COF-coated POC composite membrane and preparation method and application thereof

Abstract

The invention provides a COF (at) POC composite film and a preparation method and application thereof. The preparation method comprises the following steps: a) dissolving a COF aldehyde monomer and a POC aldehyde monomer in an organic solvent to obtain a first solution; meanwhile, dissolving a COF amine monomer and a POC amine monomer in an organic solvent to obtain a second solution; b) mixing the first solution, the second solution and an acetic acid solution to obtain a homogeneous membrane casting solution; and c) dispensing the homogeneous casting membrane liquid, and reacting to obtain the COF (at) POC composite membrane. Compared with the prior art, the preparation method provided by the invention has the advantages that specific raw materials are matched with specific process steps and conditions, the overall better interaction is realized, and the prepared COF-POC composite membrane is good in mechanical strength and has high ion flux and excellent ion selectivity for monovalent and divalent ion separation; the method has a wide application prospect in the fields of seawater desalination, salt lake lithium extraction, drug separation and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of electrodialysis ion separation, and more specifically, to a COF@POC composite membrane and a preparation method and application thereof. Background Art

[0002] Membrane separation, as a new technology with high efficiency and continuous operation, has the advantages of low energy consumption, simple operation and environmental friendliness, and has great application potential in the field of ion separation. Among separation membranes, polymer membranes dominate the commercial market due to their ease of large-scale production and low production cost. However, it is very difficult to control the pore architecture (pore size, pore morphology, pore dimension and connectivity) of polymer membranes prepared by traditional phase separation methods at the molecular level, and the flexible and random condensed state characteristics hinder the construction of stable sub-nanometer pore structures. Recently, advanced microporous framework materials have become one of the most active research areas, such as covalent organic frameworks (COFs) and porous organic cages (POCs). These microporous framework materials, composed of different organic linkers through covalent bonds, have large porosity, well-defined pore structure, controllable pore size and adjustable ion-specific functional groups, and are advanced candidate materials for the development of separation membranes.

[0003] Covalent organic frameworks (COFs) are continuous crystalline porous materials formed from organic monomers through strong covalent bonds (such as imine and boron-oxygen bonds). Their structures exhibit long-range order, high porosity, high stability, and uniform pore size, enabling the construction of uniform nanochannels and targeted design for separations. Porous organic cage materials are independent cage-like molecules formed from organic molecules through dynamic covalent bonds (such as imine and boronate bonds). Leveraging weak intermolecular interactions (van der Waals forces, hydrogen bonds, and π-π interactions), the cage-like molecules are spatially arranged to form a crystalline porous structure. These structures possess designable nanoscale open cavities (0.5 to 2 nm) and pores, demonstrating broad development prospects in the field of separations.

[0004] Covalent organic frameworks (COFs) and porous organic cages (POCs) are porous organic materials composed of lightweight elements such as C, H, O, and N linked by covalent or dynamic covalent bonds. With their core structures consisting of continuous frameworks and discrete molecular cages, respectively, they exhibit strong complementarity. In particular, the identical covalent bonds in imine-type COFs and imine-type POCs make them highly compatible. Therefore, the construction of separation membrane materials based on COFs and POCs holds great promise for future applications. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a COF@POC composite membrane, a preparation method and application thereof. A COF@POC composite membrane based on covalent organic framework materials and porous organic cage materials is constructed by homogeneous solution polymerization. The membrane has a simple preparation process and good mechanical strength. It exhibits high ion flux and excellent ion selectivity in the separation of monovalent and divalent ions, and has broad application prospects in the fields of concentration-driven membrane separation, electric field-driven membrane separation, and pressure-driven membrane separation.

[0006] The present invention provides a method for preparing a COF@POC composite membrane, comprising the following steps:

[0007] a) dissolving a COF aldehyde monomer and a POC aldehyde monomer in an organic solvent to obtain a first solution; and simultaneously dissolving a COF amine monomer and a POC amine monomer in an organic solvent to obtain a second solution;

[0008] b) mixing the first solution, the second solution and the acetic acid solution to obtain a homogeneous casting solution;

[0009] c) drop-coating the homogeneous casting solution and reacting to obtain a COF@POC composite membrane.

[0010] Preferably, the COF aldehyde monomer in step a) is selected from one or more of 1,3,5-triformylbenzene, tris(4-formylphenyl)amine, 2,4,6-triformylmesitylene, and terephthalaldehyde.

