Preparation method of ionic liquid covalent organic framework hybrid material and its application in adsorption and separation of rare earth ions

Abstract

The present invention discloses a method for preparing an ionic liquid covalent organic framework hybrid material and its application in adsorption and separation of rare earth ions, belonging to the field of environmental protection technology. The present invention prepares a sulfonic acid functionalized covalent organic framework by Schiff base reaction of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde and 2,5-diaminobenzenesulfonic acid; then the sulfonic acid functionalized covalent organic framework is hybridized with ionic liquid 1-carboxymethyl-3-methylimidazolium chloride using an ion exchange method to obtain an ionic liquid covalent organic framework hybrid material, which solves the problem of dissolution loss of ionic liquid in aqueous phase and improves the adsorption performance of the material for rare earth ions. The ionic liquid covalent organic framework hybrid material prepared by the present invention has a simple preparation method, high crystallinity, and excellent adsorption and separation performance for rare earth ions, and can be used as an efficient adsorbent for low-concentration rare earth tail water.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental protection, and in particular relates to a preparation method of an ionic liquid covalent organic framework hybrid material and an application thereof in adsorbing and separating rare earth ions. Background Art

[0002] Ionic liquids (ILs) are a class of room-temperature molten salts composed primarily of organic cations or inorganic or organic anions. They typically exhibit high thermal, chemical, and electrochemical stability. Because their vapor pressure is negligible and they are virtually non-flammable, ILs are known as "green solvents." Furthermore, their structure is tunable, meaning their properties can be diversified by adjusting the functional groups or structure of the cations or anions. The unique physicochemical properties of ILs have garnered widespread attention in the field of rare earth ion separation and purification based on liquid-liquid extraction. However, during the liquid-liquid extraction process, some anions or cations of some ILs transfer to the aqueous phase, resulting in the loss of the ionic liquid. Some ionic liquids are even miscible with water, making extraction operations difficult.

[0003] Covalent organic frameworks (COFs) are a class of two- or three-dimensional porous materials composed of lightweight elements such as C, H, O, and N, connected by stable covalent bonds. COFs are ideal solid-phase loading materials due to their regular pore structure, large specific surface area, adjustable functional groups, and high chemical stability. By utilizing COFs to load ionic liquids into a solid matrix, the likelihood of ionic liquids entering the aqueous phase is reduced to a certain extent, potentially resolving the aforementioned problem of ionic liquid dissolution in the aqueous phase. Furthermore, to date, there have been no reports on the use of hybrid materials containing covalent organic frameworks loaded with ionic liquids for the adsorption and separation of rare earth ions. Summary of the Invention

[0004] The present invention aims to provide a method for preparing an ionic liquid covalent organic framework hybrid material and its application in the adsorption and separation of rare earth ions. This method utilizes a Schiff base reaction between 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde and 2,5-diaminobenzenesulfonic acid to synthesize a sulfonic acid-functionalized covalent organic framework (COF-SO3H). Subsequently, an ionic liquid is loaded onto the covalent organic framework via ion exchange to prepare an ionic liquid covalent organic framework hybrid material (COF-SO3H-IL). This hybrid material not only solves the solubility problem of the ionic liquid 1-carboxymethyl-3-methylimidazolium chloride in aqueous phases but also improves the material's adsorption performance for rare earth ions, providing a new strategy for the efficient utilization of rare earth resources.

[0005] The present invention prepares a sulfonic acid functionalized covalent organic framework COF-SO3H through the Schiff base reaction between 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde (Tp) and 2,5-diaminobenzenesulfonic acid (Pa-SO3H). Subsequently, the sulfonic acid functionalized covalent organic framework is compounded with the ionic liquid 1-carboxymethyl-3-methylimidazolium chloride by an ion exchange method to obtain the ionic liquid covalent organic framework hybrid material COF-SO3H-IL. Through the hybridization of the ionic liquid, carboxyl functional groups with strong affinity for rare earth ions are introduced into COF-SO3H-IL. At the same time, the larger size of the ionic liquid further reduces the pore size of COF-SO3H, and can construct more effective rare earth ion capture nanochannels in the material, greatly improving the material's affinity for a variety of rare earth ions including La. 3+ 、Ce 3+ 、Pr 3+ 、Nd 3+ 、Sm 3+ 、Eu 3+ 、Gd 3+ 、Tb 3+ 、Dy 3+ 、Ho 3+ 、Er 3+ 、Tm 3+ 、Yb 3+ 、Lu 3 + 、Y 3+ The present invention not only solves the problem of dissolution loss of ionic liquid 1-carboxymethyl-3-methylimidazolium chloride in water phase, but also improves the adsorption performance of the material for rare earth ions.

