Click chemistry functionalized covalent organic framework membrane and preparation method and application thereof

Abstract

This invention relates to a click chemistry-functionalized covalent organic frame membrane, its preparation method, and its application, belonging to the field of membrane separation technology. The invention first synthesizes a COF material, and then precisely introduces three functional groups—sulfonic acid, carboxyl, and amino—with different electronegativity and coordination abilities into the COF channels through click chemistry, respectively, to obtain a series of COF membranes (TADA-R membranes) with continuous channels. The click chemistry-functionalized covalent organic frame membrane of this invention can be used in Li... + / Mg 2+ Separation allows for the independent and systematic study of the effects of changes in the chemical properties of the pore surface on the selective transport of lithium and magnesium ions, while maintaining the COF framework structure and pore size.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a click chemistry functionalized covalent organic frame membrane, its preparation method, and its application. Background Technology

[0002] High-efficiency energy storage technology is key to achieving sustainable development. Lithium-ion batteries, as the core energy storage carrier, are widely used in electric vehicles and smart grids, driving the continuous and rapid growth in demand for lithium resources. Salt lake brines account for approximately 60% of global lithium reserves, possessing advantages such as large reserves and low extraction costs, making them an important source of future lithium supply. However, the lithium concentration in salt lake brines is generally low (typically 100-1000 mg / L), and is accompanied by high concentrations of coexisting ions such as magnesium ions (Mg... 2+ / Li + The high concentration of lithium (tens to hundreds of times higher) severely restricts the efficient separation and enrichment of lithium. Traditional separation methods (such as solvent extraction, precipitation, and ion exchange) suffer from poor selectivity, high reagent consumption, and limited scalability. In contrast, membrane separation technology, with its advantages of low energy consumption, continuous process, and environmental friendliness, is considered an important direction for achieving green extraction of lithium resources (Adv. Mater. 2025, 37, 2501881).

[0003] Ideal ion separation membranes require precise pore structures to distinguish hydrated ions of different sizes, and specific chemical environments to differentially regulate the transport behavior of different ions. However, traditional polymer membranes typically struggle to achieve precise control over pore size and have relatively limited chemical functions, restricting further improvements in their separation performance. Covalent organic frameworks (COFs) are a class of crystalline porous materials formed by organic structural units linked by strong covalent bonds. They possess well-defined pore structures and tunable pore sizes, providing an ideal platform for achieving precise size sieving. Furthermore, the designability of the COF framework lays the foundation for the targeted modification of its pore chemical environment. Therefore, developing COF-based separation membranes holds promise for achieving precise control over pore size and flexible regulation of surface chemical properties in a single material system, thereby overcoming the performance bottlenecks of existing lithium-magnesium separation technologies.

[0004] However, relying solely on precise physical pore size sieving is insufficient for achieving efficient separation of lithium and magnesium ions. Although lithium ions (Li... + ) and magnesium ions (Mg 2+ The difference in hydration radius between Mg and Mg makes sieving possible, but Mg 2+With higher charge density, ions tend to have stronger non-specific interactions with the membrane pore surface, easily leading to increased transport resistance or even pore blockage. More importantly, in the harsh environment of high magnesium-to-lithium ratios, selectivity based solely on size differences is limited. Therefore, actively introducing specific charged functional groups into the COF pores to differentially regulate ion transport behavior through controllable electrostatic interactions has become a core strategy for overcoming selectivity bottlenecks. For example, introducing negatively charged sulfonic acid or carboxyl groups can effectively suppress high charge density Mg2+ ions through electrostatic repulsion. 2+ Entering the pores simultaneously reduces the hindrance to Li⁺; while introducing positively charged amino groups may achieve selective promotion through differences in the strength of coordination interactions. This charge-effect-based chemical recognition mechanism, working synergistically with the size sieving physical mechanism, is key to achieving highly selective separation (Adv. Mater. 2025, 37, 2414898). Currently, most functionalization strategies for COF membranes rely on the pre-design of monomers before synthesis, meaning that functional groups are introduced simultaneously with framework construction, making it difficult to further adjust the chemical properties of the membrane after formation. This "one-step" approach limits the systematic study of the structure-activity relationship between functional group type and separation performance based on the same pore structure, hindering rapid material optimization and in-depth understanding of the mechanism. To overcome this limitation, post-synthetic modification strategies have gradually gained attention (Nat. Water 2025, 3, 191–200), among which click chemistry, due to its advantages of high reaction efficiency, mild conditions, and broad functional group compatibility, has become a powerful tool for achieving precise functionalization of COF materials. Summary of the Invention

