Janus covalent organic framework membranes with synergistically enhanced coordination and methods of making and using the same

Abstract

This invention belongs to the field of covalent organic framework membrane material synthesis, specifically involving a synergistically coordinated Janus covalent organic framework membrane, its preparation method, and its application. To address the problems of existing covalent organic framework membranes, such as the inability to continuously adjust pore size, defects in crystallinity and pore structure, which make it difficult to achieve ion-selective separation directly using size sieving, this invention provides a synergistically coordinated Janus covalent organic framework membrane (2D Janus COFs membrane). The structural formula of the above-mentioned synergistically coordinated Janus covalent organic framework membrane is shown in Formula I. This invention also provides the application of the above-mentioned synergistically coordinated Janus covalent organic framework membrane in the preparation of Sr / Y separation materials. The COF membrane provided by this invention has more multifunctional sites, enhancing its coordination ability for Y(III), promoting the effective separation of Sr and Y, and providing a new approach for the development of highly efficient Sr / Y separation porous materials.

Description

Technical Field

[0001] This invention belongs to the field of covalent organic framework membrane material synthesis, specifically relating to synergistic coordination-enhanced Janus covalent organic framework membranes, their preparation methods, and applications. Background Technology

[0002] 90 Y has a suitable half-life (T) 1 / 2 =64.1h), high-energy β rays (E max =2.28MeV) and stable decay products, based on 90 Radiopharmaceuticals based on Y have been widely used in the treatment of cancer by radiolabeling different target molecules and in radiotherapy for synovectomy. 90 The main preparation method of Y is to... 90 Sr decays 90 Y. However. 90 Sr is a highly toxic element with a strong affinity for bone and a long half-life. According to the United States Pharmacopeia (USP) guidelines, when injecting... 90 In solution Y 90 Sr / 90 The proportion of Y should not exceed 2.0 × 10 -5 Therefore, efficient separation of Sr and Y is required. Currently, commonly used Sr / Y separation methods include solid-phase extraction, ion exchange, and solvent extraction. However, based on existing technologies and materials, these methods all have their own drawbacks. For example, liquid-liquid extraction suffers from problems such as easy emulsification, easy loss of extractant, and a large amount of secondary waste; ion exchange suffers from low adsorption capacity, low selectivity, and high cost of ion exchange resins. Therefore, it is necessary to develop new separation materials and technologies.

[0003] Membrane separation technology combines the functions of separation, purification, and concentration, and features simple separation processes, no chemical changes, no phase changes, low energy consumption, strong process adaptability, and good reusability, making it a promising technology for ion separation. To date, commercially available membrane materials are mostly polymers, such as polytetrafluoroethylene (PTFE) membranes, polyvinylidene fluoride (PVDF) membranes, cellulose acetate membranes, and polyimide membranes. These polymers offer advantages such as stability, ease of processing and molding, and mature preparation technologies. However, limitations imposed by the intrinsic structure of these materials result in problems such as large pore size, uneven pore distribution, difficulty in controlling pore size, and challenges in functionalization. These limitations make it difficult to balance permeability and selectivity, affecting membrane separation efficiency. Therefore, the development of membrane materials specifically designed for ion selective separation is urgently needed.

[0004] Two-dimensional covalent organic frameworks (COFs) are novel porous crystalline organic materials formed by small organic molecules linked by covalent bonds. Benefiting from their abundant monomer sources, flexible and reversible linkages, and well-defined reaction pathways, COFs possess highly ordered periodic structures, easily tunable pore sizes, and flexibly designed active sites. They also offer advantages such as the ability to remove specific ions by modifying the pore environment, making COFs an effective material for manufacturing highly efficient and selective sieving membranes. Size sieving is a crucial separation mechanism for current COF membranes. For example, Banerjee et al. prepared a series of COF membranes with pore sizes ranging from 1.4 to 2.6 nm using a water-organic solvent interface method. These membranes exhibited good solvent permeation rates, and dye blocking experiments showed that COF membranes had a significant sieving effect on dye molecules of different sizes. [1] However, the hydrated size of most nuclide ions is less than 1 nm, and the difference between different ion sizes is very small. On the other hand, most COF membranes synthesized based on current monomer combinations and preparation methods have pore sizes greater than 1 nm. Furthermore, due to limitations in monomer size and symmetry, the pore size of COF membranes cannot be continuously adjusted, making it difficult to achieve ion-selective separation directly using size sieving.