[0011] Preferably, the POC aldehyde monomer in step a) is selected from one or more of trimesaldehyde, 1,3,5-triformylbenzene, 2-hydroxy-1,3,5-trimenesaldehyde, and tris(4-formylphenyl)amine.

[0012] Preferably, the molar ratio of the COF aldehyde monomer to the POC aldehyde monomer in step a) is x:y.

[0013] Preferably, the COF amine monomer in step a) is selected from one or more of 2,5-dimethyl-1,4-phenylenediamine, p-phenylenediamine, tetramethyl-p-phenylenediamine, and 1,3,5-tris(tetraaminophenyl)benzene.

[0014] Preferably, the POC amine monomer in step a) is selected from one or more of 1,2-cyclohexanediamine, 1,2-cyclopentanediamine, 1,2-diaminopropane, and 2-methyl-1,2-propylenediamine.

[0015] Preferably, the organic solvent in step a) is selected from one or more of 1-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, dichloromethane, and chloroform.

[0016] Preferably, the substrate for drop coating in step c) is selected from one of a silicon wafer, a glass substrate, a metal substrate, a ceramic substrate, and a polymer substrate;

[0017] The reaction process is carried out on a heating stage, and the reaction temperature includes but is not limited to 60°C.

[0018] The present invention also provides a COF@POC composite membrane, which is prepared using the preparation method described in the above technical solution.

[0019] The present invention also provides an application of the COF@POC composite membrane described in the above technical solution in ion separation, wherein the application includes concentration-driven membrane separation, electric field-driven membrane separation or pressure-driven membrane separation.

[0020] The present invention provides a COF@POC composite membrane, its preparation method, and application. The preparation method comprises the following steps: a) dissolving COF aldehyde monomer and POC aldehyde monomer in an organic solvent to obtain a first solution; simultaneously, dissolving COF amine monomer and POC amine monomer in an organic solvent to obtain a second solution; b) mixing the first solution, the second solution, and an acetic acid solution to obtain a homogeneous casting solution; and c) drop-coating the homogeneous casting solution and reacting to obtain a COF@POC composite membrane. Compared with the prior art, the preparation method provided by the present invention utilizes specific raw materials in conjunction with specific process steps and conditions to achieve better overall interaction. The prepared COF@POC composite membrane has good mechanical strength, high ion flux and excellent ion selectivity for the separation of monovalent and divalent ions, and has broad application prospects in fields such as seawater desalination, lithium extraction from salt lakes, and drug separation.

[0021] At the same time, the preparation method provided by the present invention has simple process, mild conditions, easy control, universal applicability, and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0023] Figure 1 IR spectra of the TpPa-23@CC32 film in Example 1 of the present invention, the TpPa-2 film in Comparative Example 1, and the CC3 powder in Comparative Example 2;

[0024] Figure 2X-ray diffraction spectra of the TpPa-23@CC32 film in Example 1 of the present invention, the TpPa-2 film in Comparative Example 1, and the CC3 powder in Comparative Example 2;

[0025] Figure 3 In the figure, a and b are scanning electron micrographs of the air-grown surface and the silicon-wafer-grown surface of the TpPa-2 film in Comparative Example 1 of the present invention, respectively; c and d are scanning electron micrographs of the air-grown surface and the silicon-wafer-grown surface of the TpPa-23@CC32 film in Example 1, respectively;

[0026] Figure 4 a and b are scanning electron micrographs of cross sections of the TpPa-2 membrane in Comparative Example 1 and the TpPa-23@CC32 membrane in Example 1, respectively;

[0027] Figure 5 a and b are scanning electron microscope images of the air-grown surface and silicon-wafer-grown surface of the TpTAPB3@CC32 film in Example 2 of the present invention, respectively;

[0028] Figure 6 a and b are scanning electron microscope images of the air-grown surface and silicon-wafer-grown surface of the TpPa-23@CC192 film in Example 3 of the present invention, respectively;

[0029] Figure 7 a and b are scanning electron microscope images of the air-grown surface and silicon-wafer-grown surface of the TpTAPB3@CC192 film in Example 4 of the present invention, respectively;

[0030] Figure 8 For the binary cation system (a) Li + / Mg 2+ and(b)Na + / Ca 2+ The electrodialysis separation results. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] The present invention provides a method for preparing a COF@POC composite membrane, comprising the following steps:

[0033] a) dissolving a COF aldehyde monomer and a POC aldehyde monomer in an organic solvent to obtain a first solution; and simultaneously dissolving a COF amine monomer and a POC amine monomer in an organic solvent to obtain a second solution;

[0034] b) mixing the first solution, the second solution and the acetic acid solution to obtain a homogeneous casting solution;

[0035] c) drop-coating the homogeneous casting solution and reacting to obtain a COF@POC composite membrane.

