanged.

[0055] TF (15.62 mg, 0.04 mmol) and DABA (11.77 mg, 0.06 mmol) were added to a Pierrex tube, followed by the addition of 0.5 mL of o-dichlorobenzene and 0.5 mL of n-butanol. The mixture was then sonicated for 30 min to obtain a homogeneous mixture. 0.2 mL of 5 mol / L acetic acid catalyst was added to the mixture. The Pierrex tube was then frozen in liquid nitrogen, evacuated by a vacuum pump, and purged with nitrogen three times. The tube was then flame-sealed, cooled to 25 °C, and placed in a 120 °C oven for 3 days. After the reaction, the mixture was extracted with anhydrous tetrahydrofuran for 12 h, and then vacuum-dried at 120 °C for 24 h to obtain COF powder, named TF-DABA-COOH COF.

[0056] Experimental Example 1: Structural Characterization of TF-PA-COOH COF Material

[0057] To determine the structure of the TF-PA-COOH COF material prepared in Example 1, relevant tests were conducted.

[0058] Figure 5 This is the X-ray diffraction pattern of TF-PA-COOH COF. During testing, the dry, powdered COF sample was evenly loaded into the sample holder and flattened to ensure a smooth surface. The sample holder was then placed into the XRD instrument, and the parameters were set in the software: the scanning range was set to 2-30°, and the scanning speed was 10° / min. After the test, the data was processed and the positions and intensities of the characteristic diffraction peaks were analyzed. Figure 5 The material exhibits distinct characteristic diffraction peaks, indicating the successful synthesis of the COF material.

[0059] Figure 6This is the Fourier transform infrared (FTIR) spectrum of TF-PA-COOH COF. During testing, the dry COF powder sample is evenly spread on the crystal sample stage of the ATR accessory, ensuring close contact between the sample and the crystal surface. A pressure bar is used to apply uniform pressure to guarantee sufficient contact. The infrared spectrometer is then started, and the scanning parameters are set in the software (typically the scanning range is 4000-400 cm⁻¹). -1 First, background spectra were acquired, then the sample was placed and scanned. After testing, the spectra were processed using software to analyze the position and shape of characteristic absorption peaks, focusing on the characteristic peaks of functional groups such as imine bonds (C=N), carboxyl groups (COOH), aldehyde groups (CHO), and amino groups (NH). These peaks were compared with the raw material spectra (TF, PA-COOH) to verify the structure of the TF-PA-COOH COF material and the formation or transformation of functional groups. Figure 6 As can be seen, the amino and aldehyde peaks of TF-PA-COOH COF disappear, and the C=N bond (wavenumber 1621 cm⁻¹) is also visible. -1 The appearance of stretching vibration peaks proves the successful synthesis of TF-PA-COOH COF material.

[0060] Figure 7 This is a SEM image of TF-PA-COOH COF. The testing procedure was as follows: 1) A conductive tape with a length of 1 cm and a width of 0.5 cm was attached to the sample stage; 2) The protective film on the conductive tape was removed, and a small amount of powder was evenly applied to the conductive tape; 3) For non-magnetic powder samples, any loose powder samples were blown off with a syringe; 4) The sample was placed in a gold sputtering machine for 180 seconds for gold sputtering treatment; 5) The sample was observed on the machine. Figure 7 It can be seen that the TF-PA-COOH COF material is composed of stacked rod-shaped structures.

[0061] Experiment Example 2: Adsorption performance of TF-PA-COOH COF material for thorium under different pH conditions

[0062] The TF-PA-COOH COF material prepared in Example 1 was subjected to thorium adsorption performance experiments under different pH conditions at room temperature (25°C). A 100 ppm thorium-containing solution was used as the test solution. The pH of the test solution was adjusted to 1, 2, 3, 4, and 5 using nitric acid aqueous solution and sodium hydroxide aqueous solution, respectively. Then, 2 mg of the TF-PA-COOH COF material prepared in Example 1 was added to 6 mL of the pH-adjusted test solution for adsorption experiments. The adsorption time was 24 h, and ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) was used for testing. The thorium-containing solutions before and after adsorption were first diluted with 2% dilute nitric acid, and the samples after adsorption were ensured to be clear by centrifugation and filtration to prevent instrument clogging. Next, a set of thorium standard solutions was prepared using the dilution medium, and a standard curve was established using ICP-OES. Subsequently, the blank, pre-adsorption, and post-adsorption sample solutions were measured sequentially. The instrument automatically calculated the concentration based on the standard curve. The blank sample was a 2% dilute nitric acid solution. Finally, the concentrations C0 before adsorption and C2 after adsorption were calculated. e By combining the solution volume and the adsorbent mass, the adsorption capacity and removal rate can be calculated. The formulas for calculating the adsorption capacity and removal rate are as follows:

[0063] ;

[0064] ;

[0065] Where, q e This refers to the adsorption capacity, expressed in mg / g. -1 R represents the removal rate; C0 represents the initial concentration of thorium ions, in ppm; C e V represents the concentration of thorium ions after adsorption, in ppm; V represents the volume of the thorium solution, in mL; and m represents the mass of the TF-PA-COOH COF material, in mg.