[0005] This invention aims to address a key problem in most current COF membrane functionalization strategies. Currently, these strategies typically rely on the pre-design of monomers before synthesis, i.e., the simultaneous introduction of functional groups during framework construction. However, this approach makes it difficult to further adjust the chemical properties of the membrane material after molding, creating a "one-step" limitation. This limitation not only hinders the systematic exploration of the structure-activity relationship between functional group type and separation performance based on the same pore structure, but also significantly slows down the rapid optimization process of materials. Therefore, this invention provides a click chemistry-functionalized covalent organic framework membrane, its preparation method, and its applications. A more flexible functionalization method was developed, first successfully synthesizing a COF parent membrane with a regular pore structure and reactive vinyl groups. These vinyl groups act as "chemical handles" installed within the pores, providing reaction sites for subsequent functionalization modifications. Based on this, this invention utilizes efficient and mild click chemistry reactions to precisely introduce three functional groups—sulfonic acid, carboxyl, and amino—with different electronegativity and coordination abilities into the COF pores. The advantage of this method is that it can independently and systematically study the effects of changes in the chemical properties of the pore surface on the selective transport of lithium and magnesium ions while keeping the COF framework structure and pore size unchanged.

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

[0007] The first objective of this invention is to provide a method for preparing click chemistry-functionalized covalent organic frame membranes (flowchart shown below). Figure 1 (As shown), including the following steps:

[0008] S1. The polyacrylonitrile substrate was immersed in a dopamine / tris(hydroxymethyl)aminomethane hydrochloride buffer solution to react and obtain a dopamine-modified PAN porous support.

[0009] S2. Under a protective atmosphere, the dopamine-modified PAN porous support obtained in step S1 is reacted with 3-aminopropyltriethoxysilane in the first solvent by heating to obtain an amino-modified PAN porous support.

[0010] S3. The amino-modified PAN porous support is reacted with 2,5-divinyl terephthalaldehyde in a second solvent by heating to obtain a vinyl-functionalized support.

[0011] S4. The vinyl-functionalized support obtained in step S3 is mixed with tris(4-aminophenyl)amine and 2,5-divinyl terephthalaldehyde in a third solvent and reacted under the action of acetic acid to obtain a vinyl-functionalized COF composite film.

[0012] S5. Under a protective atmosphere, the vinyl-functionalized COF composite film obtained in step S4 is subjected to a click chemical reaction with the functionally modified monomer in a fourth solvent to obtain the click chemically functionalized covalent organic frame film; the functionally modified monomer is one or more of sodium 2-mercaptoethanesulfonate, cysteine ​​hydrochloride and mercaptoacetic acid.

[0013] In one embodiment of the present invention, in step S1, the concentration of dopamine in the dopamine / tris(hydroxymethyl)aminomethane hydrochloride buffer solution is 7.5 mg / mL to 8.5 mg / mL.

[0014] In one embodiment of the present invention, in step S2, the concentration of 3-aminopropyltriethoxysilane is 0.15 mmol to 0.25 mmol.

[0015] In one embodiment of the present invention, in step S2, the first solvent is isopropanol and / or ethanol.

[0016] And / or, the conditions for the heating reaction are: heating in an oil bath at 50°C for 3 hours.

