Preparation and application of anionic covalent organic framework film material

Abstract

The invention discloses preparation and application of an anionic covalent organic framework film material, and belongs to the field of preparation of environment-friendly separation materials. Comprising the following steps: 1, soaking an AAO support body in deionized water for 1 hour at room temperature; 2, taking out the soaked AAO support body, and airing; 3, accurately weighing two construction monomers, namely 2, 5-diaminobenzene sulfonic acid and 2, 4, 6-trihydroxy-1, 3, 5-benzenetricarboxaldehyde, adding a mixed solvent, namely dimethyl sulfoxide and N-methyl pyrrolidone, and carrying out ultrasonic treatment for 15 minutes, so that the two monomer powders are completely dissolved to form a homogeneous solution; 4, placing an AAO substrate at the bottom of the reaction solution, and carrying out a hydrothermal reaction; 5, fishing out the AAO substrate to obtain a COF film with complete morphology; 6, acetone and absolute ethyl alcohol are sequentially used for washing, standing is conducted at the room temperature, and the TpPa-SO3H / AAO nano-porous membrane is obtained. The thin film material provided by the invention has high crystallinity and good stability, and shows efficient metal ion selectivity, and the separation factor of Li < + > / Mg < 2 + > is as high as 15 in a two-component mixed system of LiCl and MgCl2.

Description

Technical Field

[0001] The present application belongs to the field of preparation of environmentally friendly membrane separation materials, and more specifically, it relates to the preparation and application of an anionic covalent organic framework thin film material. Background Art

[0002] Lithium is a critical energy metal. With the rapid development of the lithium battery industry in recent years, the development and extraction of lithium resources has become a key area of ​​research. China's lithium resources are primarily found in the brine of salt lakes on the Qinghai-Tibet Plateau. However, the high ratio of magnesium to lithium hinders the extraction and separation of lithium ions. Therefore, the development of highly selective lithium-magnesium separation technology from salt lake brines is urgent. Currently used methods for lithium extraction from salt lake brines include calcination, extraction, and electrochemical methods, but these methods still present numerous challenges, including equipment corrosion, environmental pollution, and high costs.

[0003] Membrane separation technology is a widely used process for ion separation. Compared with traditional distillation, concentration, or adsorption techniques, it offers numerous advantages, including high separation efficiency, low energy consumption, and environmental friendliness. Traditional separation membranes consist of polymeric or ceramic membranes. However, due to the lack of a continuous, regular pore structure and the difficulty in adjusting the pore environment, membrane materials exhibit low permeability and selectivity. Covalent organic frameworks (COFs) are a new type of crystalline porous material. Through the self-assembly of molecular-level building blocks, novel porous materials with highly tunable pore order, high specific surface area, and high stability can be obtained. The long-range order and porosity of their internal pores, in particular, make COFs promising applications in membrane separations and have attracted increasing attention. Sun et al. constructed a series of two-dimensional COF membranes containing oligoether chains of varying lengths. Experimental results for lithium-magnesium ion separation showed that the resulting membranes exhibited a Li+ / Mg2+ separation factor of up to 64. The lithiophilic nature of the oligoether chains facilitates the migration of Li+ within the membrane pores, enabling efficient separation of lithium and magnesium ions. Wen et al. prepared a COF-300 / PS mixed matrix membrane. Leveraging the interaction between -NH2 groups and magnesium ions within the material, the membrane enhanced the migration of magnesium ions within the pores, ultimately achieving a Mg2+ / Li+ selectivity of 14.7. Hou et al. prepared COF-EBxBDy on a polyacrylonitrile substrate. By adjusting the ratio of ethidium bromide (EB) and benzidine (BD), the COF nanochannels produced varying charge densities, leading to varying electrostatic repulsions or attractions for the lithium and magnesium ions being separated, thus affecting the transport properties of the lithium and magnesium ions within the channels. The resulting COF-EB1BD1 / PAN exhibited a Li+ / Mg2+ selectivity of up to 500 under electrodialysis conditions. Therefore, by introducing functional groups into COF materials, the material can effectively separate molecules of similar molecular weight but different electronegativities based on the pore size screening effect, electrostatic interactions, and pore-ion interactions within the charged pores. Ultimately, the material exhibits excellent selectivity for the separation of monovalent and polyvalent metal ions, possessing significant practical value and promising application prospects. Summary of the Invention

[0004] The present invention aims to provide a method for producing a covalent organic framework thin film material with single and multivalent metal ion separation performance. The method is simple and easy to implement, highly versatile, and the resulting material has high crystallinity and good stability, and can achieve effective separation of two metal ions in a lithium-magnesium ion mixture system.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A solvothermal synthesis method of a covalent organic framework thin film material having monovalent and polyvalent metal ion separation performance comprises the following steps:

[0007] 1) At room temperature, soak a 120-160 nm porous AAO substrate in a PEI aqueous solution for 1 hour and then air dry.