[0005] To improve the selective separation of target ions by COF membranes, researchers often employ post-functionalization modification methods, grafting molecules rich in active functional groups onto the surface of COF membrane materials. For example, Cao Li et al. grew ethylene-functionalized COF membranes on commercial polyacrylonitrile membrane substrates via a three-component interfacial polymerization reaction, and then modified the pores of the COF membranes with cysteine ​​via a click reaction of ethylene and thiol groups, preparing amino acid-functionalized COF membrane materials. Before the click reaction, the COF membranes were sensitive to Na+. + and K + The osmotic rates were 9.1 and 16.2 mmol m, respectively. -2 h -1 K + / Na + The selectivity was 1.8. After the click reaction, Na... + and K + The permeation rates increased by 1.5 times and 1.2 times, respectively. Since cysteine ​​contains pH-sensitive carboxyl and amino groups, and its isoelectric point is 5.02, the authors also studied the ion diffusion characteristics under two representative pH conditions: pH = 3.8 and pH = 8.9. At pH = 3.8, the COFs membrane showed increased permeation rates for Na+. + and K + The osmosis rates were 12.6 and 21.4 mmol h, respectively. -1 m -2 K+ / Na + The selectivity was 1.7. However, when the solution pH increased to 8.9, the COFs membrane showed increased selectivity for Na+. + and K + The osmosis rates were 73.7 mmol / h. -1 m -2 and 27.3 mmol h -1 m -2 Na + / K + With a selectivity of 2.7, Na is thus achieved. + / K + Selective and controllable adjustment provides a powerful platform for the separation of monovalent cations. [2] However, post-functionalization modification methods not only struggle to guarantee a high modification rate, but also... [3-5] Furthermore, functionalization of COF membrane materials can lead to the loss of their original good crystallinity, resulting in an increase in amorphous states and pore blockage. This is the main problem encountered by most post-modified COF membrane materials. Summary of the Invention

[0006] To address the problems of existing covalent organic framework membranes, such as the inability to continuously adjust pore size, defects in crystallinity and pore structure, which make it difficult to achieve ion-selective separation directly using size sieving, this invention provides a synergistically coordinated Janus covalent organic framework membrane (2D Janus COFs membrane). The structural formula of the above-mentioned synergistically coordinated Janus covalent organic framework membrane is shown in Formula I:

[0007]

[0008] Where X is C or N, and R1 to R4 are independently -H or -OH.

[0009] Preferably, R1 to R4 are independently -H or -OH, and not simultaneously -H or -OH.

[0010] The structure of the aforementioned co-coordination-enhanced Janus covalent organic framework membrane is as follows:

[0011]

[0012] This invention also provides a method for preparing the above-mentioned synergistic coordination-enhanced Janus covalent organic framework membrane (see schematic diagram). Figure 1 The method for preparing the synergistically coordinated enhanced Janus covalent organic framework membrane is a synthesis using the acetic acid buffer interlayer interface method, and the reaction formula is as follows:

[0013]

[0014] The specific steps of the above-mentioned method for preparing the synergistically enhanced Janus covalent organic framework membrane include:

[0015] a. Dissolve the aldehyde monomer in dichloromethane as the lower organic phase layer, and then slowly add acetic acid as the intermediate buffer aqueous phase layer;

[0016] b. Dissolve the amine monomer in DMF (N,N-dimethylformamide) solution, and then slowly add it dropwise onto the intermediate buffer aqueous phase layer as the upper organic phase layer;

[0017] c. The above-mentioned layered mixture was allowed to stand at room temperature for 3 days to react, and then a solid product was obtained at the interface. The product was washed with water and ethanol in sequence to obtain a coordinatingly enhanced Janus covalent organic framework membrane.

[0018] In the above-mentioned method for preparing the synergistically coordinated enhanced Janus covalent organic framework membrane, the mass-volume ratio of the aldehyde monomer to dichloromethane in step a is 20 mg: 60 mL to 60 mg: 100 mL.

[0019] In the above method for preparing the synergistically enhanced Janus covalent organic framework membrane, the acetic acid in step a is 6M.

[0020] In the above-mentioned method for preparing the synergistically enhanced Janus covalent organic framework membrane, the mass-volume ratio of the amine monomer to DMF in step b is 40 mg:30 mL to 80 mg:70 mL.

[0021] In the above-mentioned method for preparing the synergistically coordinated enhanced Janus covalent organic framework membrane, the molar ratio of the aldehyde monomer and the amine monomer in steps a and b is 1:1.1 to 1:1.5.

[0022] This invention also provides the application of the above-mentioned synergistic coordination-enhanced Janus covalent organic framework membrane in the preparation of Sr / Y separation materials.

