Cesium ion-selective separation membrane, and preparation method and application thereof

Abstract

The application discloses a cesium ion selective separation membrane and a preparation method and application thereof, and the separation membrane comprises a self-supporting COF layered skeleton, the self-supporting COF layered skeleton comprises COF nanosheets arranged in an oriented layer, and the inner wall of a channel of the COF nanosheet contains Cs + selective functional groups, and a cross-linked polymer network is filled in an interlayer channel formed between the COF nanosheets; and the thickness of the separation membrane is 50 nm to 20 microns. The cesium ion selective membrane has a limited channel regulation function, a chemical recognition function, a local charge environment regulation function and a structure stabilization function. The separation performance of the membrane can be adjusted by regulating the topological structure, pore size range, functional group type and interlayer cross-linked network composition of the COF nanosheet. The cesium ion can be effectively separated from coexisting ions.

Description

Technical Field

[0001] This invention belongs to the field of functional separation membranes and ion selective separation technology, specifically relating to a Cs... + Selective separation membranes, their preparation methods, and applications. Background Technology

[0002] In the processes of nuclear energy utilization, nuclear fuel reprocessing, and radioactive waste disposal, complex systems containing multiple metal ions are often generated, among which cesium ions are one of the key ions that need to be removed and separated. Especially under conditions of multiple ion coexistence, cesium ions usually exist simultaneously with strontium ions, lanthanum ions, zirconium ions, etc. The differences in valence states, hydration characteristics, and migration behaviors of these ions make them prone to competitive transport during separation, thus increasing the difficulty of selectively separating cesium ions.

[0003] Existing methods for cesium ion separation mainly include precipitation, extraction, ion exchange, adsorption, and membrane separation. Among these, membrane separation has attracted attention due to its relatively simple process and ease of continuous operation. However, for the selective separation of cesium ions from other metal ions, the separation effect is not only related to the membrane pore size but also closely related to the ion's hydration radius, dehydration capacity, local chemical environment within the pores, and the stability of the transport pathway within the membrane. Most conventional polymer separation membranes employ non-specific sieving mechanisms, resulting in wide pore distributions and limited structural uniformity, making it difficult to achieve highly selective separation of cesium ions in complex coexisting ion systems.

[0004] In recent years, covalent organic framework materials (COFs) have been used to construct ion separation membranes due to their designable framework structures and regular pores. Layered membranes formed by stacking two-dimensional COF nanosheets have a certain research foundation in confined transport. However, existing technologies still face the following problems in practical applications: First, the nanosheet layers mainly rely on weak interactions to maintain the stacked structure, which easily leads to interlayer slip, channel size fluctuations, or local defects in solution environments, thus affecting separation stability. Second, although existing COF membranes can improve interfacial interactions by introducing functional groups, the relevant functional sites often lack effective coupling with the actual ion transport channels, making it difficult to simultaneously achieve both transport flux and separation selectivity. Third, some functionalization methods mainly rely on surface modification or simple blending, resulting in uneven distribution of functional sites, limited utilization, and unstable interfacial bonding, which in turn affects the long-term separation performance of the membrane in multi-ion competing systems.

[0005] For the selective separation of cesium ions, relying solely on size sieving or general electrostatic interactions is usually insufficient to achieve ideal results. This is because the transport of cesium ions is limited not only by the pore size but also by their own hydration behavior and the way they interact with functional sites within the membrane. Furthermore, coexisting multivalent ions may preferentially interact with polar groups or charged sites in the membrane, thereby weakening the membrane's ability to preferentially recognize and transport cesium ions. Therefore, current technology still lacks a separation membrane and its preparation method that can both maintain the stability of the layered channel structure and effectively recognize cesium ions during transport.

[0006] Therefore, it is necessary to improve the cesium ion selective separation membrane. This membrane needs to possess the following characteristics simultaneously: first, it should have relatively stable and tunable interlayer transport channels; second, it should have functional sites within the channels or at the interface that selectively act on cesium ions; and third, these functional sites and the membrane's transport structure should form a relatively stable integrated system to reduce the decline in separation performance caused by loose structure, unstable interfaces, or channel distortion during operation. Currently, there is no separation membrane that meets all these requirements. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a cesium ion selective separation membrane, its preparation method and application. The cesium ion selective separation membrane and the cesium ion selective separation membrane prepared by the method have good stability of the layered transport channel structure, can effectively and selectively separate cesium ions from coexisting metal ions, and have stable separation performance.

[0008] To address the above technical problems, this invention first discloses a cesium ion selective separation membrane. This membrane comprises a self-supporting COF layered framework, which includes oriented, layered COF nanosheets. The inner walls of the pores of the COF nanosheets contain Cs... + Selective functional groups fill the interlayer channels formed between COF nanosheets with a cross-linked polymer network; the thickness of the separation membrane is 50 nm to 20 μm.

[0009] Furthermore, the aforementioned Cs + The functional groups with selective effects are one or more of the following: crown ether group, calixarene group, carboxyl group, quaternary ammonium group, sulfonic acid group, phosphonic acid group and hydroxyl group.

[0010] Furthermore, the COF nanosheets have a thickness of 1–10 nm, a lateral dimension of 0.1–10 μm, a pore size of 0.8–2.2 nm, and a topology of hexagonal, tetragonal, rhombic, or Kagome.

[0011] Furthermore, the cross-linked polymer network is obtained by confined cross-linking of a polymer containing at least one functional group of amino, hydroxyl, or carboxyl groups as a polymer precursor and a small molecule compound capable of undergoing a cross-linking reaction with the polymer precursor.

[0012] Furthermore, the polymer precursor is one of polyethyleneimine, polyacrylamide, polyallylamine, polydopamine, chitosan, polyethylene glycol, or polyvinyl alcohol; the crosslinking agent is one of α,α'-dibromo-p-xylene, trimesoyl chloride, terephthaloyl chloride, epichlorohydrin, bisphenol A diglycidyl ether, ethylene glycol diglycidyl ether, glutaraldehyde, or N,N'-methylenebisacrylamide.

[0013] This invention also discloses a method for preparing a cesium ion selective separation membrane as described above.

[0014] The method includes the following steps:

[0015] (1) Preparation of COF nanosheet dispersion with functional groups;

[0016] (2) Add a polymer precursor to the COF nanosheet dispersion in step (1) and mix evenly so that the polymer precursor is adsorbed on the surface of the COF nanosheet and / or enters the pores of the COF nanosheet.

[0017] (3) The COF nanosheet dispersion treated in step (2) is filtered through a porous base membrane using pressure-assisted filtration, causing the COF nanosheets to assemble into an oriented layered structure on the surface of the porous base membrane, and fixing the polymer precursor within the interlayer channels of the COF nanosheets. Specifically, in step (3), after the COF nanosheets are stacked on the surface of the porous base membrane to form a highly oriented layered structure through pressure-assisted filtration, two-dimensional planar gaps are formed between adjacent COF nanosheets. These gaps constitute the space for subsequent confined crosslinking reactions, i.e., interlayer channels, which are also the main channels for ion transport.