[0017] In one embodiment of the present invention, in step S3, the concentration of 2,5-divinyl terephthalaldehyde is 0.9 mg / mL to 1.1 mg / mL.

[0018] In one embodiment of the present invention, in step S3, the second solvent is 1,4-dioxane;

[0019] And / or, the conditions for the heating reaction are: heating at 60℃-65℃ for 4 h-4.5 h.

[0020] In one embodiment of the present invention, in step S4, the ratio of the total mass of the tris(4-aminophenyl)amine and 2,5-divinyl terephthalaldehyde to the surface area of ​​the vinyl-functionalized carrier is 12-13 mg / cm². -2 ;

[0021] And / or, the third solvent is 1,4-dioxane and mesitylene; the volume ratio of 1,4-dioxane to mesitylene is 4:1;

[0022] And / or, the reaction conditions are: 120°C for 3 days.

[0023] In one embodiment of the present invention, the fourth solvent is selected from one or more of aqueous ethanol, methanol, and tetrahydrofuran;

[0024] And / or, the conditions for the click chemical reaction are: 60℃-70℃ for 12 h-24 h.

[0025] A second objective of this invention is to provide click-chemically functionalized covalent organic frame membranes obtained by the aforementioned preparation method.

[0026] A third objective of this invention is to provide the aforementioned click chemistry functionalized covalent organic frame membrane in Li + / Mg 2+ Applications in separation.

[0027] Compared with the prior art, the above-described technical solution of the present invention has the following advantages:

[0028] (1) Flexible and controllable functionalization: By adopting the post-modification strategy of click chemical synthesis, different functional groups such as sulfonic acid group, carboxyl group, and amino group can be introduced independently and precisely while keeping the COF skeleton structure and pore size unchanged. This breaks through the limitations of traditional "one-step" functionalization, facilitates systematic study of structure-property relationship, and accelerates material optimization.

[0029] (2) Significantly improved lithium-magnesium separation performance: The dual mechanism of synergistic pore size sieving and electrostatic / coordination chemical recognition effectively suppresses high charge density Mg 2+ Transmission, priority promotion of Li + By achieving highly selective separation in brine from salt lakes with a high magnesium-to-lithium ratio, the separation factor and ion permeability are superior to those of existing COF membranes.

[0030] (3) Mild reaction conditions and strong universality: Click chemistry reaction is efficient, mild, and has wide functional group compatibility. It does not require harsh high temperature and high pressure, is suitable for large-scale preparation, and can flexibly switch functional group types to adapt to different separation scenarios. Attached Figure Description

[0031] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0032] Figure 1 This is a schematic diagram of the synthetic route of covalent organic framework membranes based on click chemistry modification according to the present invention;

[0033] Figure 2 These are SEM images of the cross-sections (f) of DVA-PAN (a), TADA (b), TADA-NH2 (c), TADA-SO3H (d), TADA-COOH (e), and TADA-SO3H of the present invention;

[0034] Figure 3 The desalination performance (a) of different types of membranes in this invention and the performance of TADA-SO3H with different grafting amounts (x represents the initial feed amount of different 2-mercaptoethanesulfonate, in g). Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0036] This invention first synthesizes COF materials, and then precisely introduces three functional groups with different electronegativity and coordination ability—sulfonic acid group, carboxyl group, and amino group—into the COF channels through click chemistry to obtain a series of COF membranes (TADA-R membranes) with continuous channels.