[0036] The present invention provides a one-step construction of a COF@POC composite membrane based on a covalent organic framework (COF) material and a porous organic cage (POC) material and its ion separation application, belonging to the technical field of novel separation membrane materials. The preparation method mainly comprises: first, dissolving the aldehyde and amine monomers of COF and POC in an organic solvent such as 1-methyl-2-pyrrolidone in turn to obtain a mixed aldehyde solution and a mixed amine solution, respectively; then, blending the mixed aldehyde solution and the mixed amine solution to obtain a homogeneous casting liquid; and dripping the homogeneous casting liquid to prepare a COF@POC composite membrane in one step; by adjusting the ratio of COF and POC monomers in the casting liquid, the membrane channel structure of the COF@POC composite membrane is regulated. The present invention uses a homogeneous solution polymerization method to allow the COF monomer and the POC monomer to react fully and evenly, and the COF framework and POC molecules are arranged in a regular pattern to generate a COF@POC composite membrane. At the same time, the preparation process of the COF@POC composite membrane is simple and has universal applicability. It can be used as a novel ion separation membrane in the fields of concentration-driven membrane separation, electric field-driven membrane separation, and pressure-driven membrane separation.

[0037] The present invention first dissolves COF aldehyde monomer and POC aldehyde monomer in an organic solvent to obtain a first solution (clear and transparent solution); at the same time, COF amine monomer and POC amine monomer are dissolved in an organic solvent to obtain a second solution (clear and transparent solution).

[0038] In the present invention, the COF aldehyde monomer is preferably selected from one or more of 1,3,5-triformylbenzene, tris(4-formylphenyl)amine, 2,4,6-triformylmesitylene, and terephthalaldehyde, and more preferably 1,3,5-triformylbenzene, tris(4-formylphenyl)amine, 2,4,6-triformylmesitylene, or terephthalaldehyde. The present invention has no particular limitation on the source of the COF aldehyde monomer, and commercially available products known to those skilled in the art may be used.

[0039] In the present invention, the POC aldehyde monomer is preferably selected from one or more of trimesicaldehyde, 1,3,5-triformylbenzene, 2-hydroxy-1,3,5-trimenicaldehyde, and tris(4-formylphenyl)amine, and more preferably trimesicaldehyde, 1,3,5-triformylbenzene, 2-hydroxy-1,3,5-trimenicaldehyde, or tris(4-formylphenyl)amine. The present invention has no particular limitation on the source of the POC aldehyde monomer, and commercially available products known to those skilled in the art may be used.

[0040] In the present invention, the molar ratio of the COF aldehyde monomer to the POC aldehyde monomer is preferably x:y, specifically 3:1, 3:2, or 1:1.

[0041] In the present invention, the COF amine monomer is preferably selected from one or more of 2,5-dimethyl-1,4-phenylenediamine, p-phenylenediamine, tetramethyl-p-phenylenediamine, and 1,3,5-tris(tetraaminophenyl)benzene, and more preferably 2,5-dimethyl-1,4-phenylenediamine, p-phenylenediamine, tetramethyl-p-phenylenediamine, or 1,3,5-tris(tetraaminophenyl)benzene. The present invention does not particularly limit the source of the COF amine monomer; commercially available products known to those skilled in the art may be used.

[0042] In the present invention, the POC amine monomer is preferably selected from one or more of 1,2-cyclohexanediamine, 1,2-cyclopentanediamine, 1,2-diaminopropane, and 2-methyl-1,2-propylenediamine, and more preferably 1,2-cyclohexanediamine, 1,2-cyclopentanediamine, 1,2-diaminopropane, or 2-methyl-1,2-propylenediamine. The present invention does not particularly limit the source of the POC amine monomer; commercially available products known to those skilled in the art may be used.