[0018] (4) Dissolve the crosslinking agent in a solvent, and filter the resulting crosslinking agent solution through the porous base membrane after step (3) using pressure-assisted filtration, so that the crosslinking agent diffuses into the interlayer channels of the COF nanosheets and undergoes a confined crosslinking reaction with the polymer precursor to obtain a crude COF membrane. The specific reaction in step (4) is epoxy ring-opening reaction, nucleophilic substitution reaction, amidation reaction or free radical polymerization.

[0019] (5) The COF crude membrane obtained in step (4) is cleaned and dried to obtain a COF / polymer integrated composite membrane, namely the cesium ion selective separation membrane.

[0020] Furthermore, in step (1), the concentration of the COF nanosheet dispersion is 0.01–10 mg / mL, and the solvent used for dispersion is one of water, ethanol, methanol, and isopropanol, preferably ethanol; in step (2), the concentration of the polymer precursor in the COF nanosheet dispersion is 0.002–5.0 mg / mL; in step (3), the pressure of the pressure-assisted filtration is 0.5–10 bar, and the pore size of the porous base membrane is in the range of 0.01–1.0 μm, which can effectively trap COF nanosheets and assemble them on the surface.

[0021] Furthermore, the porous base membrane in step (3) is selected from one of the following: polysulfone membrane, polyethersulfone membrane, polyacrylonitrile membrane, polyvinylidene fluoride membrane, polytetrafluoroethylene membrane, nylon membrane, mixed cellulose ester membrane, and alumina ceramic membrane.

[0022] Furthermore, the solvent in step (4) must be able to dissolve the crosslinking agent well, ensuring that it diffuses into the interlayer channels of the COF nanosheets in molecular form; it must not damage the COF backbone and the fixed polymer precursor, and must not cause swelling or collapse of the COF interlayer structure; it must be compatible with the confined polymerization reaction conditions, not participate in side reactions, and be easy to remove in post-processing, specifically one of ethanol, n-hexane, toluene, or a water / ethanol mixture; the pressure of the pressure-assisted filtration is 0.5–10 bar; the reaction temperature of the confined crosslinking reaction is 20–100 °C, preferably 40–80 °C, and the reaction time is 1–48 h, preferably 6–24 h.

[0023] In step (1) of this invention, the COF material used can be synthesized mainly by hot solvent method, in-situ growth method, and interfacial polymerization method. When the monomer used in the synthesis contains the previously described Cs... + When the monomer has a selectively active functional group, COF materials with functional groups can be obtained directly; when the monomer used does not contain the previously mentioned Cs... + When a functional group with selective activity is present, but also contains reactive functional groups (such as alkynyl groups), then post-modification is performed after the synthesis of the COF material to introduce Cs-reactive functional groups. + Functional groups with selective effects are sufficient. The monomers used in the former case, in addition to containing Cs... + The functional groups with selective effects also contain reactive functional groups, and can be further modified to introduce more Cs-dependent functional groups. + Functional groups with selective effects.

[0024] The monomers used in the synthesis are monomers containing ionic groups and complementary monomers. The monomers containing ionic groups are amine monomers, acylhydrazine monomers, or aldehyde monomers containing positively or negatively charged groups. The complementary monomers are aldehyde monomers, amine monomers, or acylhydrazine monomers that can undergo condensation reactions with the monomers containing ionic groups. The amino, acylhydrazine, and aldehyde groups in the monomers containing ionic groups and the complementary monomers participate in the reaction in equimolar amounts.

[0025] Specifically, COF materials can be synthesized by using a solvothermal method to select monomers with reactive functional groups, and then the functional groups can be introduced into the inner wall of the pores of the COF through a post-modification reaction. The COF with the introduced functional groups can then be dispersed in an organic solvent and ultrasonically assisted to exfoliate to obtain a COF nanosheet dispersion with functional groups.

[0026] For example, a condensation reaction is carried out using monomers with functional groups, followed by in-situ growth to obtain a COF nanosheet dispersion with functional groups. When the COF nanosheets also contain reactive functional groups, more functional groups can be introduced through a post-modification reaction. This condensation reaction is carried out under acid catalysis, and after the reaction is completed, the catalyst, unreacted monomers, and oligomers are removed by dialysis.

[0027] The COF nanosheet dispersions prepared by various parties can also be centrifuged, washed, and dried to obtain COF nanosheets for later use. When needed, they can be further dispersed in an organic solvent to obtain a COF nanosheet dispersion with functional groups.

[0028] Examples of structural formulas and abbreviations of the monomers used in the synthesis of COF nanosheets in this invention are as follows:

[0029]

[0030]

[0031]

[0032] The chemical structural formulas and their English abbreviations of the representative COF nanosheets obtained in this invention are shown below:

[0033]

[0034]

[0035]

[0036]

[0037] This invention also discloses a cesium ion selective separation membrane as described above, and the application of the cesium ion selective separation membrane obtained according to the aforementioned preparation method in the selective separation of cesium ions and coexisting metal ions, wherein the coexisting metal ions include Sr. 2+ La 3+ and Zr 4+ One or more of the following; the separation is pressure-driven separation or electric-driven separation.

[0038] The present invention has at least the following effects:

[0039] (1) Limiting channel regulation function

[0040] This invention employs pressure-assisted assembly of COF nanosheets to construct an oriented layered structure, and then forms a cross-linked polymer network in situ within the interlayer channels of the COF nanosheets through confined cross-linking. The resulting composite membrane possesses both an ordered layered framework and a cross-linked network structure, which is beneficial for improving the structural integrity and operational stability of the membrane. Furthermore, it enables effective control over the size, morphology, local chemical environment, and membrane thickness of the ion transport channels within the membrane. After confined cross-linking, the effective transport space of the COF interlayer channels can be further reduced, and the channel distribution tends to be more uniform, thereby enhancing the membrane's sieving effect on different ions and improving the controllability and selectivity of the separation between cesium ions and coexisting metal ions.

[0041] (2) Chemical recognition

[0042] Functional groups, such as crown ethers, calixarenes, carboxyl groups, sulfonic acid groups, phosphonic acid groups, and hydroxyl groups, are introduced into the inner walls of the pores of COF nanosheets to enhance the membrane material's ability to interact with different ions. Specifically, crown ethers and calixarenes can enhance the membrane's recognition of cesium ions; while polar groups such as carboxyl groups and phosphonic acid groups can exert coordination and / or electrostatic interactions with multivalent metal ions. The combination of these chemical recognition effects and confined channel regulation is beneficial for improving the separation performance between cesium ions and coexisting metal ions such as strontium ions, lanthanum ions, and zirconium ions.

[0043] (3) Local charge environment regulation effect

[0044] The polymer precursor introduced in this invention, after crosslinking, can form a crosslinked network containing polar groups and / or ionizable groups within the membrane channel, thereby creating a certain local charge environment within the membrane. Under suitable conditions, this local charge environment can have a differentiated effect on the migration behavior of ions with different valence states, thus facilitating the selective separation of cesium ions from coexisting multivalent metal ions.