[0006] The present invention provides a method for preparing an ionic liquid covalent organic framework hybrid material, comprising:

[0007] The sulfonic acid functionalized covalent organic framework and the ionic liquid 1-carboxymethyl-3-methylimidazolium chloride were treated by ion exchange to obtain an ionic liquid covalent organic framework hybrid material;

[0008] The sulfonic acid functionalized covalent organic framework is prepared by using 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde and 2,5-diaminobenzenesulfonic acid as raw materials through a Schiff base reaction.

[0009] Furthermore, the preparation method of the ionic liquid covalent organic framework hybrid material includes:

[0010] 1) Mixing the ionic liquid 1-carboxymethyl-3-methylimidazolium chloride dispersed in isopropanol with potassium hydroxide dispersed in isopropanol and stirring at room temperature;

[0011] 2) The mixed solution is centrifuged at high speed to obtain a clear upper layer of liquid;

[0012] 3) The upper clear liquid and the sulfonic acid functionalized covalent organic framework are stirred at room temperature until the solution becomes neutral.

[0013] Furthermore, in step 1), the mass ratio of the ionic liquid 1-carboxymethyl-3-methylimidazolium chloride to potassium hydroxide is 1:(1.0-2.5); and the stirring time at room temperature is 12-24 h.

[0014] Furthermore, in step 2), the centrifugation time is 5-15 min, and the centrifugal speed is 5000-10000 rpm.

[0015] Furthermore, the preparation method of the sulfonic acid functionalized covalent organic framework includes:

[0016] 1) 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde and 2,5-diaminobenzenesulfonic acid are used as raw materials, a solvent is added, mixed, and ultrasonicated to obtain a reaction solution;

[0017] 2) The resulting reaction solution is degassed through a freeze-thaw cycle, flame-sealed, and heated at 100-200°C for 1-5 days. The precipitate is collected, washed, and dried to obtain a sulfonic acid-functionalized covalent organic framework.

[0018] Furthermore, in step 1), the amount ratio of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde to 2,5-diaminobenzenesulfonic acid is 1:(1-2).

[0019] Furthermore, in step 1), the solvent is composed of o-dichlorobenzene, n-butanol and acetic acid in a volume ratio of (1-5):(5-15):1; the concentration of the acetic acid is 6 M.

[0020] The present invention also provides the use of the ionic liquid covalent organic framework hybrid material obtained by the preparation method in the adsorption and separation of rare earth ions.

[0021] Furthermore, the rare earth ion is La 3+ 、Ce 3+ 、Pr 3+ 、Nd 3+ 、Sm 3+ 、Eu 3+ 、Gd 3+ 、Tb 3+ 、Dy 3+ 、Ho 3+ 、Er 3 + 、Tm 3+ 、Yb 3+ 、Lu 3+ 、Y 3+At least one of .

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The ionic liquid covalent organic framework hybrid material prepared by the present invention has high crystallinity and a simple preparation method.

[0024] (2) The ionic liquid covalent organic framework hybrid material prepared by the present invention solves the problem that the ionic liquid 1-carboxymethyl-3-methylimidazolium chloride is miscible with water and is difficult to be used for the extraction and separation of rare earth elements in the aqueous phase.

[0025] (3) The ionic liquid covalent organic framework hybrid material prepared by the present invention introduces a carboxyl functional group with a strong affinity for rare earth ions.

[0026] (4) The ionic liquid covalent organic framework hybrid material prepared by the present invention can reduce the pore size of the COFs material due to the introduction of large-sized cations in the ionic liquid, and construct efficient rare earth ion capture nanochannels inside the material.

[0027] (5) The ionic liquid covalent organic framework hybrid material prepared by the present invention improves the adsorption performance of COFs materials for rare earth elements and is expected to be used as an efficient adsorbent for low-concentration rare earth tail water. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the preparation process of COF-SO3H.

[0029] Figure 2 These are the experimental test PXRD patterns of Tp, Pa-SO3H and COF-SO3H.

[0030] Figure 3 These are the infrared spectra of Tp, Pa-SO3H and COF-SO3H.

[0031] Figure 4 Schematic diagram of the preparation process of COF-SO3H-IL.