[0066] Experimental results are as follows Figure 8 As shown, the TF-PA-COOH COF material does not adsorb at pH 1.0. In the pH range of 2.0-5.0, its adsorption capacity shows an increasing trend with increasing pH, and reaches adsorption equilibrium at pH 4.0.

[0067] Experiment Example 3: Adsorption isotherm experiment of thorium on COF material

[0068] As shown in Experiment 2, the TF-PA-COOH-COF material can reach adsorption equilibrium for thorium ions at a hydrogen ion concentration index of pH = 4.0. Therefore, this experiment was conducted under the conditions of pH = 4.0 and temperature 25℃, with a concentration gradient of 25 mg / L. -1 50mg L -1 75mg L -1100mg L -1 150mg L -1 200mg L -1 250mg L -1 300mg / L -1 350mg L -1 400mg L -1 500mg L -1 600mg L -1 700mg L -1 800mg L -1 and 1900mg L -1 A thorium-containing solution was used as the adsorption solution. Then, 2 mg of TF-PA-COOH COF material prepared in Example 1, 2 mg of TF-PPD COF material prepared in Comparative Example 1, 2 mg of PTA-TAPA COF material prepared in Comparative Example 2, 2 mg of Tp-PA-COOH COF material prepared in Comparative Example 3, and 2 mg of TF-DABA-COOH COF material prepared in Comparative Example 4 were added to 6 mL of adsorption solutions of different concentrations for adsorption isotherm experiments. The adsorption time was 24 h. The concentration of thorium ions before and after adsorption was determined using ICP-OES, and the adsorption capacity of each COF material was calculated. The adsorption capacity formula is the same as in Experiment 2. In adsorption isotherm experiments with pre-set concentration gradients, it is usually necessary to fit the experimental data using a classical adsorption model to quantitatively analyze the adsorption performance of the material. The most commonly used is the Irwin model. Langmuir model and Freundlich isotherm model.

[0069] Kyrie Irving The Langmuir model is based on the assumptions of a homogeneous adsorbent surface, adsorption as a monolayer, and no intermolecular interactions among adsorbed molecules. The maximum saturation adsorption capacity in the model's fitting results is a key parameter for assessing the adsorbent's capacity limit, and its linearized form also helps in calculating the adsorption equilibrium constant.

[0070] The Freundlich isotherm model is an empirical formula, better suited for describing adsorption on heterogeneous surfaces. Its fitting parameters reflect the intensity of adsorption and the non-uniformity of the adsorbent surface.

[0071] Therefore, after the experiment was completed, the equilibrium adsorption data at different concentrations were respectively analyzed using Irwin's method. Fitting the Langmuir model and the Freundlich isotherm model allows for a more in-depth assessment of the upper limit of the adsorption capacity of TF-PA-COOH COF materials for thorium ions.

[0072] Experimental results are as follows Figure 9As shown in Table 1, under pH=4.0 conditions, the maximum adsorption capacity of thorium by the TF-PA-COOH COF material prepared in Example 1 was 2495 mg g. -1 It is superior to the COF materials prepared in Comparative Examples 1-4.

[0073] Table 1 Comparison of Maximum Adsorption Capacity

[0074]

[0075] Experiment Example 4: Multi-component adsorption experiment of TF-PA-COOH COF material

[0076] Multicomponent adsorption selectivity experiments were conducted at pH 4.0. Different competing ions, Th(IV), U(VI), Rb(I), La(III), Pr(III), Sm(III), Gd(III), and Lu(III), were coexisted in a mixed solution. The concentration of both competing ions and thorium was 100 ppm. Then, 2 mg of the TF-PA-COOH COF material prepared in Example 1 was added to 6 mL of the mixed solution for adsorption experiments. The adsorption time was 24 h. The concentrations of each ion before and after adsorption were determined by ICP-OES. The formulas for calculating the partition coefficient and separation factor are as follows:

[0077] ;

[0078] Where C0 is the initial concentration of ions before adsorption, in ppm; C e The concentration of ions after adsorption is expressed in ppm; m is the mass of TF-PA-COOH COF material used, expressed in mg; V is the volume of the adsorption solution, expressed in mL. The partition coefficient for thorium ions is expressed in mL / g. -1 ; The partition coefficient for competing metal ions, expressed in mL / g. -1 .

[0079] The results are as follows Figure 10 As shown, under conditions of pH = 4.0 and ion concentrations of 100 ppm, the TF-PA-COOH COF prepared in Example 1 showed almost no adsorption or extremely low adsorption for competing ions such as U(VI), Rb(I), La(III), Pr(III), Sm(III), Gd(III), and Lu(III); the partition coefficient of TF-PA-COOH COF material for thorium ( The value reached 7.2 × 10⁻⁶. 4 mL g -1 The allocation coefficient for uranium ( ) is 338mL g -1 The allocation coefficient for samarium ( ) is 1 mL g -1 The allocation coefficient for gadolinium ( ) is 9mL g -1 The allocation coefficient for lanthanum ( ) is 9mL g -1 The distribution coefficient for rubidium ( ) is 12mL g -1 The distribution coefficient for lutetium ( ) is 34mL g -1 It does not adsorb praseodymium. The separation factor for competing ions reaches 214~7.2×10⁻⁶. 4 Among them, the thorium / uranium separation factor SF Th / U The value is 214, and the thorium / samarium separation factor is 7.2 × 10⁻⁶. 4 The thorium / gadolinium separation factor is 8.0 × 10⁻⁶. 3 The thorium / lanthanum separation factor is 8.0 × 10⁻⁶. 3 The thorium / rubidium separation factor is 6.0 × 10⁻⁶. 3 The thorium / lutetium separation factor is 2.1 × 10⁻⁶. 3 This indicates that the TF-PA-COOH COF material exhibits excellent adsorption selectivity for thorium under the presence of multiple competing ions, and can achieve selective adsorption and separation of thorium.