[0045] (4) Structural stabilization effect

[0046] This invention utilizes the rigid support of the COF backbone and the polymer network formed by interlayer confined crosslinking to create an integrated structure, which synergistically stabilizes the membrane structure, preventing the loss or uneven distribution of functional sites and improving operational stability. The resulting COF / polymer integrated composite membrane exhibits good density and structural integrity, which helps maintain relatively stable ion transport channels and improves the structural stability and separation performance stability of the membrane in complex ion environments.

[0047] (5) The preparation method of the present invention has clear steps, and the separation performance of the membrane can be adjusted by controlling the topology, pore size range, functional group types and interlayer crosslinking network composition of COF nanosheets. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the process of forming an oriented layered film from COF nanosheets by pressure-assisted assembly in this invention; Figure 2 This is a schematic diagram of the process of preparing composite membrane by confined polymerization within the COF interlayer channels in this invention; Figure 3 This is a scanning electron microscope image of the surface of the 18-crown-6-COF / PEI composite film prepared in Example 1; Figure 4 This is a scanning electron microscope image of a cross section of the 18-crown-6-COF / PEI composite membrane prepared in Example 1; Figure 5 The nitrogen adsorption-desorption isotherm diagram is shown for the 18-crown-6-COF / PEI composite membrane prepared in Example 1. Figure 6 The image shows the pore size distribution of the 18-crown-6-COF / PEI composite membrane prepared in Example 1.

[0049] Figure 1 and Figure 2 The reference numbers are: 1-porous base membrane, 2-COF nanosheet dispersion, 3-COF nanosheets; 4-crosslinking agent solution; 5-crosslinked polymer network. Detailed Implementation

[0050] The present invention will be further explained below with reference to the embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0051] In each embodiment, the porous base membrane is preferably pretreated by soaking in deionized water before use to remove the water-retaining agent.

[0052] Unless otherwise specified, all ion separation performance tests were conducted using a cross-flow filtration device for pressure-driven separation experiments. The feed solution was a mixed solution containing cesium ions and coexisting metal ions, which may include one or more of strontium ions, lanthanum ions, or zirconium ions.

[0053] For the selective separation test of cesium and strontium ions, the concentrations of CsCl and SrCl2 in the feed solution were both 0.1–1 M, the operating pressure was 1–20 bar, and the operating temperature was 10–60 °C. The separation factor α (CsCl2) was used. + / Sr 2+ ) is defined as Cs in the permeate. + With Sr 2+ The concentration ratio divided by the Cs in the feed liquid + With Sr 2+ The concentration ratio. For selective separation tests of cesium ions with lanthanum or zirconium ions, the separation factor is defined in the same way.

[0054] The present invention can also use a multi-ion mixed solution containing CsCl, SrCl2, LaCl3 or ZrCl4 as the feed liquid to evaluate the selective separation performance of the separation membrane of the present invention for cesium ions under multi-ion coexistence conditions.

[0055] Example 1

[0056] (1) Preparation of 18-crown-6 functionalized COF nanosheet dispersion

[0057] First, alkyne-functionalized hexagonal topological TAPB-BPTA-COF powder was synthesized using a solvothermal method. Then, azido-functionalized 18-crown-6 was grafted onto the inner wall of the COF pores via click chemistry to obtain 18-crown-6-functionalized COF powder. 50 mg of the 18-crown-6-functionalized COF powder was dispersed in 100 mL of ethanol, ultrasonically exfoliated for 6 h, and centrifuged to remove unexfoliated particles, yielding a 0.5 mg / mL 18-crown-6-COF nanosheet dispersion. The obtained nanosheets had a thickness of approximately 1 nm and a lateral dimension of approximately 10 μm.

[0058] (2) Adsorption of polymer precursors

[0059] Polyethyleneimine (PEI, molecular weight 600 Da) was added to the above 18-crown-6-COF nanosheet dispersion to make the PEI concentration 0.002 mg / mL, and the mixture was ultrasonically mixed for 2 h to allow PEI to be adsorbed on the surface and inside the pores of the COF nanosheets.

[0060] (3) Pressure-assisted assembly of membrane

[0061] like Figure 1As shown, the COF nanosheet dispersion treated in step (2) is placed on one side of a polyacrylonitrile (PAN) base membrane, and the other side of the PAN membrane is evacuated for pressure filtration. The pore size of the base membrane is 0.1 μm, and the filtration pressure is 0.5 bar, thereby assembling a COF nanosheet oriented layered structure on the surface of the base membrane and fixing PEI within the interlayer channels of the COF. This process is as follows: Figure 2 As shown.

[0062] (4) Confined aggregation

[0063] After step (3), an ethanol solution of α,α'-dibromo-p-xylene (DmX) was placed on one side of the PAN membrane after step (3), and vacuum was continued. The concentration of DmX was 1 mM, and the filtration pressure was 0.5 bar, allowing DmX to diffuse into the COF interlayer channels and undergo a nucleophilic substitution reaction with PEI in the channels. The reaction temperature was 20℃, and the reaction time was 48 h.

[0064] (5) Post-processing

[0065] The obtained membrane was repeatedly washed with ethanol to remove unreacted DmX, byproducts, and the supporting polyacrylonitrile membrane. It was then vacuum dried at 40 °C for 12 h to obtain the 18-crown-6-COF / PEI composite membrane.

[0066] The obtained 18-crown-6-COF / PEI composite membrane was characterized. Scanning electron microscopy results showed that the membrane thickness was approximately 50 nm, and the cross-section exhibited a dense layered structure (e.g., Figure 4 (As shown); nitrogen adsorption test results show that the specific surface area of ​​the membrane is 67 m². 2 The membrane density is 1.25 g / cm³, with a pore size distribution concentrated in the range of 0.8–1.0 nm. 3 The tensile strength is 15 MPa. Scanning electron microscopy images of the 18-crown-6-COF / PEI composite membrane surface show that the composite membrane has good density and structural integrity (e.g., ...). Figure 3 (As shown).

[0067] Ion separation performance test: The feed solution was a mixed solution containing CsCl, SrCl2, LaCl3, and ZrCl4, with each salt concentration of 1 M. The operating pressure was 1 bar, and the operating temperature was 60℃. The separation factor α (CsCl2, SrCl2, LaCl3, and ZrCl4) was measured. + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​are 580, 3400, and 12600 respectively, Cs + The permeation flux is 2.5 mol / (m²). 2The results show that the composite membrane exhibits preferential transport characteristics for cesium ions in multi-ion coexistence systems.

[0068] Example 2

[0069] Cesium ion selective separation membranes were prepared using the same method as in Example 1, except that the COF nanosheets in this example were prepared using an in-situ growth method, and 18-crown-6 functional groups were further introduced into the obtained COF nanosheets. The specific steps are as follows:

[0070] (i) Prepare a BPTA acetonitrile solution with a concentration of 1.5 mmol / L.