[0032] Figure 5 This is the distribution coefficient diagram of COF-SO3H, COF-SO3H-IL, and COF-SO3H-IL(MC) for rare earth ions. DETAILED DESCRIPTION

[0033] To make the objects, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be described clearly and completely below in conjunction with the examples. Where specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0035] Example 1: Preparation and characterization of sulfonated covalent organic frameworks

[0036] Figure 1 This is a schematic diagram of the preparation process of COF-SO3H. Figure 1 It can be seen that 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde (Tp, 21 mg), 2,5-diaminobenzenesulfonic acid (Pa-SO3H, 28.2 mg), o-dichlorobenzene (0.30 mL) and n-butanol (0.70 mL) were charged into a Pyrex tube and ultrasonicated for 10 minutes. Then, 6 M acetic acid solution (0.10 mL) was added to obtain a reaction mixture. The Pyrex tube containing the reaction mixture was degassed through three freeze-pump-thaw cycles, flame-sealed and heated in an oven at 120°C for 3 days. After cooling, it was filtered and the obtained white solid product was washed three times with deionized water, N,N-dimethylformamide (DMF) and acetone. The solid was collected and dried in vacuum at 80°C for 12 hours to obtain a sulfonated covalent organic framework (COF-SO3H). Figure 2 The experimental test PXRD patterns of Tp, Pa-SO3H and COF-SO3H are shown in Figure 1. Figure 2 It can be seen that the crystallinity of COF-SO3H was characterized by powder X-ray diffraction and it was found that the diffraction peaks of the material at 4.6°, 8.0°, and 26.5° correspond to the 100, 110, and 001 crystal planes of the material, respectively, indicating that the solvent thermal reaction is complete and the synthesized COF-SO3H has good crystallinity.

[0037] Figure 3 The infrared spectra of Tp, Pa-SO3H and COF-SO3H are shown in Figure 2. Figure 3 It can be seen that the NH stretching vibration peak (3335-3426 cm -1 ) and the stretching vibration peak of the aldehyde group in the monomer Tp (1646 cm -1 ) completely disappeared in the product COF-SO3H, indicating that the monomers have been completely reacted during the material synthesis process. In addition, the disappearance of the C=N double bond stretching peak and the new peak at 1583 cm -1 The appearance of the C=C double bond at 1437 cm indicates that the material has undergone a structural transformation from enol to keto. -1The CN single bond peak formed by enol-keto tautomerism is located at 1237 cm -1 In COF-SO3H, the wavelength is located at 1026 cm -1 The peak at is the S-OH stretching vibration peak of the -SO3H group in the material.

[0038] Example 2: Preparation and characterization of ionic liquid covalent organic framework hybrid materials

[0039] Figure 4 This is a schematic diagram of the preparation process of COF-SO3H-IL. Figure 4 As shown, 0.15 mmol of the ionic liquid 1-carboxymethyl-3-methylimidazolium chloride was thoroughly dispersed in 20 mL of isopropanol. Separately, 0.3 mmol of potassium hydroxide was thoroughly dispersed in 10 mL of isopropanol. When the ionic liquid and the isopropanol solution of potassium hydroxide were mixed, the originally clear solution quickly became turbid, indicating that an acid-base neutralization reaction occurred between the ionic liquid and potassium hydroxide, generating the product potassium chloride. The mixed solution was further stirred at room temperature for 12 hours to ensure complete reaction.

[0040] The mixed solution after the complete reaction was centrifuged at 8000 rpm for 10 minutes to remove the insoluble potassium chloride. The clear upper layer, an isopropanol solution of the product 1-carboxymethyl-3-methylimidazolium hydroxide, was then added to 0.05 mmol of COF-SO₃H₄ using an ion exchange method. The mixture was stirred at room temperature for 12 hours. The acid-base neutralization reaction allowed the hydroxide ions in the ionic liquid to react with the protons in COF-SO₃H₄, exchanging the 1-carboxymethyl-3-methylimidazolium cations for the protons in COF-SO₃H₄. This yielded the ionic liquid covalent organic framework hybrid material COF-SO₃H-IL. The color of the product changed from the brick-red color of COF-SO₃H₄ to the brown color of COF-SO₃H-IL.

[0041] In addition, in order to further demonstrate the necessity and effectiveness of the ion exchange method for preparing ionic liquid covalent organic framework hybrid materials (COF-SO3H-IL) in this article, the ionic liquid 1-carboxymethyl-3-methylimidazolium chloride and the covalent organic framework COF-SO3H were ground in a mortar to obtain a physical mixture of ionic liquid and covalent organic framework (COF-SO3H-IL(MC)) for comparison.

[0042] Example 3: Application of ionic liquid covalent organic framework hybrid materials for adsorption and separation of rare earth ions