[0080] This demonstrates that TF-PA-COOH COF has the following advantages in adsorbing thorium:

[0081] (1) Compared with TF-PPD COF (Comparative Example 1) which contains only imine bonds, the carboxyl group (-COOH) introduced in TF-PA-COOH COF is a Lewis base, which has a stronger chelating ability for thorium ions. At the same time, the C=O oxygen atom on the carboxyl group is also an excellent hydrogen bond acceptor, which significantly improves the chemical adsorption activity and binding site density of the material.

[0082] (2) Compared with the three-dimensional PTA-TAPA COF (Comparative Example 2) which does not have specific interlayer interaction, TF-PA-COOH COF creates a cavity in the interlayer that is suitable for hydrated thorium ions through the reverse stacking of carboxyl groups. Through the synergistic adsorption mechanism of "strong chemical coordination + interlayer hydrogen bonding", it forms a multi-site and multi-step adsorption enhancement effect.

[0083] (3) Compared with the ketone structure Tp-PA-COOH COF (Comparative Example 3), its advantage lies in the specific trialdehyde monomer (TF) and connection mode, which is the key to achieving ideal interlayer spacing and forming effective reverse stacking. This directly determines its high adsorption capacity and high separation selectivity.

[0084] (4) Compared with TF-DABA COF (Comparative Example 4) which contains carboxyl groups on both sides but does not form reverse stacking, its advantage lies in the reverse arrangement of carboxyl groups on one side in space. This is the core structure that synergistically leverages interlayer hydrogen bonds and intralayer coordination to achieve a leap in performance.

[0085] Comprehensive comparisons show that TF-PA-COOH COF materials exhibit significant advantages in the selective adsorption of thorium due to their unique "carboxyl functionalization" and "synergistic effect of hydrogen bonding and chemical coordination".

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A reverse-stacked TF-PA-COOH COF material characterized in that, The structure of the reverse-stacked TF-PA-COOH COF material is shown as formula (I): 。 2. The method of claim 1, wherein the reverse-stacked TF-PA-COOH COF material is prepared by the steps of: The method comprises the following steps: An aldehyde monomer, an amino monomer and an organic solvent are added into a reaction tube, and the mixture is ultrasonically treated; a catalyst is added into the mixture, the mixture is frozen in liquid nitrogen, the tube is vacuumized and filled with nitrogen, the tube is flame-sealed, and the tube is cooled to 20-25 DEG C and then heated for crystallization; a solid is collected, washed, filtered and vacuum-dried to obtain the reverse-stacked TF-PA-COOH COF material.

3. The production method according to claim 2, wherein The aldehyde monomer is 1,3,5-tris(4-formylphenyl)benzene, and the amino monomer is 2,5-diaminobenzoic acid.

4. The production method according to claim 2, wherein The organic solvent is selected from any one of the following: a mixed solution of o-dichlorobenzene and n-butanol in a volume ratio of 1: (1-3), a mixed solution of mesitylene and ethanol in a volume ratio of 1: (1-10), and a mixed solution of mesitylene and 1,4-dioxane in a volume ratio of 1: (1-10).

5. The production method according to claim 2, wherein The molar ratio of the aldehyde monomer to the amino monomer in the mixture is 2 mmol: (1-3) mmol, and the volume of the organic solvent to the sum of the mass of the aldehyde monomer and the amino monomer is 1 mL: (24.8-37.1) mg.

6. The production method according to claim 2, wherein The catalyst is an acetic acid solution with a concentration of 3-6 mol / L, and the molar amount of the aldehyde monomer to the volume of the catalyst is 1 mmol: 5 mL.

7. The production method according to claim 2, wherein The ultrasonic treatment time is 10-30 min, the heating crystallization temperature is 25-120 DEG C, and the reaction time is 3-7 days; the vacuum drying temperature is 80-120 DEG C, and the drying time is 12-24 h.

8. The production method according to claim 2, wherein The solid washing solvent is at least one of anhydrous tetrahydrofuran, acetone and N,N-dimethylformamide.

9. The reverse-stacked TF-PA-COOH COF material of claim 1 or the reverse-stacked TF-PA-COOH COF material prepared by the preparation method of any one of claims 2-8 is applied to thorium ion selective adsorption and separation.

10. Use according to claim 9, wherein The solution environment pH of the thorium ion selective adsorption and separation is 2.0-5.0.

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