[0043] In the present invention, the molar ratio of the amine monomer to the aldehyde monomer in the COF and POC is the same as that in the imine condensation reaction, and the present invention has no special limitation thereto.

[0044] In the present invention, the organic solvent is preferably selected from one or more of 1-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, dichloromethane, and chloroform, and more preferably 1-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, dichloromethane, or chloroform. The present invention has no particular limitation on the source of the organic solvent, and commercially available products known to those skilled in the art may be used.

[0045] Afterwards, the present invention mixes the first solution, the second solution and the acetic acid solution to obtain a homogeneous casting liquid; in a preferred embodiment of the present invention, 1.5 ml of the aldehyde monomer solution, 1.5 ml of the amine monomer solution and 75 μL of the acetic acid solution (3 mol / L) are mixed and shaken evenly to obtain a homogeneous casting liquid.

[0046] Finally, the present invention drips the homogeneous casting solution and reacts to obtain COF x @POC y Composite membrane.

[0047] In the present invention, the drop-coated substrate is preferably one of a silicon wafer, a glass substrate, a metal substrate, a ceramic substrate, and a polymer substrate, and is more preferably a 2-inch silicon wafer; the reaction process is preferably carried out on a heating table, and the reaction temperature is preferably 60°C, that is, the temperature of the heating table; on this basis, the reaction is carried out, and after evaporating the solvent, it is preferably soaked and washed with deionized water to separate the film from the silicon wafer to obtain COF x @POC y Composite membrane.

[0048] The present invention also provides a COF@POC composite membrane, which is prepared using the preparation method described in the above technical solution.

[0049] The preparation method provided by the present invention adopts specific raw materials in combination with specific process steps and conditions to achieve overall good interaction. The prepared COF@POC composite membrane has good mechanical strength, high ion flux and excellent ion selectivity for the separation of monovalent and divalent ions, and has broad application prospects in the fields of seawater desalination, lithium extraction from salt lakes, and drug separation.

[0050] The present invention also provides an application of the COF@POC composite membrane described in the above technical solution in ion separation, wherein the application includes concentration-driven membrane separation, electric field-driven membrane separation or pressure-driven membrane separation.

[0051] The present invention provides a COF@POC composite membrane, its preparation method, and application. The preparation method comprises the following steps: a) dissolving COF aldehyde monomer and POC aldehyde monomer in an organic solvent to obtain a first solution; simultaneously, dissolving COF amine monomer and POC amine monomer in an organic solvent to obtain a second solution; b) mixing the first solution, the second solution, and an acetic acid solution to obtain a homogeneous casting solution; and c) drop-coating the homogeneous casting solution and reacting to obtain a COF@POC composite membrane. Compared with the prior art, the preparation method provided by the present invention utilizes specific raw materials in conjunction with specific process steps and conditions to achieve better overall interaction. The prepared COF@POC composite membrane has good mechanical strength, high ion flux and excellent ion selectivity for the separation of monovalent and divalent ions, and has broad application prospects in fields such as seawater desalination, lithium extraction from salt lakes, and drug separation.

[0052] At the same time, the preparation method provided by the present invention has simple process, mild conditions, easy control, universal applicability, and broad application prospects.

[0053] To further illustrate the present invention, the following examples are provided for detailed description. The raw materials used in the following examples of the present invention are all commercially available, wherein the COF monomer and POC monomer used are both from Jilin Zhongkeshen Technology Co., Ltd.

[0054] Example 1

[0055] In this embodiment, the COF (TpPa-2) monomers are 1,3,5-triformylbenzene and 2,5-dimethyl-1,4-phenylenediamine, the POC (CC3) monomers are trimesic acid aldehyde and 1,2-cyclohexanediamine, and the organic solvent is NMP. The molar ratios of 1,3,5-triformylbenzene and trimesic acid aldehyde are 3:1, 3:2 and 1:1, respectively.

[0056] A one-step method for constructing a COF@POC composite membrane comprises the following steps:

[0057] 1) 0.2522 g (1.2 mmol) of TpPa-2 aldehyde monomer 1,3,5-triformylbenzene and 0.0649 g (0.4 mmol) of CC3 aldehyde monomer trimesic acid were dissolved in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution; 0.2451 g (1.5 mmol) of TpPa-2 amine monomer 2,5-dimethyl-1,4-phenylenediamine and 0.0685 g (0.6 mmol) of CC3 amine monomer 1,2-cyclohexanediamine were dissolved in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution.