[0037] In preparing the functionalized covalent organic framework membrane of this invention, firstly, a polyacrylonitrile porous membrane is used as a substrate, and the substrate is modified with a dopamine / tris(hydroxymethyl)aminomethane hydrochloride buffer solution to obtain a dopamine-modified polyacrylonitrile (PAN) support; then, isopropanol is used as a solvent and 3-aminopropyltriethoxysilane (APTES) is used as a modifying agent, and the reaction is carried out in an oil bath under a nitrogen atmosphere. After washing with isopropanol, the membrane is vacuum dried to obtain an aminated modified support; further, 1,4-dioxane is used as a solvent and 2,5-divinyl terephthalaldehyde (DVA) is used as a reactant, and the reaction is carried out under heating. After washing with solvent and drying, a vinyl functionalized support is obtained. Using tris(4-aminophenyl)amine (TAA) and DVA as comonomers, and 1,4-dioxane and mesitylene in a volume ratio of 4:1 as solvents, with acetic acid added as a catalyst, the mixture was ultrasonically dispersed and placed in a reactor for constant temperature reaction. After the reaction, the mixture was washed sequentially with 1,4-dioxane and ethanol, and then vacuum dried to prepare a vinyl-functionalized COF composite membrane (TADA membrane). Based on this, using azobisisobutyronitrile (AIBN) as an initiator, under a nitrogen atmosphere, sodium 2-mercaptoethanesulfonate, cysteine ​​hydrochloride, and mercaptoacetic acid were selected as functional modifying monomers, and corresponding solvent systems of ethanol-water solution, methanol, and tetrahydrofuran were matched for click chemistry reactions, with reaction times ranging from 12 to 24 h. After the reaction, the mixture was thoroughly washed with the corresponding solvents and dried to obtain functionalized COF membranes modified with sulfonic acid, amino, and carboxyl monofunctional groups.

[0038] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0039] Example 1:

[0040] This embodiment provides a method for preparing a vinyl-functionalized COF composite membrane (TADA membrane), as detailed below:

[0041] (1) The polyacrylonitrile (PAN) substrate (50,000 molecular weight, 0.04 µm, purchased from Sanhe City Chuangzhiyuan Trading Company) was soaked in a solution of dopamine / tris-hydroxymethylaminomethane hydrochloride (tris-HCl, pH=8.5) with a concentration of 8 mg / mL. The substrate was shaken at a constant speed (3000 rpm) for 6 h at room temperature, washed with deionized water, and dried at 80℃ to obtain dopamine-modified PAN porous carrier (DPAN).

[0042] (2) Place the DPAN obtained in step (1) into a round-bottom flask, add 20 mL of isopropanol containing 0.2 mmol of 3-aminopropyltriethoxysilane (APTES), and heat in an oil bath at 50 °C for 3 h under a nitrogen atmosphere. Cool to room temperature, wash with isopropanol, and dry under vacuum at 60 °C. The aminated PAN porous support (APTES-DPAN) is obtained.

[0043] (3) Place the APTES-DPAN carrier in a 100 mL round-bottom flask, add 50 mL of 1,4-dioxane containing 50 mg of 2,5-divinyl terephthalaldehyde (DVA), heat at 60 °C for 4 h, cool to room temperature, wash several times with 1,4-dioxane and dry to obtain the DVA-DPAN carrier.

[0044] (4) Place DVA-DPAN at the bottom of a polytetrafluoroethylene-lined reactor. Dissolve 56 mg of tris(4-aminophenyl)amine (TAA) and 66.63 mg of DVA in 5 mL of a 4:1 mixture of 1,4-dioxane / trimethylbenzene, sonicate for 10 min, add 0.2 mL of 6 M acetic acid, sonicate for 20 min, add the mixture to the reactor, and heat at 120 °C for 3 days. Cool to room temperature, wash with 1,4-dioxane and ethanol, and vacuum dry at 60 °C to obtain the TADA membrane.

[0045] Example 2:

[0046] The TADA membrane prepared in Example 1 was combined with 100 mg of AIBN in a glass flask. Under a N2 atmosphere, 60 mL of 50% aqueous ethanol solution and 800 mg of sodium 2-mercaptoethanesulfonate were added. The mixture was reacted at 70 °C for 24 h. After washing with ethanol and drying, the TADA-SO3H membrane was obtained.