[0071] (ii) Prepare an aqueous solution of TAPB with a concentration of 1.0 mmol / L and an aqueous solution of acetic acid with a concentration of 2.0 mol / L.

[0072] (iii) Under stirring conditions, the BPTA acetonitrile solution and the TAPB aqueous solution are mixed dropwise, followed by the addition of an aqueous acetic acid solution.

[0073] (iv) After the addition is complete, the mixed reaction solution is placed at 40°C for 100 h to generate COF-TAPB-BPTA nanosheets.

[0074] (v) The obtained reaction product was dialyzed with distilled water at room temperature for 24 h to remove unreacted monomers, catalysts and oligomers, to obtain a COF-TAPB-BPTA nanosheet dispersion system with reactive groups (alkynyl groups).

[0075] (vi) A click chemistry reaction was performed to graft azide-functionalized 18-crown-6 onto the inner wall of the COF pores, yielding 18-crown-6-functionalized COF nanosheets, which were then dispersed in ethanol to obtain a 18-crown-6-COF nanosheet dispersion with a concentration of 0.8 mg / mL. The resulting nanosheets had a thickness of approximately 10 nm and a lateral dimension of approximately 0.1 μm.

[0076] The subsequent polymer precursor adsorption, pressure-assisted assembly into a membrane, confined polymerization, and post-treatment steps were the same as in Example 1, ultimately yielding an 18-crown-6-COF / PEI composite membrane.

[0077] The obtained membrane was characterized. Scanning electron microscopy results showed that the membrane thickness was approximately 20 μm; nitrogen adsorption tests showed that the specific surface area of ​​the membrane was 63 m². 2 The membrane density is 1.47 g / cm³, with a pore size distribution concentrated between 0.9 and 1.2 nm. 3 The tensile strength is 125 MPa.

[0078] Ion separation performance test: The feed solution was a mixed solution containing CsCl, SrCl2, LaCl3, and ZrCl4, with each salt concentration of 0.1 M. The operating pressure was 5 bar, and the operating temperature was 10℃. The separation factor α (CsCl2, SrCl2, LaCl3, and ZrCl4) was measured. + / Sr 2+ ), α (Cs⁺ / La 3 + ) and α (Cs⁺ / Zr 4+ The values ​​are 1180, 8700, and 21400 respectively, and the Cs⁺ osmotic flux is 0.5 mol / (m²). 2 The results show that the composite membrane exhibits preferential transport characteristics for cesium ions in multi-ion coexistence systems.

[0079] Example 3

[0080] (1) Tetragonal COF-PTA-BPTA powder was synthesized by a solvothermal method, and then carboxyl groups were introduced by a post-modification method to obtain carboxyl-functionalized COF nanosheets. 30 mg of the carboxyl-functionalized COF nanosheets were dispersed in 300 mL of ethanol, and after ultrasonic exfoliation, a COF nanosheet dispersion with a concentration of 0.1 mg / mL was obtained. The thickness of the obtained nanosheets was about 2 nm, and the lateral dimension was about 1 μm.

[0081] (2) Add polyacrylamide (PAM, molecular weight 1500 Da) to the above COF nanosheet dispersion to make the PAM concentration 0.05 mg / mL, mix evenly, and let it adsorb onto the surface and pores of COF nanosheets.

[0082] (3) such as Figure 1 As shown, the COF nanosheet dispersion after step (2) is placed on the side of the polyethersulfone (PES) base membrane for filtration at a pressure of 2 bar, thereby forming an oriented layered membrane structure on the base membrane surface and fixing PAM in the COF interlayer channels.

[0083] (4) After the treatment in step (3), the hexane solution of trimesoyl chloride (TMC) is placed on one side of the membrane obtained in step (3) for further filtration. The concentration of TMC is 5 mM. The reaction is carried out at 40°C for 24 h to allow TMC and PAM to undergo amidation reaction, thereby forming a COF interlayer confined crosslinking network.

[0084] (5) The obtained membrane was washed with ethanol and dried to obtain a carboxyl-functionalized COF / PAM composite membrane.

[0085] The obtained membrane was characterized. Scanning electron microscopy results showed that the membrane thickness was approximately 800 nm; nitrogen adsorption tests showed that the specific surface area of ​​the membrane was 44 m². 2The membrane density is 1.38 g / cm³, with a pore size distribution concentrated in the range of 1.0–1.2 nm. 3 The tensile strength is 60 MPa.

[0086] Ion separation performance test: The feed solution was a mixed solution containing CsCl, SrCl2, LaCl3, and ZrCl4, with each salt concentration of 0.25 M. The operating pressure was 3 bar, and the operating temperature was 25℃. The separation factor α (CsCl2, SrCl2, LaCl3, and ZrCl4) was measured. + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​are 680, 2100, and 9400 respectively, and the Cs⁺ osmotic flux is 1.8 mol / (m²). 2 The results show that the composite membrane exhibits preferential transport characteristics for cesium ions in multi-ion coexistence systems.

[0087] Example 4

[0088] (1) A Kagome-topological COF-ETTA-BPTA was synthesized by in-situ growth and a cup[4]crown-6 functional group was introduced by click chemistry to obtain cup[4]crown-6 functionalized COF nanosheets. 60 mg of the functionalized COF nanosheets were dispersed in 200 mL of ethanol to obtain a COF nanosheet dispersion with a concentration of 0.3 mg / mL. The obtained nanosheets had a thickness of about 5 nm and a lateral dimension of about 6 μm.

[0089] (2) Add polyallylamine (PAH, molecular weight 2000 Da) to the above COF nanosheet dispersion to make the PAH concentration 0.1 mg / mL, mix evenly, and let it adsorb onto the surface and pores of COF nanosheets.

[0090] (3) such as Figure 1 As shown, the mixture obtained in step (2) is placed on one side of the polyvinylidene fluoride (PVDF) base membrane for filtration at a pressure of 4 bar, thereby forming an oriented layered membrane structure on the base membrane surface and fixing the PAH in the interlayer channel of COF.

[0091] (4) Place the toluene solution of terephthaloyl chloride (TPC) on one side of the composite membrane obtained in step (3) and continue filtering. The concentration of TPC is 8 mM. React at 50°C for 18 h to allow TPC to undergo amidation reaction with PAH, thereby forming a COF interlayer confined crosslinking network.

[0092] (5) The obtained membrane was washed with ethanol and dried to obtain cup[4] crown-6 functionalized COF / PAH composite membrane.

[0093] The obtained membrane was characterized. Scanning electron microscopy results showed that the membrane thickness was approximately 800 nm; nitrogen adsorption tests showed that the specific surface area of ​​the membrane was 57 m². 2 The membrane density is 1.45 g / cm³, with a pore size distribution concentrated between 0.9 and 1.1 nm. 3 The tensile strength is 56 MPa.