[0023] The Janus covalent organic framework membrane with enhanced synergistic coordination provided by this invention is synthesized using an acetic acid buffer interlayer interface method. This invention obtains two types of COF membranes by positioning hydroxyl groups at specific positions: one with ortho-hydroxyl groups, which can synergistically coordinate with ions; and the other with para-hydroxyl groups, which cannot synergistically coordinate with ions. This invention investigates the effect of the two chelating group configurations of COF membranes on Sr / Y separation performance. The results show that, with the same number of hydroxyl groups, the ortho-hydroxyl COF membrane, due to its additional binding sites, is more likely to complex with Y(III) compared to the para-hydroxyl COF membrane. In the Sr / Y separation system, the ortho-hydroxyl COF membrane with synergistic coordination ability exhibits a selectivity of up to 99.7% for Sr(II), and this selectivity remains above 95% after five repeated experiments; while the selectivity of the para-hydroxyl COF membrane for Sr(II) is only 66.4%. This indicates that COF membrane materials with ortho-hydroxyl groups have more functional sites that coordinate with Y(Ⅲ), thereby achieving efficient Sr / Y separation. Attached Figure Description

[0024] Figure 1 Schematic diagram of the synthesis of four types of 2D Janus COFs membranes.

[0025] Figure 2 (a) to (d) are the infrared spectra of o-Tb COF, p-Tb COF, o-Tt COF and p-Tt COF films and monomers, respectively; (e) to (h) are the PXRD patterns and MS simulation images of o-Tb COF, p-Tb COF, o-Tt COF and p-Tt COF films, respectively.

[0026] Figure 3 (a~d) show the nitrogen adsorption-desorption curves, pore size distribution, MS simulated pore size, and SEM images and magnified views of o-Tb COF, p-Tb COF, o-Tt COF, and p-Tt COF membranes, respectively.

[0027] Figure 4 (a~d) represent the PXRD of o-Tb COF, p-Tb COF, o-Tt COF and p-Tt COF membranes at different acidities, respectively, and (e~h) represent the FTIR of o-Tb COF, p-Tb COF, o-Tt COF and p-Tt COF membranes at different acidities, respectively.

[0028] Figure 5(ab) shows the FT-IR spectra of o-Tb COF and p-Tb COF films before and after irradiation with 100-300 kGy β rays, and (cd) shows the FT-IR spectra of o-Tb COF and p-Tb COF films before and after irradiation with 100-300 kGy γ rays.

[0029] Figure 6 (a-d) shows the water flux of the COF membrane on the side closer to the DMF solution and the side closer to the CH2Cl2 solution, respectively. (e) is a SEM image of the o-Tb COF membrane on the side closer to the DMF solution, and (f) is a SEM image of the o-Tb COF membrane on the side closer to the CH2Cl2 solution.

[0030] Figure 7 (a-c) are bar charts showing the separation effect of COF membrane material at different feed concentrations (concentrations are 0.1 mmol / L, respectively). -1 0.25 mmol / L -1 and 0.5 mmol L -1 (de) is a graph showing the long-term concentration changes of o-Tb COF and p-Tb COF membranes, and (f) is a graph showing the repeated performance of o-Tb COF membrane.

[0031] Figure 8 The images show SEM images of o-Tb COF, p-Tb COF, o-Tt COF, and p-Tt COF membranes in their original, separated, and eluted states, respectively.

[0032] Figure 9 The images show the PXRD patterns of o-Tb COF, p-Tb COF, o-Tt COF, and p-Tt COF membranes in their original, separated, and eluted states, respectively.

[0033] Figure 10 EDX images of o-Tb COF membrane before (a) and after (b) elution.

[0034] Figure 11 Schematic diagram of the binding functional sites for Sr / Y separation using four types of COF membranes.

[0035] Figure 12 (a~c) are the full spectrum, O spectrum and N spectrum of XPS of o-Tb COF membrane material, respectively, and (d~f) are the full spectrum, O spectrum and N spectrum of XPS of p-Tb COF membrane material, respectively (the sample after COF adsorbs Y is named COF@Y).

[0036] Figure 13 Binding energy and electrostatic potential (ESP) of yttrium nitrate with two COF configurations (green represents C; white represents H; red represents O; purple represents N; yellow represents Y). Detailed Implementation

[0037] The preparation method of synergistically coordinated enhanced Janus covalent organic framework membranes includes the following specific steps:

[0038] a. The aldehyde monomer is dissolved in dichloromethane as the lower organic phase layer, and then 6M acetic acid is slowly added dropwise as the intermediate buffer aqueous phase layer; the mass-to-volume ratio of the aldehyde monomer to dichloromethane is 20mg:60mL to 60mg:100mL.