[0047] Example 3:

[0048] The TADA membrane prepared in Example 1 was combined with 100 mg of AIBN in a glass flask. 60 mL of methanol solution and 550 mg of cysteine ​​hydrochloride were added to the flask under N2 atmosphere. The mixture was reacted at 70°C for 24 h, washed with methanol, and dried to obtain the TADA-NH2 membrane.

[0049] Example 4:

[0050] The TADA membrane prepared in Example 1 was combined with 100 mg of AIBN in a glass flask. Under N2 atmosphere, 60 mL of THF solution and 450 mg of mercaptoacetic acid were added. The mixture was reacted at 60 °C for 12 h, washed with methanol, and dried to obtain the TADA-COOH membrane.

[0051] Test example:

[0052] 1. Figure 2 The images show SEM images of the cross-sections of DVA-DPAN, TADA, TADA-NH2, TADA-SO3H, TADA-COOH, and TADA-SO3H in the above embodiments. As can be seen from the images, the surfaces of the DVA-DPAN and TADA films are smooth. Furthermore, the films modified with different functional groups via click chemistry also have smooth surfaces without any obvious cracks or defects. The cross-sectional morphology of TADA-SO3H, which exhibits the best performance, was characterized, and its thickness was observed to be ~0.92 μm.

[0053] 2. Li + / Mg 2+ Separation performance testing: All performance tests were conducted in an H-type reaction tank, which consists of two identical compartments separated by a partition with an effective area of ​​1766 cm². 2 The membranes separate the compartments. Lithium hydroxide with a total concentration of 0.1 M is added to each compartment. + / Mg 2+ An aqueous solution and 25 mL of deionized water were used. During the test, the membrane front side faced the feed side. The feed solution and permeate were magnetically stirred (600 rpm) to avoid potential concentration polarization. The cation concentration in the solution was detected using inductively coupled plasma atomic emission spectrometry (ICP-AES). Data were recorded after the system reached steady state. The test was conducted at room temperature.

[0054] Ion permeability (J) i It can be calculated using the following formula:

[0055] (1)

[0056] Where V is the effective volume of the permeate solution, C is the permeate detection concentration obtained based on ICP detection, A is the effective area of ​​the membrane, and Δt is the permeation time.

[0057] Li + / Mg 2+ The separation factor can be calculated using the following formula:

[0058] (2)

[0059] Among them, C Mg2+ ,p (g·L -1 ) and C Li+ ,p (g·L -1 ) respectively refer to Mg in the permeate 2+ and Li + Concentration of C; Mg2+ ,f (g·L -1 ) and C Li+ ,f (g·L -1 These refer to the Mg in the feed liquid. 2+ and Li + The concentration.

[0060] The results are as follows Figure 3 As shown in the figure, the DVA molecule grafted onto the amino group of APTES only serves as a linker for further growth of the COF layer. It cannot fundamentally reduce the inherent pore size of the PAN substrate or affect ion transport behavior. The formation of the imine bond COF (TADA) makes the film more sensitive to Li + Exhibiting a certain degree of selectivity, after grafting characteristic functional groups, Li + / Mg 2+ The selectivity is significantly improved, and the selectivity of the TADA-SO3H membrane is superior to that of other membranes. Figure 3 (a) in the middle.

[0061] Using the method in Example 2, the effects of different grafting amounts of sodium 2-mercaptoethanesulfonate on Li were investigated. The grafting amount (0 mg, 400 mg, 800 mg, 1200 mg, and 1600 mg of sodium 2-mercaptoethanesulfonate were added) was controlled by adjusting the feed amount. + / Mg 2+ Effect of separation performance ( Figure 3 (b)). Among them, the TADA-SO3H (1.2 g) membrane exhibited the best Li. + / Mg 2+ Selectivity (24.3) and permeability (0.37 mol·m⁻¹) -2 ·h -1 ).