[0094] Ion separation performance test: The feed solution was a mixed solution containing CsCl, SrCl2, LaCl3, and ZrCl4, with each salt concentration of 0.5 M. The operating pressure was 3 bar, and the operating temperature was 25℃. The separation factor α (CsCl2, SrCl2, LaCl3, and ZrCl4) was measured. + / Sr 2+ ), α (Cs⁺ / La 3 + ) and α (Cs⁺ / Zr 4+ The values ​​are 451, 2090, and 8700 respectively, and the Cs⁺ permeation flux is 2.4 mol / (m²). 2 The results show that the composite membrane exhibits preferential transport characteristics for cesium ions in multi-ion coexistence systems.

[0095] Example 5

[0096] (1) A hexagonal topologically functionalized COF-TP-TF powder with sulfonic acid groups was synthesized by a solvothermal method. 100 mg of the functionalized COF-TP-TF powder was dispersed in 100 mL of ethanol, ultrasonically exfoliated for 6 h, and centrifuged to remove unexfoliated particles, resulting in a COF nanosheet dispersion with a concentration of 1.0 mg / mL. The obtained nanosheets had a thickness of approximately 3 nm and a lateral dimension of approximately 5 μm.

[0097] (2) Add chitosan to the above COF nanosheet dispersion. The degree of deacetylation of the chitosan is 85% (the degree of deacetylation of the chitosan is generally 80-95% to provide sufficient amino reaction sites), and the molecular weight is 5000 Da. Make its concentration 0.5 mg / mL, mix it evenly, and let it adsorb on the surface and inside the pores of the COF nanosheets.

[0098] (3) The mixture obtained in step (2) is placed on one side of the nylon base membrane for filtration at a pressure of 6 bar, thereby forming an oriented layered membrane structure on the base membrane surface and fixing chitosan in the COF interlayer channels.

[0099] (4) Place the water / ethanol mixture of epichlorohydrin (ECH) on one side of the composite membrane obtained in step (3) and continue filtering. The concentration of ECH is 10 mM. React at 60°C for 12 h to allow ECH to cross-link with chitosan, thereby forming a COF interlayer confined cross-linking network.

[0100] (5) The obtained membrane was washed with water and ethanol in sequence and then dried to obtain a sulfonic acid functionalized COF / chitosan composite membrane.

[0101] The obtained membrane was characterized. Scanning electron microscopy results showed that the membrane thickness was approximately 1.5 μm; nitrogen adsorption tests showed that the specific surface area of ​​the membrane was 39 m². 2 The membrane density is 1.52 g / cm³, with a pore size distribution concentrated between 1.2 and 1.5 nm. 3 The tensile strength is 97 MPa.

[0102] Ion separation performance test: The feed solution was a mixed solution containing CsCl, SrCl2, LaCl3, and ZrCl4, with each salt concentration of 0.75 M. The operating pressure was 3 bar, and the operating temperature was 25℃. The separation factor α (CsCl2, SrCl2, LaCl3, and ZrCl4) was measured. + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​are 231, 1290, and 4500 respectively, Cs + The osmotic flux is 3.1 mol / (m²). 2 The results show that the composite membrane exhibits preferential transport characteristics for cesium ions in multi-ion coexistence systems.

[0103] Example 6

[0104] (1) A rhombic topological COF-Py-BPTA was synthesized by in-situ growth, and phosphonic acid groups were introduced by click chemistry to obtain phosphonic acid-functionalized COF nanosheets. 150 mg of the functionalized COF nanosheets were dispersed in 100 mL of water to obtain a COF nanosheet dispersion with a concentration of 1.5 mg / mL. The obtained nanosheets had a thickness of approximately 4 nm and a lateral dimension of approximately 5 μm.

[0105] (2) Add polyvinyl alcohol (PVA, molecular weight 10000 Da) to the above COF nanosheet dispersion to make the PVA concentration 0.8 mg / mL, mix evenly, and let it adsorb onto the surface and pores of COF nanosheets.

[0106] (3) such as Figure 1 After step (2), the COF nanosheet dispersion was placed on one side of the mixed cellulose ester (MCE) base membrane for filtration at a pressure of 8 bar, thereby forming an oriented layered membrane structure on the base membrane surface and fixing PVA in the COF interlayer channels.

[0107] (4) Place the aqueous solution of glutaraldehyde (GA) on one side of the composite membrane obtained in step (3) and continue to filter it. The concentration of GA is 12 mM. React at 70°C for 8 h to allow GA to cross-link with PVA, thereby forming a COF interlayer confined cross-linked network.

[0108] (5) The obtained membrane was washed with water and dried to obtain a phosphonic acid-functionalized COF / PVA composite membrane.

[0109] The obtained membrane was characterized. Scanning electron microscopy results showed that the membrane thickness was approximately 3 μm; nitrogen adsorption tests showed that the specific surface area of ​​the membrane was 79 m². 2 The membrane density is 1.58 g / cm³, with a pore size distribution concentrated between 1.3 and 1.6 nm. 3 The tensile strength is 110 MPa.

[0110] Ion separation performance test: The feed solution was a mixed solution containing CsCl, SrCl2, LaCl3, and ZrCl4, with each salt concentration of 0.25 M. The operating pressure was 3 bar, and the operating temperature was 25℃. The separation factor α (CsCl2, SrCl2, LaCl3, and ZrCl4) was measured. + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​are 734, 6230, and 24100, respectively, and the Cs⁺ osmotic flux is 1.3 mol / (m²). 2 The results show that the composite membrane exhibits preferential transport characteristics for cesium ions in multi-ion coexistence systems.

[0111] Example 7

[0112] (1) A dispersion of 18-crown-6 functionalized COF nanosheets was prepared using the same method as in Example 1, with a concentration of 2.0 mg / mL. The resulting nanosheets had a thickness of approximately 3 nm and a lateral dimension of approximately 6 μm.

[0113] (2) Add polyethylene glycol (PEG, molecular weight 2000 Da) to the above COF nanosheet dispersion to make the PEG concentration 1.0 mg / mL, mix evenly, and let it adsorb onto the surface and pores of COF nanosheets.

[0114] (3) such as Figure 1 After step (2), the COF nanosheet dispersion was placed on one side of the alumina (Al2O3) ceramic substrate membrane for filtration at a pressure of 10 bar, thereby forming an oriented layered membrane structure on the substrate membrane surface and fixing PEG in the COF interlayer channels.

[0115] (4) Place the ethanol solution of bisphenol A diglycidyl ether (BADGE) on one side of the composite membrane obtained in step (3) and continue to filter it. The concentration of BADGE is 15 mM. React at 80°C for 6 h to allow BADGE to cross-link with PEG, thereby forming a COF interlayer confined cross-linking network.

[0116] (5) The obtained membrane was washed with ethanol and then dried to obtain an 18-crown-6-COF / PEG composite membrane.

[0117] The obtained membrane was characterized. Scanning electron microscopy results showed that the membrane thickness was approximately 6 μm; nitrogen adsorption tests showed that the membrane specific surface area was 35 m² / g, with pore size distribution concentrated between 1.4 and 1.8 nm; and the membrane density was 1.62 g / cm³. 3 The tensile strength is 120 MPa.