[0039] b. Dissolve the amine monomer in a DMF (N,N-dimethylformamide) solution, and then slowly add it dropwise onto the intermediate buffer aqueous phase layer as the upper organic phase layer; the mass-volume ratio of the amine monomer to DMF is 40mg:30mL to 80mg:70mL.

[0040] c. The above-mentioned layered mixture was allowed to stand at room temperature for 3 days to react, and then a solid product was obtained at the interface. The product was washed with water and ethanol in sequence to obtain a coordinatingly enhanced Janus covalent organic framework membrane.

[0041] In the above-mentioned method for preparing the synergistically coordinated enhanced Janus covalent organic framework membrane, the molar ratio of the aldehyde monomer and the amine monomer in steps a and b is 1:1.1 to 1:1.5.

[0042] Tris(4-aminophenyl)benzene (Tb), 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (Tt), 2,5-dihydroxy-terephthalaldehyde (p-CHO), and 2,3-dihydroxy-o-phthalaldehyde (o-CHO) were all purchased from Shanghai Kaiyulin Pharmaceutical Technology Co., Ltd. Yttrium nitrate hexahydrate (Y(NO3)3·6H2O) and strontium nitrate (Sr(NO3)2) were purchased from Anaiji (Shanghai) Pharmaceutical Chemical Co., Ltd. N,N-dimethylformamide (DMF), dichloromethane, and glacial acetic acid were all purchased from Chengdu Kelon Chemical Reagent Co., Ltd., China. All reagents and solvents used in this study were of a purity that required no further purification before use.

[0043] Example 1: Synthesis of Janus covalent organic framework membranes with different co-coordination enhancements:

[0044]

[0045] First, o-CHO (44.08 mg, 0.26 mmol) was dissolved in 80 mL of dichloromethane as the lower organic phase. Then, 40 mL of 6M acetic acid was slowly added dropwise as an intermediate buffer aqueous phase. Finally, Tb (61.15 mg, 0.174 mmol) was dissolved in 50 mL of DMF solution as the upper organic phase. The beaker was allowed to stand at room temperature for 3 days. A solid product was then obtained at the interface, which was washed successively with water and ethanol to obtain the o-Tb COF membrane.

[0046] The p-Tb COF membrane was prepared by the above method using p-CHO (44.08 mg, 0.26 mmol) and Tb (61.15 mg, 0.174 mmol) monomers.

[0047] The o-Tt COF membrane was prepared by the above method using o-CHO (44.08 mg, 0.26 mmol) and Tt (61.67 mg, 0.174 mmol) monomers.

[0048] The p-Tt COF membrane was prepared by the above method using p-CHO (44.08 mg, 0.26 mmol) and Tt (61.67 mg, 0.174 mmol) monomers.

[0049] Example 2 Characterization of Janus covalent organic framework membranes with enhanced synergistic coordination

[0050] The four COF membranes prepared in Example 1 of this invention are named o-Tb COF, p-Tb COF, o-Tt COF and p-Tt COF, respectively.

[0051] 1) The formation of the COF film was characterized by Fourier transform infrared (FTIR) spectroscopy. The FTIR spectrum shows that ( Figure 2 a~d), C=O(1653cm) in monomer o-CHO -1 Characteristic absorption peaks and the -NH2 of monomer Tb (3210~3466cm) -1 The characteristic peak of 1620 cm⁻¹ disappeared. -1 The appearance of new C=N stretching vibration peaks on the left and right provides evidence of a successful condensation reaction between the aldehyde and amine. Similarly, C=O (~1653 cm⁻¹) can be observed in the infrared spectra of p-Tb COF, o-Tt COF, and p-Tt COF. -1 ) and -NH2 (3200-3500cm -1 The disappearance of the characteristic peak and the appearance of the C=N characteristic peak indicate that these three COF membranes also successfully underwent the aldehyde-amine condensation reaction.

[0052] Next, based on powder X-ray diffraction (PXRD) data, the layer stacking pattern of these COFs was simulated using Materials Studio (MS). For example... Figure 2As shown in Figure e, the XRD diffraction peak positions of o-Tb COF agree well with the diffraction peak positions of the AA stacking configuration simulated by MS. The diffraction peaks at 2.8°, 4.7°, 5.5°, 7.5°, and 9.9° of o-Tb COF correspond to the (100), (110), (200), (120), and (220) crystal planes. Similarly, the XRD spectra of p-Tb COF, o-Tt COF, and p-Tt COF also show that the XRD diffraction peak positions of the COFs agree well with the diffraction peaks of the AA stacking configuration obtained by MS simulation. Figure 2 f~h). Pawley refinement of the experimental PXRD data yielded good consistency factors (Rwp = 2.79% and Rp = 2.08% for o-Tb COF; Rwp = 3.39% and Rp = 2.61% for p-Tb COF; Rwp = 3.05% and Rp = 5.33% for o-Tt COF; Rwp = 3.13% and Rp = 2.18% for p-Tt COF).