[0058] 2) 1.5 ml of the aldehyde monomer solution, 1.5 ml of the amine monomer solution, and 75 μL of acetic acid solution (3 mol / L) were mixed and shaken evenly. The mixture was drop-coated on a 2-inch silicon wafer and placed on a 60°C heating plate for reaction. After evaporation of the solvent, the membrane was soaked and rinsed with deionized water to separate the membrane from the silicon wafer to obtain a TpPa-23@CC31 composite membrane.

[0059] 3) 0.2522 g (1.2 mmol) of TpPa-2 aldehyde monomer 1,3,5-triformylbenzene and 0.1297 g (0.8 mmol) of CC3 aldehyde monomer trimesic acid were dissolved in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution; 0.2451 g (1.5 mmol) of TpPa-2 amine monomer 2,5-dimethyl-1,4-phenylenediamine and 0.1370 g (1.2 mmol) of CC3 amine monomer 1,2-cyclohexanediamine were dissolved in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution.

[0060] 4) 1.5 ml of the aldehyde monomer solution, 1.5 ml of the amine monomer solution, and 75 μL of acetic acid solution (3 mol / L) were mixed and shaken evenly. The mixture was drop-coated on a 2-inch silicon wafer and placed on a 60°C heating plate for reaction. After evaporation of the solvent, the membrane was soaked and rinsed with deionized water to separate the membrane from the silicon wafer to obtain a TpPa-23@CC32 composite membrane.

[0061] 5) 0.2522 g (1.2 mmol) of TpPa-2 aldehyde monomer 1,3,5-triformylbenzene and 0.1946 g (1.2 mmol) of CC3 aldehyde monomer trimesic acid were dissolved in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution; 0.2451 g (1.5 mmol) of TpPa-2 amine monomer 2,5-dimethyl-1,4-phenylenediamine and 0.2055 g (1.8 mmol) of CC3 amine monomer 1,2-cyclohexanediamine were dissolved in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution.

[0062] 6) 1.5 ml of the aldehyde monomer solution, 1.5 ml of the amine monomer solution, and 75 μL of acetic acid solution (3 mol / L) were mixed and shaken evenly. The mixture was drop-coated on a 2-inch silicon wafer and placed on a 60°C heating plate for reaction. After evaporation of the solvent, the membrane was soaked and rinsed with deionized water to separate the membrane from the silicon wafer to obtain a TpPa-23@CC33 composite membrane.

[0063] Example 2

[0064] In this embodiment, the COF (TpTAPB) monomers are 1,3,5-triformylbenzene and 1,3,5-tris(tetraaminophenyl)benzene, the POC (CC3) monomers are trimesic acid aldehyde and 1,2-cyclohexanediamine, and the organic solvent is NMP. The molar ratio of 1,3,5-triformylbenzene to trimesic acid aldehyde is 3:2.

[0065] 1) Dissolve 0.2522 g (1.2 mmol) of TpTAPB aldehyde monomer 1,3,5-triformylbenzene and 0.1297 g (0.8 mmol) of CC3 aldehyde monomer trimesic acid in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution; dissolve 0.4217 g (1.2 mmol) of TpTAPB amine monomer 1,3,5-tris(tetraaminophenyl)benzene and 0.1370 g (1.2 mmol) of CC3 amine monomer 1,2-cyclohexanediamine in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution.

[0066] 2) 1.5 ml of the aldehyde monomer solution, 1.5 ml of the amine monomer solution, and 75 μL of acetic acid solution (3 mol / L) were mixed and shaken evenly. The mixture was drop-coated on a 2-inch silicon wafer and placed on a 60°C heating table for reaction. After evaporation of the solvent, the membrane was soaked and rinsed with deionized water to separate the membrane from the silicon wafer to obtain a TpTAPB3@CC32 composite membrane.

[0067] Example 3

[0068] In this embodiment, the COF (TpPa-2) monomers used are 1,3,5-triformylbenzene and 2,5-dimethyl-1,4-phenylenediamine, the POC (CC19) monomers used are 2-hydroxy-1,3,5-triformylbenzene and 1,2-cyclohexanediamine, and the organic solvent used is NMP. The molar ratio of 1,3,5-triformylbenzene to 2-hydroxy-1,3,5-triformylbenzene is 3:2.