[0118] Ion separation performance test: The feed solution was a mixed solution containing CsCl, SrCl2, LaCl3, and ZrCl4, with each salt concentration of 0.75 M. The operating pressure was 5 bar, and the operating temperature was 25℃. The separation factor α (CsCl2, SrCl2, LaCl3, and ZrCl4) was measured. + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​are 735, 5260, and 24100 respectively, Cs + The osmotic flux is 1.1 mol / (m²). 2 The results show that the composite membrane exhibits preferential transport characteristics for cesium ions in multi-ion coexistence systems.

[0119] Example 8

[0120] (1) A tetragonal COF-PTA-DHTA with self-contained hydroxyl groups was synthesized by in-situ growth method to obtain hydroxyl-functionalized COF powder. 250 mg of the functionalized COF powder was dispersed in 50 mL of ethanol to obtain a COF nanosheet dispersion with a concentration of 5.0 mg / mL. The obtained nanosheets had a thickness of about 5 nm and a lateral dimension of about 8 μm.

[0121] (2) Add polyethyleneimine (PEI, molecular weight 10000 Da) to the above COF nanosheet dispersion to make the PEI concentration 2.0 mg / mL, mix evenly, and let it adsorb on the surface and inside the pores of COF nanosheets.

[0122] (3) such as Figure 1The COF nanosheet dispersion obtained after step (2) is placed on the side of a polypropylene (PP) base membrane for filtration at a pressure of 8 bar, thereby forming an oriented layered membrane structure on the surface of the base membrane and fixing PEI in the interlayer channels of COF.

[0123] (4) Place the ethanol solution of ethylene glycol diglycidyl ether (EGDE) on one side of the composite membrane obtained in step (3) and continue to filter it. The concentration of EGDE is 20 mM. React at 90°C for 4 h to allow EGDE to cross-link with PEI, thereby forming a COF interlayer confined cross-linking network.

[0124] (5) The obtained membrane was washed with ethanol and then dried to obtain a hydroxyl-functionalized COF / PEI composite membrane.

[0125] The obtained membrane was characterized. Scanning electron microscopy results showed that the membrane thickness was approximately 10 μm; nitrogen adsorption tests showed that the specific surface area of ​​the membrane was 34 m². 2 The membrane density is 1.68 g / cm³, with a pore size distribution concentrated between 1.6 and 2.0 nm. 3 The tensile strength is 130 MPa.

[0126] Ion separation performance test: The feed solution was a mixed solution containing CsCl, SrCl2, LaCl3, and ZrCl4, with each salt concentration of 0.75 M. The operating pressure was 5 bar, and the operating temperature was 25℃. The separation factor α (CsCl2, SrCl2, LaCl3, and ZrCl4) was measured. + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​are 1025, 8260, and 43100 respectively, and the Cs⁺ osmotic flux is 0.6 mol / (m²). 2 The results show that the composite membrane exhibits preferential transport characteristics for cesium ions in multi-ion coexistence systems.

[0127] Example 9

[0128] (1) Using the same method as in Example 3, the functional group was replaced with cup[4]crown-6 to prepare a cup[4]crown-6 functionalized COF nanosheet dispersion with a concentration of 8.0 mg / mL. The resulting nanosheets had a thickness of about 3 nm and a lateral dimension of about 10 μm.

[0129] (2) Add polydopamine (PDA, molecular weight 3000 Da) to the above COF nanosheet dispersion to make the PDA concentration 4.0 mg / mL, mix evenly, and let it adsorb onto the surface and pores of COF nanosheets.

[0130] (3) such as Figure 1After the treatment in step (2), the COF nano-bird dispersion was placed on one side of the polytetrafluoroethylene (PTFE) base membrane for filtration at a pressure of 6 bar, thereby forming an oriented layered membrane structure on the base membrane surface and fixing the PDA in the COF interlayer channel.

[0131] (4) Place an aqueous solution of N,N'-methylenebisacrylamide (MBA) on one side of the composite membrane obtained in step (3) and continue filtering. The MBA concentration is 25 mM. Add ammonium persulfate as an initiator and react at 60°C for 10 h to allow free radical polymerization to occur in the membrane, thereby forming a COF interlayer confined crosslinking network.

[0132] (5) The obtained membrane was washed with water and dried to obtain a cup[4] crown-6 functionalized COF / PDA composite membrane.

[0133] The obtained membrane was characterized. Scanning electron microscopy results showed that the membrane thickness was approximately 15 μm; nitrogen adsorption tests showed that the specific surface area of ​​the membrane was 54 m². 2 The membrane density is 1.72 g / cm³, with a pore size distribution concentrated between 1.5 and 1.9 nm. 3 The tensile strength is 140 MPa.

[0134] Ion separation performance test: The feed solution was a mixed solution containing CsCl, SrCl2, LaCl3, and ZrCl4, with each salt concentration of 0.5 M. The operating pressure was 5 bar, and the operating temperature was 60℃. The separation factor α (CsCl2, SrCl2, LaCl3, and ZrCl4) was measured. + / Sr 2+ ), α (Cs⁺ / La 3 + ) and α (Cs⁺ / Zr 4+ The values ​​are 834, 6130, and 33100, respectively, and the Cs⁺ permeation flux is 2.4 mol / (m²). 2 The results show that the composite membrane exhibits preferential transport characteristics for cesium ions in multi-ion coexistence systems.

[0135] Example 10

[0136] (1) A rhombic topological COF-Py-BPTA was synthesized by in-situ growth and then modified with dibenzo-18-crown-6 functional groups via click chemistry to obtain dibenzo-18-crown-6 functionalized COF powder. 300 mg of the functionalized COF powder was dispersed in 30 mL of ethanol to obtain a COF nanosheet dispersion with a concentration of 10.0 mg / mL. The obtained nanosheets had a thickness of approximately 3 nm and a lateral dimension of approximately 7 μm.

[0137] (2) Add polyethyleneimine (PEI, molecular weight 1800 Da) to the above COF nanosheet dispersion to make the PEI concentration 5.0 mg / mL, mix evenly, and let it adsorb onto the surface and pores of COF nanosheets.

[0138] (3) such as Figure 1 The COF nanosheet dispersion obtained after step (2) is placed on the side of the polysulfone (PSF) base membrane for filtration at a pressure of 10 bar, thereby forming an oriented layered membrane structure on the surface of the base membrane and fixing PEI in the interlayer channels of COF.

[0139] (4) Place an ethanol solution of α,α'-dibromo-p-xylene (DmX) on one side of the composite membrane obtained in step (3) and continue filtering. The concentration of DmX is 30 mM. React at 100°C for 1 h to allow DmX to undergo a nucleophilic substitution reaction with PEI, thereby forming a COF interlayer confined crosslinking network.

[0140] (5) The obtained membrane was washed with ethanol, methanol and DMF in sequence and then dried to obtain a dibenzo-18-crown-6 functionalized COF / PEI composite membrane.