[0053] 2) Generally speaking, the pore size will vary depending on the stacking method of the materials. In order to further determine the stacking method of COFs materials, we performed N2 adsorption-desorption characterization on four COFs materials.

[0054] The results are as follows Figure 3 As shown, the adsorption isotherm of o-Tb COF follows a typical type IV adsorption isotherm, reflecting that the pore distribution of o-TbCOF is mesoporous. Calculations using the nonlocal density functional method yield an average pore size of 3.0 nm for o-Tb COF, which matches the pore size of 3.3 nm simulated by MS for AA stacks, thus confirming that o-Tb COF is indeed AA-stacked. Similarly, the measured pore sizes of the other three COFs also match the simulated pore sizes. Furthermore, calculations based on the N2 adsorption-desorption isotherm show that the specific surface areas of the four COF materials—o-Tb COF, p-Tb COF, o-Tt COF, and p-Tt COF—are 184 m². 2 g -1 356m 2 g -1 878m 2 g -1 and 1253m 2 g -1 We found that the COF material with triazine centers had a significantly larger specific surface area than the COF material with benzene centers. This is likely due to the better planarity of the amine monomers at the triazine centers, resulting in stronger π-π stacking interactions between the COF layers, higher crystallinity, and a fixed porosity structure, thus leading to a larger specific surface area. Furthermore, scanning electron microscopy (SEM) images showed… Figure 3 (a and 3b) The microstructures of o-Tb COF and p-Tb COF (centered on the benzene ring) exhibit smooth planar structures, while o-Tt COF and p-Tt COF (centered on the triazine ring) show a ribbon-like morphology. Figure 3 (c and 3d). This difference stems from the influence of hydrogen bonds on structural features: the amine monomer at the center of the triazine ring makes the benzene ring almost in the same plane, resulting in strong interlayer π-π stacking and a high PXRD intensity ratio, which promotes growth along the Z-axis. In contrast, the COF film at the center of the benzene ring has weaker interlayer interactions due to the non-plane arrangement of the benzene ring, which inhibits Z-axis growth and ultimately forms dense spherical crystals.

[0055] 3) Physical and chemical stability

[0056] The physicochemical stability of membranes is one of the important indicators to ensure their effective application in real-world environments. The thermal stability, acid stability, and radiation stability of COF membranes were tested.

[0057] Thermogravimetric analysis (TGA) was used to determine the thermal stability of COF films in a N2 atmosphere. Thermogravimetric analysis results showed that weight loss below 100℃ was due to water evaporation, possibly related to the hydrophilicity of hydroxyl groups. Slight weight loss (approximately 10%) between 100 and 400℃ was likely due to the decomposition of some small molecules in the material. At 500℃, the mass percentages of o-TbCOF, p-Tb COF, o-Tt COF, and p-Tt COF films remained at 66.9%, 81.5%, 76.7%, and 77.6%, respectively. These results indicate that all four membrane materials possess excellent thermal stability.

[0058] The acid stability of COF membranes was assessed by immersing four membrane materials in nitric acid solutions at pH 3, pH 2, and pH 1 for 72 hours, respectively. After immersion, the samples were filtered, washed with water, and vacuum dried before PXRD and FTIR tests.

[0059] As can be seen from the PXRD spectra, the positions of the characteristic peaks of the four materials did not change significantly before and after immersion, and the positions and intensities of the characteristic peaks in the FTIR spectra of the four materials did not change significantly before and after immersion, indicating that they have good acid stability. Figure 4 ).

[0060] This invention tested the radiation stability of membrane materials with ortho-hydroxyl and para-hydroxyl configurations (taking o-Tb COF and p-Tb COF membranes as examples), by comparing their FT-IR spectra before and after irradiation with 100–300 kGy β and γ rays. Figure 5The radiation stability of these materials was evaluated. The test results showed that the position and intensity of the characteristic peaks in the FTIR spectra of the ortho-hydroxyl COF membrane material did not change significantly before and after β and γ ray irradiation, indicating that the membrane material has good radiation stability and can withstand β and γ ray irradiation of 300 kGy.