[0069] 1) 0.2522 g (1.2 mmol) of TpPa-2 aldehyde monomer 1,3,5-triformylbenzene and 0.1425 g (0.8 mmol) of CC19 aldehyde monomer 2-hydroxy-1,3,5-benzenetricarbaldehyde were dissolved in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution; 0.2451 g (1.5 mmol) of TpPa-2 amine monomer 2,5-dimethyl-1,4-phenylenediamine and 0.1370 g (1.2 mmol) of CC19 amine monomer 1,2-cyclohexanediamine were dissolved in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution.

[0070] 2) 1.5 ml of the aldehyde monomer solution, 1.5 ml of the amine monomer solution, and 75 μL of 3 mol / L acetic acid solution were mixed and shaken until uniform. The mixture was drop-coated on a 2-inch silicon wafer and placed on a 60°C heating plate for reaction. After evaporation of the solvent, the membrane was soaked and rinsed with deionized water to separate the membrane from the silicon wafer to obtain a TpPa-23@CC192 composite membrane.

[0071] Example 4

[0072] In this embodiment, the COF (TpTAPB) monomers used are 1,3,5-triformylbenzene and 1,3,5-tris(tetraaminophenyl)benzene, the POC (CC19) monomers used are 2-hydroxy-1,3,5-triformylbenzene and 1,2-cyclohexanediamine, and the organic solvent used is NMP. The molar ratio of 1,3,5-triformylbenzene to 2-hydroxy-1,3,5-triformylbenzene is 3:2.

[0073] 1) Dissolve 0.2522 g (1.2 mmol) of TpTAPB aldehyde monomer 1,3,5-triformylbenzene and 0.1425 g (0.8 mmol) of CC19 aldehyde monomer 2-hydroxy-1,3,5-benzenetricarbaldehyde in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution; dissolve 0.4217 g (1.2 mmol) of TpTAPB amine monomer 1,3,5-tris(tetraaminophenyl)benzene and 0.1370 g (1.2 mmol) of CC19 amine monomer 1,2-cyclohexanediamine in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution.

[0074] 2) 1.5 ml of the aldehyde monomer solution, 1.5 ml of the amine monomer solution, and 75 μL of acetic acid solution (3 mol / L) were mixed and shaken evenly. The mixture was drop-coated on a 2-inch silicon wafer and placed on a 60°C heating plate for reaction. After evaporation of the solvent, the membrane was soaked and rinsed with deionized water to separate the membrane from the silicon wafer to obtain a TpTAPB3@CC192 composite membrane.

[0075] Example 5

[0076] In this embodiment, the COF (TpPa-2) monomers are 1,3,5-triformylbenzene and 2,5-dimethyl-1,4-phenylenediamine, the POC (CC3) monomers are trimesic acid aldehyde and 1,2-cyclohexanediamine, and the organic solvent is DMSO. The molar ratio of 1,3,5-triformylbenzene to trimesic acid aldehyde is 3:2.

[0077] 1) 0.2522 g (1.2 mmol) of TpPa-2 aldehyde monomer 1,3,5-triformylbenzene and 0.1297 g (0.8 mmol) of CC3 aldehyde monomer trimesic acid were dissolved in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution; 0.2451 g (1.5 mmol) of TpPa-2 amine monomer 2,5-dimethyl-1,4-phenylenediamine and 0.1370 g (1.2 mmol) of CC3 amine monomer 1,2-cyclohexanediamine were dissolved in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution.

[0078] 2) 1.5 ml of the aldehyde monomer solution, 1.5 ml of the amine monomer solution, and 75 μL of acetic acid solution (3 mol / L) were mixed and shaken evenly. The mixture was drop-coated on a 2-inch silicon wafer and placed on a 60°C heating plate for reaction. After evaporation of the solvent, the membrane was soaked and rinsed with deionized water to separate the membrane from the silicon wafer to obtain a TpPa-23@CC32(DMSO) composite membrane.

[0079] Comparative Example 1

[0080] In this embodiment, the COF (TpPa-2) monomers are 1,3,5-triformylbenzene and 2,5-dimethyl-1,4-phenylenediamine, and the organic solvent is 1-methyl-2-pyrrolidone.