[0008] 2) Accurately weigh 2,5-diaminobenzenesulfonic acid (DABA, 8.0 mg, 0.04 mmol) and 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde (Tp, 12.0 mg, 0.05 mmol) and add them separately to a 50 mL beaker;

[0009] 3) Add 4 ml of DMSO and 4 ml of NMP to the reaction system in step 2, and sonicate for 15 minutes to completely dissolve the two monomer powders to form a homogeneous solution;

[0010] 4) placing the AAO substrate obtained in step 1 into the solution system of step 3, so that the solution completely covers the surface of the substrate;

[0011] 5) Place the reaction system from step 4 in a 60°C oven and heat for 12 hours;

[0012] 6) Use a film scoop to remove the AAO substrate from the reaction system in step 5 to obtain a thin film material covered with an orange-red film.

[0013] 7) The membrane material obtained in step 6 was washed with acetone and anhydrous ethanol in sequence and allowed to stand at room temperature to obtain a TpPa-SO3H / AAO nanoporous membrane.

[0014] In the step 1), the amount of deionized water used is 6 ml per millimole of polyethyleneimine (PEI).

[0015] In step 2), the molar ratio of 2,5-diaminobenzenesulfonic acid (DABA, 8.0 mg, 0.04 mmol) to 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde is 4:5.

[0016] In step 3), the amounts of DMSO and 4 ml of NMP are equal, both 4 ml.

[0017] In step 5), the hydrothermal reaction temperature is 60° C. and the reaction time is 12 h.

[0018] The anionic covalent organic framework film material prepared above can be fixed in the middle of a homemade U-shaped diffusion dialysis device. The salt solution to be tested and deionized water are added to the feed liquid chamber and the receiving chamber respectively. Under stirring conditions, the conductivity change of the receiving chamber is continuously recorded, and the concentration of the receiving chamber is detected by inductively coupled plasma atomic emission spectrometry to separate the target ions.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The preparation method of the TpPa-SO3H / AAO membrane material of the present invention is very simple and easy. The obtained material can be used as a membrane separation material for solutions containing monovalent and polyvalent mixed metal ions, providing some new ideas for the effective separation of lithium and magnesium ions in salt lake brine;

[0021] 2. The TpPa-SO3H / AAO membrane material prepared by the present invention has an average COF membrane thickness of approximately 1.1 μm, tightly bonded to the substrate, and facilitates the transport and separation of metal ions in the pores;

[0022] 3. The TpPa-SO3H / AAO membrane material prepared in this invention exhibits a strong negative charge. The negatively charged pore environment facilitates the entry and further migration of metal cations to be separated, thereby improving the membrane's selectivity and flux. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Structure (a) and pore structure diagram (b) of TpPa-SO3H;

[0024] Figure 2 SEM diagrams of the front (a), back (b) and cross-section (c) of the TpPa-SO3H / AAO nanoporous membrane;

[0025] Figure 3 Variation of zeta potential of TpPa-SO3H membrane with pH

[0026] Figure 4 Changes in electrical conductivity over time during different ion diffusion processes in AAO porous substrate and TpPa-SO3H / AAO nanoporous membrane (a); Comparison of the permeation rates of lithium and magnesium ions in different separation substrate systems (b); Separation effect of TpPa-SO3H / AAO nanoporous membrane on single-component systems of LiCl (0.1 mol / L) or MgCl2 (0.1 mol / L) (c); Separation effect of TpPa-SO3H / AAO porous membrane on mixed ion systems (0.1 M LiCl and 0.1 M MgCl2) (d). DETAILED DESCRIPTION

[0027] The following further describes the solvothermal synthesis method and metal ion separation effect of an anionic covalent organic framework thin film material with single and multivalent metal ion separation performance according to the present invention through specific examples. It should also be noted that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0028] Example 1

[0029] The specific process steps of a solvothermal synthesis method of anionic covalent organic framework thin film materials are as follows:

[0030] (1) Soak the 160-200 nm AAO support in a PEI aqueous solution at room temperature for 1 hour. Remove the soaked AAO support and air dry it.

[0031] (2) Accurately weigh 2,5-diaminobenzenesulfonic acid (DABA, 8.0 mg, 0.04 mmol) and 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde (Tp, 12.0 mg, 0.05 mmol) and add them separately into a 50 mL beaker;

[0032] (3) Add 4 ml of DMSO and 4 ml of NMP to the reaction system in step 2, and sonicate for 15 minutes to completely dissolve the two monomer powders to form a homogeneous solution;

[0033] (4) placing the AAO substrate obtained in step 1 into the solution system of step 3 so that the solution completely covers the surface of the substrate;

[0034] (5) Place the reaction system in step 4 in a 60°C oven and heat the reaction for 12 hours;

[0035] (6) Using a film scooping device, the AAO substrate is scooped out from the reaction system in step 5 to obtain a thin film material covered with an orange-red film;

[0036] (7) The membrane material obtained in step 6 was washed with acetone and anhydrous ethanol in sequence and allowed to stand at room temperature to obtain a TpPa-SO3H / AAO nanoporous membrane, such as Figure 1 and Figure 2 shown.