[0061] 4) Water flux

[0062] Because the different affinities for water on both sides of the o-Tb COF membrane were found during the experiment, this invention studies the water flux of the o-TbCOF membrane.

[0063] The results showed that the water flux of the o-Tb COF membrane was 12.45 L / h on the side closer to the DMF solution. -1 m -2 The water flux on the side closer to the CH2Cl2 solution is 4.16 L / h. -1 m -2 This is likely because, in the initial stage of o-Tb COF film growth, amine monomers in DMF react with aldehyde monomers through an acetic acid layer, forming a dense COF film at the acetic acid-dichloromethane interface. After COF film formation, the diffusion of amine monomers into the aldehyde solution is significantly hindered due to the relatively larger particle size of the amine monomers compared to the pore size of the COF. Furthermore, amine monomers can react with acetic acid to form salts, further hindering their diffusion into the aldehyde solution. However, aldehyde monomers diffuse more easily into the amine solution because their particle size is relatively small and unaffected by acetic acid. Under the catalysis of acetic acid, amine monomers in the amine solution react with aldehyde monomers to generate COF nanoparticles. Under gravity, these COF nanoparticles settle onto the initially grown COF film and gradually grow into another COF film. Figure 6 As shown, the side of the COF membrane closest to the DMF solution is porous, while the side closest to the CH2Cl2 solution is dense.

[0064] Example 3 Separation Experiment

[0065] The abundant N and O active sites in COF membranes provide a potential environment for the separation of target ions. We propose utilizing the rigid framework of COF to precisely position functional groups at specific locations, such as the two adjacent hydroxyl groups in o-Tb COF and o-Tt COF, which can additionally increase the binding functional sites, thereby enhancing the cooperative coordination ability of the COF membrane for target ions. To verify this idea, we conducted static diffusion experiments on four COF membranes with ortho- and para-hydroxyl configurations.

[0066] 1) Preparation of the solution: Weigh Y(NO3)3·6H2O (10.6 mg, 0.05 mmol) and Sr(NO3)2 (19.2 mg, 0.05 mmol) into the same beaker, then add 500 mL of deionized water with pH = 4.5, and stir to mix thoroughly to obtain an initial concentration of 0.1 mmol / L. -1 A metal ion solution can be prepared similarly. A concentration of 0.25 mmol / L can also be prepared. -1 and 0.5 mmol L -1 The concentration of metal ions in the solution.

[0067] 2) Static diffusion experiment: To investigate the transport characteristics of Sr / Y in COF membrane nanochannels, a static diffusion experiment was conducted using a U-shaped filter. A metal ion solution was placed as the feed solution on one side of the U-shaped filter, and deionized water was used as the permeate on the other side. The permeation rate of the metal ions was evaluated by measuring the metal ion concentration on the permeate side.

[0068] This invention uses an initial concentration of 0.1 mmol / L. -1 A mixed ionic solution of SrNO3 (strontium nitrate) and YNO3 (yttrium nitrate) was used as the feed solution. 125 mL of this feed solution (pH 4.5) was added to the feed side, and deionized water of equal pH and volume was added to the permeate side. Both the feed solution and the permeate were stirred with a magnetic stirrer to avoid concentration-diffusion polarization. To monitor ion permeation, 5 mL of the permeate was taken at fixed intervals, and the ion concentration was determined using ICP-OES. Simultaneously, 5 mL of the feed solution was taken to balance the pressure. The separation efficiency of the COF membrane material for strontium and yttrium was expressed as permeation rate (mmol / h). -1 m -2 The selectivity (%) was analyzed and calculated. To evaluate the recycling performance of the four membrane materials, the COF membrane was eluted after the static diffusion experiment by adding an aqueous solution of disodium ethylenediaminetetraacetic acid (EDTA) to one side of the U-shaped apparatus and allowing it to stand at room temperature for 24 hours. After washing the residual EDTA with deionized water, the static diffusion experiment was performed again.