[0141] The obtained membrane was characterized. Scanning electron microscopy results showed that the membrane thickness was approximately 20 μm; nitrogen adsorption tests showed that the specific surface area of ​​the membrane was 51 m². 2 The membrane density is 1.75 g / cm³, with a pore size distribution concentrated between 1.7 and 2.2 nm. 3 The tensile strength is 140 MPa.

[0142] Ion separation performance test: The feed solution was a mixed solution containing CsCl, SrCl2, LaCl3, and ZrCl4, with each salt concentration of 0.5 M. The operating pressure was 20 bar, and the operating temperature was 60℃. The separation factor α (CsCl2, SrCl2, LaCl3, and ZrCl4) was measured. + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​are 517, 4610, and 13700 respectively, and the Cs⁺ osmotic flux is 2.9 mol / (m²). 2 The results show that the composite membrane exhibits preferential transport characteristics for cesium ions in multi-ion coexistence systems.

[0143] Example 11

[0144] (1) COF-Tp-DABA nanosheets with carboxyl functionalization were prepared by in-situ growth and then dispersed in ethanol at a concentration of 0.5 mg / mL. The resulting nanosheets had a thickness of about 3 nm and a lateral dimension of about 7 μm.

[0145] (2) Add polyethyleneimine (PEI, molecular weight 1800 Da) to the above COF nanosheet dispersion to make the PEI concentration 0.2 mg / mL, mix evenly, and let it adsorb onto the surface and pores of COF nanosheets.

[0146] (3) such as Figure 1 The COF nanosheet dispersion obtained after step (2) is placed on the side of a polyacrylonitrile (PAN) base membrane for filtration at a pressure of 1 bar, thereby forming an oriented layered membrane structure on the base membrane surface and fixing PEI in the COF interlayer channels.

[0147] (4) Place an ethanol solution of α,α'-dibromo-p-xylene (DmX) on one side of the composite membrane obtained in step (3) and continue filtering. The concentration of DmX is 2 mM. React at 30°C for 36 h to allow DmX to crosslink with PEI, thereby forming a COF interlayer confined crosslinking network.

[0148] (5) The obtained membrane was washed with ethanol and DMF in sequence and then dried to obtain a carboxyl-functionalized COF / PEI composite membrane.

[0149] The obtained membrane was characterized. Scanning electron microscopy results showed that the membrane thickness was approximately 5 μm; nitrogen adsorption tests showed that the specific surface area of ​​the membrane was 71 m². 2 The membrane density is 1.48 g / cm³, with a pore size distribution concentrated between 1.1 and 1.4 nm. 3 The tensile strength is 110 MPa.

[0150] Ion separation performance test: The feed solution was a mixed solution containing CsCl, SrCl2, LaCl3, and ZrCl4, with each salt concentration of 0.5 M. The operating pressure was 5 bar, and the operating temperature was 25℃. The separation factor α (CsCl2, SrCl2, LaCl3, and ZrCl4) was measured. + / Sr 2+ ), α (Cs⁺ / La 3 + ) and α (Cs⁺ / Zr 4+ The values ​​are 217, 1530, and 7800 respectively, and the Cs⁺ osmotic flux is 1.2 mol / (m²). 2 The results show that the composite membrane exhibits preferential transport characteristics for cesium ions in multi-ion coexistence systems.

[0151] Comparative Example 1

[0152] Comparative tests were conducted using the commercial nanofiltration membrane NF270 (DuPont).

[0153] Ion separation performance test: Under the same test conditions as in Example 1, the Cs⁺ permeation flux was measured to be 1.8 mol / (m²). 2 ·h), separation factor α (Cs) + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​are 8, 35, and 102 respectively.

[0154] Comparative Example 2

[0155] A comparative test was conducted using an 18-crown-6-COF membrane that had not undergone confined polymerization treatment. Compared with Example 1 of the present invention, no PEI was introduced during the film formation process, and no subsequent crosslinking polymerization was performed.

[0156] Ion separation performance test: Under the same test conditions as in Example 1, the Cs⁺ permeation flux was measured to be 7.5 mol / (m²). 2 ·h), separation factor α (Cs) + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​were 11, 56, and 276, respectively. The results indicate that without the construction of an interlayer confined crosslinking network, the intramembrane transport channels are large and lack a dense crosslinking structure, thus its selectivity is significantly lower than that of the composite membrane prepared in this invention.

[0157] Comparative Example 3

[0158] A comparative test was conducted on 18-crown-6-COF / PEI composite membranes prepared by the traditional solution blending method, in which PEI and 18-crown-6-COF were directly mixed in solution and then cast into a membrane without interlayer confinement polymerization.

[0159] Ion separation performance test: Under the same test conditions as in Example 1, Cs was measured. + The permeation flux is 2.3 mol / (m²). 2 ·h), separation factor α (Cs) + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​were 95, 456, and 1350, respectively. The results indicate that, compared to the interlayer confined polymerization method, the composite membrane obtained by the unconfined blending method is less likely to form a stable and uniform interlayer crosslinking network, and therefore its selectivity is lower than that of the composite membrane prepared in this invention.

[0160] Data Analysis

[0161] As can be seen from the above embodiments and comparative data:

[0162] (1) In a multi-ion coexistence system, the separation factor of the COF confined polymerization composite membrane prepared in the embodiments of the present invention is significantly higher than that of the commercial membrane NF270, the pure COF membrane without confined polymerization treatment, and the composite membrane prepared by non-confined blending method, indicating that constructing a confined cross-linking network in the interlayer channel of COF helps to improve the ion separation selectivity of the membrane.

[0163] (2) The type of functional group has a significant impact on the separation performance of the membrane. Crown ether or calix crown ether functionalized membranes, such as those in Examples 1, 2, 4, 7, 9 and 10, generally exhibit a high Cs⁺ preferential transport capacity; carboxyl functionalized membranes, such as those in Examples 3 and 11, also exhibit a high separation factor, indicating that the regulation of the chemical environment within the pores has an important impact on the separation performance.

[0164] (3) The combination of polymer precursor and crosslinking agent has an impact on the final separation performance of the membrane. Different polymer / crosslinking agent systems, such as PEI / DmX, PAM / TMC, PAH / TPC, PDA / MBA, etc., can all form crosslinking networks between COF layers, but their separation effect is also related to the synergistic effect of COF skeleton structure, type of functional groups and confined polymerization conditions.

[0165] (4) The film thickness prepared by the method of the present invention ranges from 50 nm to 20 μm, and the film density is approximately 1.25 to 1.75 g / cm³. 3 This indicates that the method has good control over film thickness and structural density.

[0166] Durability test

[0167] The membrane materials prepared in Examples 1, 3, 8 and 10, as well as the commercial NF270 membrane, were selected and subjected to a durability test for 200 h of continuous operation under the same test conditions as in Example 1.