[0081] The preparation method of the TpPa-2COF membrane comprises the following steps:

[0082] 1) 0.2522 g (1.2 mmol) of TpPa-2 aldehyde monomer 1,3,5-triformylbenzene was dissolved in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution; 0.2451 g (1.5 mmol) of TpPa-2 amine monomer 2,5-dimethyl-1,4-phenylenediamine was dissolved in 40 mL of 1-methyl-2-pyrrolidone to obtain a clear and transparent solution.

[0083] 2) 1.5 ml of aldehyde monomer solution, 1.5 ml of amine monomer solution, and 75 μL of acetic acid solution (3 mol / L) were mixed, shaken evenly, and drop-coated on a 2-inch silicon wafer. The mixture was placed on a 60°C heating table for reaction. After evaporation of the solvent, the membrane was soaked and rinsed with deionized water to separate the membrane from the silicon wafer to obtain a TpPa-2 COF membrane.

[0084] Comparative Example 2

[0085] In this embodiment, the POC (CC3) monomers are trimesaldehyde and 1,2-cyclohexanediamine, and the organic solvent is dichloromethane.

[0086] The preparation method of CC3 crystal comprises the following steps:

[0087] 1) Dissolve 2 g of trimesaldehyde in 40 mL of dichloromethane to obtain a clear and transparent aldehyde solution, and then add 40 μL of trifluoroacetic acid to the aldehyde solution; separately, dissolve 2 g of 1,2-cyclohexanediamine in 40 mL of dichloromethane to obtain a clear and transparent amine solution.

[0088] 2) The aldehyde solution and the amine solution were uniformly mixed and reacted at room temperature. After 4 days, CC3 crystal particles were collected by centrifugation, washed with 95% ethanol / 5% dichloromethane, and finally dried in vacuo at 60°C.

[0089] Membrane characterization and testing:

[0090] In order to characterize the surface morphology of the membrane, Figure 3 From the surface electron microscopy image, we can find that the air growth surface of TpPa-23@CC32 membrane presents a dense network structure, while the silicon growth surface of TpPa-23@CC32 membrane presents a dense film layer, compared with the loose fibrous structure of TpPa-2. Therefore, the addition of CC3 monomer solution to the COF monomer solution significantly enhances the density of the membrane. Figure 4 The cross-sectional electron microscopy in the figure also shows that compared with the loose membrane structure of TpPa-2, after adding CC3 monomer in the reaction, the thickness of TpPa-23@CC32 membrane decreases and the membrane structure becomes uniform and dense.

[0091] To further characterize the membrane structure, e.g. Figure 1 As shown in the figure, we tested the infrared spectra of the TpPa-23@CC32 film in Example 1, the TpPa-2 film in Comparative Example 1, and the CC3 powder in Comparative Example 2. After the CC3 monomer was added to react to form the TpPa-23@CC32 film, the TpPa-23@CC32 film would have a peak at 1545 cm -1 The C=C characteristic peak of TpPa-2 membrane is retained at 1595 cm -1The C=N characteristic peak of CC3 is retained at 2900 cm -1 The unique alkane CH stretching vibration peak in CC3 appeared near the surface, proving that TpPa-2 and CC3 were combined to form TpPa-23@CC32 membrane. Figure 2 As shown, the X-ray diffraction spectra of the TpPa-23@CC32 film prepared in Example 1, the TpPa-2 film in Comparative Example 1, and the CC3 powder in Comparative Example 2 also prove the above point of view.

[0092] For the membrane ion separation performance test, we selected 0.1 mol / L LiCl / MgCl2 and NaCl / CaCl2 as the target salt solutions:

[0093] Electrodialysis was performed using a 100ml electrodialysis apparatus with a 0.3 mol / L Na2SO4 solution in the anode and cathode chambers, a 0.1 mol / L LiCl / MgCl2 or NaCl / CaCl2 salt solution in the desalination chamber, and a 0.001 mol / L KCl solution in the concentrating chamber. The anion exchange membrane used was ASTOM's AGU anion exchange membrane, and the TpPa-2@CC3 membrane prepared in this embodiment of the present invention served as the separation membrane. The test lasted 0.5 hours. The cation concentration in the concentrating chamber was measured using ICP-AES, and the flux and selectivity of each cation were calculated based on the concentration.