[0069] The results are as follows Figure 7 As shown in Figure a, COF membranes with ortho-hydroxyl configurations (o-Tb COF and o-Tt COF) exhibit excellent coordination ability for Y(III) due to the presence of additional binding active functional sites in their structure. During separation, the selectivity for Sr(II) is as high as 98.4% and 94.1%, respectively, with permeabilities of 0.020 and 0.080 mmol / L. -1 m -2However, COF membranes with the para-hydroxyl configuration (p-Tb COF and p-Tt COF) lack additional functional active sites, resulting in selectivity for Sr of only 66.3% and 77.6%, respectively, with permeabilities of 0.068 and 0.103 mmol / L. -1 m -2 We also conducted static diffusion experiments by increasing the ion concentration of the feed solution, and the results are as follows: Figure 7 As shown in b and 7c, the permeability of Sr(II) increases with increasing feed concentration. Notably, when the initial concentration of the Sr / Y mixed ion solution (feed solution) increases to 0.25 and 0.5 mmol / L... -1 At that time, the o-TbCOF membrane still exhibited selectivity for Sr(II) as high as 99% and 99.8%, with permeabilities reaching 0.175 and 0.208 mmol / L. -1 m -2 The selectivity of p-Tb COF membranes for Sr(II) was only 64.2% and 63.9%, respectively, with permeabilities of 0.216 and 0.606 mmol / L. -1 m -2 This further verifies the view that the COF membrane with the ortho-hydroxyl configuration has excellent coordination ability for Y(Ⅲ) due to its structure.

[0070] Secondly, use 0.25 mmol L -1 A mixed ionic solution of strontium nitrate and yttrium nitrate was used to investigate the effect of time on static diffusion experiments, with the diffusion time extended to 144 hours. The results are as follows: Figure 7 d. At the start of the diffusion experiment, the ortho-hydroxyl-configured o-TbCOF membrane exhibited a strong coordination ability for Y(III), effectively blocking most of Y(III). This resulted in a Sr(II) selectivity of 99% in the first 24 hours. Subsequently, when the coordination of the o-Tb COF membrane for Y(III) reached saturation, Y(III) began to gradually permeate through the COF membrane. The enhanced coordination of the o-Tb COF membrane for Y(III) in the first 24 hours improved the Sr / Y separation effect, ensuring that the selectivity of the o-Tb COF membrane for Sr(II) remained above 70% even after 144 hours. However, as... Figure 7 As shown in e, the selectivity for Sr in the p-TbCOF membrane with the hydroxyl configuration is 66.8% in the first 24 hours.

[0071] Membrane reusability: such as Figure 7 As shown in f, in five repeated static diffusion experiments, the permeability of the two different COF membrane configurations to Sr / Y ions and their selectivity for Sr(II) did not change significantly. SEM images show ( Figure 8 The morphology of the COF membrane did not change significantly before and after separation, and its PXRD pattern ( Figure 9The results showed that the COF film maintained a good crystal structure, indicating its good mechanical stability during the experiment. Furthermore, the EDX electron images (…) Figure 10 The total distribution spectrum shows the disappearance of yttrium, indicating successful desorption of yttrium ions. The eluted COF membrane material can be used for the next separation cycle. Finally, we conducted a static diffusion experiment using the γ-ray irradiated o-Tb COF membrane. The selectivity of the o-Tb COF membrane for Sr(II) remained at 91.1%, indicating that the selectivity of the o-Tb COF membrane for Sr ions is not significantly affected by γ-ray irradiation, further demonstrating the excellent irradiation stability of the o-Tb COF membrane. Based on the above experimental results, a schematic diagram of the separation process was constructed. Figure 11 ).

[0072] Example 4 Separation Mechanism

[0073] To reveal the interaction mechanism between Y ions and COFs, X-ray photoelectron spectroscopy (XPS) was used to study the elemental composition of two membrane materials, ortho-hydroxyl configuration and para-hydroxyl configuration, before and after binding with Y(Ⅲ).

[0074] like Figure 12 As shown in a and 12d, a new Y 3d peak can be observed in the high-resolution XPS spectrum of Y 3d after the static diffusion experiment, proving that Y(Ⅲ) successfully coordinated with the active sites in the pores of the o-Tb COF membrane and p-Tb COF membrane. Figure 12 As shown in c and 12f, the 1s peak of CO in the o-Tb COF film and the p-Tb COF film after strontium-yttrium separation shifts towards a direction with higher binding energy, indicating that the O atoms in the COFs participate in the coordination of Y(III). The N1s spectrum of the o-Tb COF film can form two peaks at 400.3 eV and 399.2 eV, respectively. Figure 12 b), respectively belonging to CN and C=N. After strontium-yttrium separation ( Figure 12 b) The peaks of CN (400.8 eV) and C=N (399.5 eV) shift to higher binding energies, indicating that the N atoms and Y(Ⅲ) in the o-Tb COF film have undergone effective coordination. The N1s XPS spectrum variation trend of the p-Tb COF film is consistent with that of the o-Tb COF film. Figure 12 e).