[0062] Comparative Example 1:

[0063] This comparative example does not employ click chemistry; instead, it uses a physical blending adsorption method between sulfonic acid groups and the TADA membrane. The specific steps are as follows:

[0064] The TADA membrane obtained in Example 1 was immersed in a 50% ethanol aqueous solution containing sodium 2-mercaptoethanesulfonate. Without adding AIBN initiator or heating, the mixture was stirred at room temperature for 24 hours. After washing and drying, the resulting product was subjected to Li…+ / Mg 2+ Separation performance test.

[0065] The results showed that the functional groups existed only through physical adsorption, exhibiting weak binding forces and easy elution; Li + Permeability: 0.54 mol·m -2 ·h -1 Li + / Mg 2+ Separation factor: 1.03. Therefore, physical blending cannot form stable covalent bonds on the pore surface, the pore chemical environment is uncontrollable, and the selectivity improvement is extremely low, far less than the effect of click chemical modification of covalent bonds.

[0066] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing click chemistry functionalized covalent organic frame membranes, characterized in that, Includes the following steps: S1. The polyacrylonitrile substrate was immersed in a dopamine / tris(hydroxymethyl)aminomethane hydrochloride buffer solution to react and obtain a dopamine-modified PAN porous support. S2. Under a protective atmosphere, the dopamine-modified PAN porous support obtained in step S1 is reacted with 3-aminopropyltriethoxysilane in the first solvent by heating to obtain an amino-modified PAN porous support. S3. The amino-modified PAN porous support is reacted with 2,5-divinyl terephthalaldehyde in a second solvent by heating to obtain a vinyl-functionalized support. S4. The vinyl-functionalized support obtained in step S3 is mixed with tris(4-aminophenyl)amine and 2,5-divinyl terephthalaldehyde in a third solvent and reacted under the action of acetic acid to obtain a vinyl-functionalized COF composite film. S5. Under a protective atmosphere, the vinyl-functionalized COF composite film obtained in step S4 is subjected to a click chemical reaction with the functionally modified monomer in a fourth solvent to obtain the click chemically functionalized covalent organic frame film; the functionally modified monomer is one or more of sodium 2-mercaptoethanesulfonate, cysteine ​​hydrochloride and mercaptoacetic acid.

2. The preparation method according to claim 1, characterized in that, In step S1, the concentration of dopamine in the dopamine / tris(hydroxymethyl)aminomethane hydrochloride buffer solution is 7.5 mg / mL to 8.5 mg / mL.

3. The preparation method according to claim 1, characterized in that, In step S2, the concentration of 3-aminopropyltriethoxysilane is 0.15 mmol to 0.25 mmol.

4. The preparation method according to claim 1, characterized in that, In step S2, the first solvent is isopropanol and / or ethanol.

5. The preparation method according to claim 1, characterized in that, In step S3, the concentration of 2,5-divinyl terephthalaldehyde is 0.9 mg / mL to 1.1 mg / mL.

6. The preparation method according to claim 1, characterized in that, In step S3, the second solvent is 1,4-dioxane; And / or, the conditions for the heating reaction are: heating at 60℃-65℃ for 4 h-4.5 h.

7. The preparation method according to claim 1, characterized in that, In step S4, the ratio of the total mass of the tris(4-aminophenyl)amine and 2,5-divinyl terephthalaldehyde to the surface area of ​​the vinyl-functionalized support is 12 mg / cm². -2 -13 mg / cm -2 ; And / or, the third solvent is 1,4-dioxane and mesitylene.

8. The preparation method according to claim 1, characterized in that, The fourth solvent is selected from one or more of aqueous ethanol, methanol, and tetrahydrofuran; And / or, the conditions for the click chemical reaction are: 60℃-70℃ for 12 h-24 h.

9. The click chemistry functionalized covalent organic frame membrane obtained by the preparation method according to any one of claims 1-8.

10. The click chemistry functionalized covalent organic frame membrane according to claim 9 in Li + / Mg 2+ Applications in separation.

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