[0094] From the test results, we can find that Figure 8 As shown in the figure, the addition of CC3 monomer in the reaction significantly improves the ion separation performance of the membrane, and the ion flux decreases slightly compared with the TpPa-2 membrane. Therefore, the prepared TpPa-23@CC32 membrane has the advantages of both high selectivity and high flux.

[0095] The preparation methods used in Examples 1, 2, 3, 4, and 5 are very similar. They are all based on the homogeneous solution polymerization method of COF and POC materials to construct COF@POC composite membranes. Example 1 changes the molar ratio of CC3 monomer to COF monomer in the reaction; Example 2 changes the COF monomer in the reaction; Example 3 changes the POC monomer in the reaction; Example 4 changes the COF monomer and POC monomer in the reaction; Example 5 changes the organic solvent in the reaction. Figures 5-7As shown, under the adjustment of these parameters, COF@POC composite membranes with dense and uniform morphology can be prepared, reflecting the universality of the present invention. The present invention adheres to the concept that structure determines performance. Starting from the characteristics that the pore size of two-dimensional COF membrane materials is usually above 1nm and the film-forming property of POC materials is poor, discrete POC cage structures are introduced into two-dimensional COF channels for the first time to construct uniform angstrom-scale confined ion transport channels, and COF@POC composite membranes with excellent ion selectivity and high ion flux are prepared. The preparation process of this composite membrane is simple, and it is generally designable as in the examples. It can be introduced into the preparation of different types of COF@POC composite membranes, and can be used in a directionally realized manner for different separation systems. It has broad application prospects in the fields of concentration-driven membrane separation, electric field-driven membrane separation, and pressure-driven membrane separation.

[0096] The above description of the disclosed embodiments will enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a COF@POC composite membrane, characterized in that: The following steps are involved: a) dissolving a COF aldehyde monomer and a POC aldehyde monomer in an organic solvent to obtain a first solution; and simultaneously dissolving a COF amine monomer and a POC amine monomer in an organic solvent to obtain a second solution; b) mixing the first solution, the second solution and the acetic acid solution to obtain a homogeneous casting solution; c) drop-coating the homogeneous casting solution and reacting to obtain a COF@POC composite membrane.

2. The preparation method according to claim 1, characterized in that The COF aldehyde monomer in step a) is selected from one or more of 1,3,5-triformylbenzene, tris(4-formylphenyl)amine, 2,4,6-triformylmesitylene, and terephthalaldehyde.

3. The preparation method according to claim 1, characterized in that The POC aldehyde monomer in step a) is selected from one or more of trimesaldehyde, 1,3,5-triformylbenzene, 2-hydroxy-1,3,5-trimenesaldehyde, and tris(4-formylphenyl)amine.

4. The preparation method according to claim 1, characterized in that The molar ratio of the COF aldehyde monomer to the POC aldehyde monomer in step a) is x:y, including but not limited to 3:1, 3:2, and 1:

1.

5. The preparation method according to claim 1, characterized in that The COF amine monomer in step a) is selected from one or more of 2,5-dimethyl-1,4-phenylenediamine, p-phenylenediamine, tetramethyl-p-phenylenediamine, and 1,3,5-tris(tetraaminophenyl)benzene.

6. The preparation method according to claim 1, characterized in that The POC amine monomer in step a) is selected from one or more of 1,2-cyclohexanediamine, 1,2-cyclopentanediamine, 1,2-diaminopropane, and 2-methyl-1,2-propylenediamine.

7. The preparation method according to claim 1, characterized in that The organic solvent in step a) is selected from one or more of 1-methyl-2-pyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, dichloromethane, and chloroform.

8. The preparation method according to claim 1, characterized in that The substrate for drop coating in step c) is selected from one of a silicon wafer, a glass substrate, a metal substrate, a ceramic substrate, and a polymer substrate; The reaction process is carried out on a heating stage, and the reaction temperature includes but is not limited to 60°C.

9. A COF@POC composite membrane, characterized in that: The preparation method is described in any one of claims 1 to 8.

10. Use of the COF@POC composite membrane according to claim 9 in ion separation, characterized in that: The applications include concentration driven membrane separation, electric field driven membrane separation or pressure driven membrane separation.

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