[0037] Example 2

[0038] Lithium-magnesium separation performance test of TpPa-SO3H / AAO membrane material prepared in Example 1

[0039] Based on the static ion diffusion experiment, the transport and separation effects of ions in the nanoporous membrane were characterized. First, the membrane was fixed in the middle of a self-made U-shaped diffusion dialysis device with a test area of ​​3.14 cm 2 . The two sides of the membrane are the feed and liquid chambers and the receiving chambers respectively. During the test, 50 mL and 0.1 mol / L of the salt solution to be tested (LiCl, MgCl2 or a mixed solution of LiCl and MgCl2) and deionized water were added to the feed and liquid chambers and the receiving chambers respectively, and continuous stirring was carried out throughout the process to eliminate concentration polarization. The conductivity change of the receiving chamber was continuously recorded using a conductivity meter, and the ion concentration was calculated based on the standard curve. For the binary mixed ion diffusion system, the ion concentration in the receiving chamber was detected by inductively coupled plasma atomic emission spectrometry.

[0040] After 3 hours of diffusion, the conductivity in the diffusion chamber reached 222 (LiCl) and 15.0 (MgCl2) μS cm -1 ( Figure 4 a), the corresponding ion diffusion rate is 0.1552 (Li + ) and 0.0065 (Mg 2+ ) mol m -2 ·h -1 ( Figure 4 b). According to the ratio of the diffusion rates of the single components, the ideal Li + / Mg 2+ The selectivity is 24.00 ( Figure 4 c).

[0041] For the binary mixed solution system consisting of LiCl (0.1 mol / L) and MgCl2 (0.1 mol / L), Li + / Mg 2+ The separation factor reaches a maximum of 22.00 at 90 min and then stabilizes at around 15.00 as time goes by ( Figure 4 d), which is basically consistent with the ideal selectivity obtained by single-component solution.

[0042] Comparative Example:

[0043] Instead of using the TpPa-SO3H / AAO membrane material prepared in Example 1, only the AAO porous substrate was used. In the separation selectivity experiment of the single-component system of LiCl (0.1 mol / L) or MgCl2 (0.1 mol / L), it was found that the conductivity in the diffusion chamber reached 575 (LiCl) and 795 (MgCl2) μS cm after 3 h of diffusion, respectively. -1 , the corresponding ion diffusion rates are 0.4019 (Li + ) and 0.3417 (Mg 2+ ) mol m -2 ·h -1 ( Figure 4 a). The results show that there is no significant difference in the diffusion rates of the two ions, proving that the AAO substrate has no obvious selective separation effect on the two.

Claims

1. A method for preparing anionic covalent organic framework thin film material, characterized by: The steps include: 1) Soak a 120-160 nm porous AAO substrate in deionized water for 1 hour at room temperature and then air dry. 2) Accurately weigh 2,5-diaminobenzenesulfonic acid (DABA, 8.0 mg, 0.04 mmol) and 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde (Tp, 12.0 mg, 0.05 mmol) and add them separately to a 50 mL beaker; 3) Add DMSO and NMP to the reaction system in step 2, respectively, and sonicate for 15 minutes to completely dissolve the two monomer powders to form a homogeneous solution; 4) placing the AAO substrate obtained in step 1 into the solution system of step 3, so that the solution completely covers the surface of the substrate; 5) placing the reaction system of step 4 in an oven for hydrothermal reaction; 6) Using a film scooping device, remove the AAO substrate from the reaction system in step 5 to obtain a thin film material; 7) The membrane material obtained in step 6 was washed with acetone and anhydrous ethanol in sequence and allowed to stand at room temperature to obtain a TpPa-SO3H / AAO nanoporous membrane.

2. The preparation method according to claim 1, wherein: In the step 1), the amount of deionized water used is 6 ml per millimole of polyethyleneimine (PEI).

3. The preparation method according to claim 1, wherein: In the step 2), the molar ratio of the added 2,5-diaminobenzenesulfonic acid (DABA, 8.0 mg, 0.04 mmol) to 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde is 4:

5.

4. The preparation method according to claim 1, wherein: In the step 3), the amount of DMSO and NMP is 1:

1.

5. The preparation method according to claim 1, wherein: In the step 4), the hydrothermal reaction temperature is 60° C. and the reaction time is 12 h.

6. The preparation method according to claim 1, wherein: The thin film material obtained in step 6) is a thin film material covered with an orange-red film.

7. An application of an anionic covalent organic framework film material in a lithium-magnesium ion mixed system. The anionic covalent organic framework film material prepared above is fixed in the middle of a homemade U-shaped diffusion dialysis device. The salt solution to be tested and deionized water are added to the feed liquid chamber and receiving chamber, respectively. Under stirring conditions, the conductivity change of the receiving chamber is continuously recorded, and the concentration in the receiving chamber is detected by inductively coupled plasma atomic emission spectrometry to separate the target ions.

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