[0168] Test results showed that after 200 hours of continuous operation, the Cs⁺ permeation flux of the membrane in Example 1 was 2.6 mol / (m²). 2 ·h), separation factor α (Cs) + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​were 573, 3360, and 12580, respectively; in Example 3, after 200 h of continuous membrane operation, the Cs⁺ permeation flux was 1.8 mol / (m²). 2 ·h), separation factor α (Cs) + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+The values ​​were 682, 2086, and 9370, respectively; in Example 8, after 200 h of continuous membrane operation, the Cs⁺ permeation flux was 0.6 mol / (m²). 2 ·h), separation factor α (Cs) + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​were 1011, 8241, and 43005, respectively; in Example 10, after 200 h of continuous membrane operation, the Cs⁺ permeation flux was 3.1 mol / (m²). 2 ·h), separation factor α (Cs) + / Sr 2+ ), α (Cs⁺ / La 3+ ) and α (Cs⁺ / Zr 4+ The values ​​are 497, 4531 and 12600 respectively.

[0169] In contrast, the separation performance of the commercial NF270 membrane decreased significantly after 200 hours of continuous operation, with the separation factor α (Cs) decreasing. + / Sr 2+ () dropped to 1.0.

[0170] The above results show that the COF confined polymerization composite membrane prepared by the present invention can still maintain high ion separation performance under long-term operating conditions, and its structural stability and separation stability are superior to those of commercial membrane materials.

[0171] Results Analysis

[0172] Based on the above embodiments, comparative examples, and durability test results, the following conclusions can be drawn:

[0173] (1) The COF confined polymerization composite membrane provided by this invention exhibits high cesium ion separation selectivity in a multi-ion coexistence system. Among them, α(Cs) + / Sr 2+ The maximum value can reach 1180, which is significantly better than the selected commercial nanofiltration membrane and the control membrane that has not undergone confined polymerization treatment.

[0174] (2) By regulating the topological structure, pore chemical environment and types of functional groups of COF, the present invention can effectively regulate the membrane separation performance; among them, the introduction of functional groups such as crown ether, calix crown ether, carboxyl, sulfonic acid, phosphonic acid and hydroxyl groups is beneficial to improving the membrane’s selective separation ability of Cs⁺ and coexisting metal ions.

[0175] (3) The confined polymerization strategy is an important factor in improving the separation performance of this invention. By constructing a cross-linked polymer network in the interlayer channels of COF, the size of the transport channels and the local chemical environment in the membrane can be effectively adjusted, thereby improving the ion sieving capacity and separation selectivity of the membrane.

[0176] (4) The membrane products prepared by the method of the present invention can achieve effective separation in a wide range of thicknesses, indicating that the method has good membrane structure control capability and process adaptability.

[0177] (5) The COF confined polymerization composite membrane prepared by the present invention can still maintain a high separation factor under long-term operating conditions, indicating that it has good structural stability and separation stability.

Claims

1. A cesium ion selective separation membrane, characterized in that: The separation membrane comprises a self-supporting COF layered framework, which includes oriented, layered COF nanosheets. The inner walls of the pores of the COF nanosheets contain Cs... + Selective functional groups fill the interlayer channels formed between COF nanosheets with a cross-linked polymer network; the thickness of the separation membrane is 50 nm to 20 μm.

2. The cesium ion selective separation membrane according to claim 1, characterized in that: The Cs + The functional groups with selective effects are one or more of the following: crown ether group, calixarene group, carboxyl group, quaternary ammonium group, sulfonic acid group, phosphonic acid group and hydroxyl group.

3. The cesium ion selective separation membrane according to claim 1, characterized in that: The COF nanosheets have a thickness of 1–10 nm, a lateral dimension of 0.1–10 μm, a pore size of 0.8–2.2 nm, and a topology of hexagonal, tetragonal, rhombic, or Kagome.

4. The cesium ion selective separation membrane according to claim 1, characterized in that: The cross-linked polymer network is obtained by confined cross-linking of a polymer containing at least one functional group of amino, hydroxyl, or carboxyl groups as a polymer precursor and a small molecule compound capable of undergoing a cross-linking reaction with the polymer precursor.

5. The cesium ion selective separation membrane according to claim 4, characterized in that: The polymer precursor is one of polyethyleneimine, polyacrylamide, polyallylamine, polydopamine, chitosan, polyethylene glycol, or polyvinyl alcohol; the crosslinking agent is one of α,α'-dibromo-p-xylene, trimesoyl chloride, terephthaloyl chloride, epichlorohydrin, bisphenol A diglycidyl ether, ethylene glycol diglycidyl ether, glutaraldehyde, or N,N'-methylenebisacrylamide.

6. A method for preparing a cesium ion selective separation membrane as described in any one of claims 1-5, characterized in that: The method includes the following steps: (1) Preparation of COF nanosheet dispersion with functional groups; (2) Add a polymer precursor to the COF nanosheet dispersion in step (1) and mix evenly so that the polymer precursor is adsorbed on the surface of the COF nanosheet and / or enters the pores of the COF nanosheet. (3) The COF nanosheet dispersion treated in step (2) is filtered through a porous base membrane using pressure-assisted filtration, so that the COF nanosheets are assembled on the surface of the porous base membrane to form an oriented layered structure, and the polymer precursor is fixed in the interlayer channels of the COF nanosheets. (4) Dissolve the crosslinking agent in a solvent, and filter the resulting crosslinking agent solution through the porous base membrane after step (3) using pressure-assisted filtration, so that the crosslinking agent diffuses into the interlayer channels of the COF nanosheets and undergoes a confined crosslinking reaction with the polymer precursor to obtain a crude COF membrane. (5) The COF crude membrane obtained in step (4) is cleaned and dried to obtain a COF / polymer integrated composite membrane, namely the cesium ion selective separation membrane.

7. The preparation method according to claim 6, characterized in that: The concentration of the COF nanosheet dispersion in step (1) is 0.01 to 10 mg / mL, and the solvent used for dispersion is one of water, ethanol, methanol, and isopropanol; the concentration of the polymer precursor in the COF nanosheet dispersion in step (2) is 0.002 to 5.0 mg / mL; the pressure of the pressure-assisted filtration in step (3) is 0.5 to 10 bar, and the pore size range of the porous base membrane is 0.01 to 1.0 μm.

8. The preparation method according to claim 6 or 7, characterized in that: The porous base membrane in step (3) is selected from one of the following: polysulfone membrane, polyethersulfone membrane, polyacrylonitrile membrane, polyvinylidene fluoride membrane, polytetrafluoroethylene membrane, nylon membrane, mixed cellulose ester membrane, and alumina ceramic membrane.

9. The preparation method according to claim 6, characterized in that: The solvent in step (4) is one of ethanol, n-hexane, toluene, or a water / ethanol mixture. The pressure of the pressure-assisted filtration is 0.5 to 10 bar. The reaction temperature of the confined crosslinking reaction is 20 to 100 °C, and the reaction time is 1 to 48 h.

10. The application of a cesium ion selective separation membrane according to any one of claims 1-5 and a cesium ion selective separation membrane obtained according to the preparation method according to any one of claims 6-9 in the selective separation of cesium ions and coexisting metal ions, wherein the coexisting metal ions include Sr 2+ La 3+ and Zr 4+ One or more of the following; the separation is pressure-driven separation or electric-driven separation.

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