[0075] Furthermore, theoretical calculations further confirmed the above viewpoints, which were consistent with the experimental results. The calculation results are as follows: Figure 13 As shown. The binding energy of the COF membrane Y(Ⅲ) with the ortho-phenolic hydroxyl configuration is -63.6 kcal mol. -1 The binding energy of the COF membrane Y(Ⅲ) with the para-phenolic hydroxyl configuration is -24.4 kcal mol. -1This indicates that the ortho-hydroxyl configuration has a stronger binding capacity.

[0076] This invention employs a strategy of precisely adjusting the positions of functional groups on the pore walls of COFs, successfully preparing 2D Janus COF membranes with two configurations using the acetic acid buffer interlayer interface method: one with ortho-phenolic hydroxyl groups capable of co-coordinating with ions, and the other with para-phenolic hydroxyl groups lacking this coordination ability. The influence of different coordination structures on Sr / Y separation performance was investigated. The results show that, with the same number of hydroxyl groups, the ortho-phenolic hydroxyl COF membrane has a significantly higher affinity for Y(III) than the para-phenolic hydroxyl COF membrane, mainly because the ortho-phenolic hydroxyl configuration provides additional binding sites. In the Sr / Y separation system, the ortho-phenolic hydroxyl COF membrane achieved a selectivity of 99.7% for Sr(II), maintaining a selectivity of over 95% even after 5 cycles. Conversely, the para-phenolic hydroxyl COF membrane showed a selectivity of only 66.4% for Sr(II). This indicates that the COF membrane with ortho-phenolic hydroxyl groups possesses more multifunctional sites, enhancing its coordination ability for Y(III) and promoting the effective separation of Sr and Y. This invention provides a new approach for the development of porous materials aimed at efficient Sr / Y separation.

[0077] References:

[0078] [1] K. Dey, M. Pal, KCRout, S. Kunjattu H, A. Das, R. Mukherjee, UK Kharul, R. Banerjee, Selective Molecular Separation by Interfacially CrystallizedCovalent Organic Framework Thin Films, J. Am. Chem. Soc. 139 (2017) 13083–13091.

[0079] [2] L.Cao, I.-C.Chen, Z.Li,

[0080] [3]H.L.Nguyen,C.Gropp,O.M.Yaghi,Reticulating 1D Ribbons into 2DCovalent Organic Frameworks by Imine and Imide Linkages,J.Am.Chem.Soc.142(2020)2771–2776。

[0081] [4]P.J.Waller,S.J.Lyle,T.M.Osborn Popp,C.S.Diercks,J.A.Reimer,O.M.Yaghi,Chemical Conversion of Linkages in Covalent Organic Frameworks,J.Am.Chem.Soc.138(2016)15519–15522。

[0082] [5]S.J.Lyle,T.M.O.Popp,P.J.Waller,X.Pei,J.A.Reimer,O.M.Yaghi,Multistep Solid-State Organic Synthesis of Carbamate-Linked Covalent OrganicFrameworks,J.Am.Chem.Soc.(2019)。

Claims

1. A coordinating-enhanced Janus covalent organic framework membrane, characterized in that: Its structure is or ; The specific steps in preparing the synergistically coordinated enhanced Janus covalent organic framework membrane include: a. Dissolve the aldehyde monomer in dichloromethane as the lower organic phase layer, and then slowly add acetic acid as the intermediate buffer aqueous phase layer; b. Dissolve the amine monomer in DMF (N,N-dimethylformamide) solution, and then slowly add it dropwise onto the intermediate buffer aqueous phase layer as the upper organic phase layer; c. The above-mentioned layered mixture was allowed to stand at room temperature for 3 days to react, and then a solid product was obtained at the interface. The product was washed with water and ethanol in sequence to obtain a coordinatingly enhanced Janus covalent organic framework membrane.

2. The Janus covalent organic framework membrane with enhanced coordination according to claim 1, characterized in that: The mass-to-volume ratio of the aldehyde monomer to dichloromethane in step a is 20 mg:60 mL to 60 mg:100 mL.

3. The Janus covalent organic framework membrane with enhanced coordination according to claim 1, characterized in that: The acetic acid mentioned in step a is 6M.

4. The Janus covalent organic framework membrane with enhanced coordination according to claim 1, characterized in that: The mass-to-volume ratio of the amine monomer to DMF in step b is 40 mg:30 mL to 80 mg:70 mL.

5. The Janus covalent organic framework membrane with enhanced coordination according to claim 1, characterized in that: The molar ratio of aldehyde monomer to amine monomer in steps a and b is 1:1.1 to 1:1.

5.

6. The application of the synergistic coordination-enhanced Janus covalent organic framework membrane according to any one of claims 1 to 5 in the preparation of Sr / Y separation materials.

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