[0043] COF-SO3H, COF-SO3H-IL prepared by ion exchange method, and COF-SO3H-IL(MC) prepared by mechanical grinding method were used as adsorbents for the adsorption of rare earth ions (La 3+ 、Ce 3+ 、Pr 3+ 、Nd 3+ 、Sm 3+ 、Eu 3+ 、Gd 3+ 、Tb 3+ 、Dy 3+ 、Ho 3 + 、Er 3+ 、Tm 3+ 、Yb 3+ 、Lu 3+ 、Y 3+ ) were investigated for their adsorption and separation properties. 5 mg of COF-SO3H, COF-SO3H-IL, and COF-SO3H-IL(MC) were added to 10 mL of a rare earth mixture, stirred for 12 hours, and filtered through a 0.22 μm microporous membrane. The rare earth ion content in the filtrate was measured using inductively coupled plasma optical emission spectrometry. The partition coefficients of COF-SO3H, COF-SO3H-IL, and COF-SO3H-IL(MC) for rare earth ions were calculated, respectively, to investigate the materials' affinity for rare earth ions. Figure 5 are the distribution coefficients of COF-SO3H, COF-SO3H-IL and COF-SO3H-IL(MC) for rare earth ions. Figure 5 It can be seen that COF-SO3H-IL prepared by ion exchange method has a better performance in the treatment of 15 rare earth ions (La 3+ 、Ce 3+ 、Pr 3+ 、Nd 3+ 、Sm 3+ 、Eu 3+ 、Gd 3+ 、Tb 3+ 、Dy 3+ 、Ho 3+ 、Er 3+ 、Tm 3+ 、Yb 3+ 、Lu 3+ 、Y 3+) have the highest distribution coefficient. This is mainly attributed to the fact that COF-SO3H-IL introduces ionic liquids through ion exchange. The ionic liquids have carboxyl functional groups with strong affinity for rare earth ions. At the same time, the introduction of larger cations in the ionic liquids further reduces the pore size of COF-SO3H, enabling the construction of more effective rare earth ion capture nanochannels in the material, greatly improving the material's affinity for a variety of rare earth ions, including La. 3+ 、Ce 3+ 、Pr 3+ 、Nd 3+ 、Sm 3+ 、Eu 3+ 、Gd 3+ 、Tb 3+ 、Dy 3+ 、Ho 3+ 、Er 3+ 、Tm 3+ 、Yb 3+ 、Lu 3+ 、Y 3+ In addition, through Figure 5 It can be seen that the adsorption performance of COF-SO3H-IL(MC) for all rare earth ions is lower than that of COF-SO3H-IL and COF-SO3H. This is mainly due to the fact that the material prepared by mechanical grinding cannot effectively load the ionic liquid into the solid phase matrix COFs material. The ionic liquid dissolves when interacting with the aqueous phase, resulting in the inability to transfer rare earth ions from the aqueous phase to the solid phase, causing the adsorption performance of COF-SO3H-IL(MC) for rare earth ions to decrease. This further proves the necessity and effectiveness of the ionic liquid covalent organic framework hybrid material prepared by the ion exchange method of the present invention.

[0044] The embodiments described above merely represent several preferred embodiments of the present invention. While the descriptions are relatively specific and detailed, they are not intended to limit the present invention. It should be noted that those skilled in the art will readily appreciate that the present invention is susceptible to various variations and modifications. Any modifications, equivalent substitutions, or improvements within the scope of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for preparing an ionic liquid covalent organic framework hybrid material, characterized in that: include: The sulfonic acid functionalized covalent organic framework and the ionic liquid 1-carboxymethyl-3-methylimidazolium chloride were treated by ion exchange to obtain an ionic liquid covalent organic framework hybrid material; The sulfonic acid functionalized covalent organic framework is prepared by using 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde and 2,5-diaminobenzenesulfonic acid as raw materials through a Schiff base reaction.

2. The method for preparing the ionic liquid covalent organic framework hybrid material according to claim 1, characterized in that: The preparation method of the ionic liquid covalent organic framework hybrid material comprises: 1) Mixing the ionic liquid 1-carboxymethyl-3-methylimidazolium chloride dispersed in isopropanol with potassium hydroxide dispersed in isopropanol and stirring at room temperature; 2) The mixed solution is centrifuged at high speed to obtain a clear upper layer of liquid; 3) The upper clear liquid and the sulfonic acid functionalized covalent organic framework are stirred at room temperature until the solution becomes neutral.

3. The method for preparing the ionic liquid covalent organic framework hybrid material according to claim 2, characterized in that: Step 1) The mass ratio of the ionic liquid 1-carboxymethyl-3-methylimidazolium chloride to potassium hydroxide is 1:(1.0-2.5); and the stirring time at room temperature is 12-24 h.

4. The method for preparing the ionic liquid covalent organic framework hybrid material according to claim 2, characterized in that: Step 2) The centrifugation time is 5-15 min, and the centrifugal speed is 5000-10000 rpm.

5. The method for preparing the ionic liquid covalent organic framework hybrid material according to claim 1, characterized in that: The preparation method of the sulfonic acid functionalized covalent organic framework comprises: 1) 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde and 2,5-diaminobenzenesulfonic acid are used as raw materials, a solvent is added, mixed, and ultrasonicated to obtain a reaction solution; 2) The resulting reaction solution is degassed through a freeze-thaw cycle, flame-sealed, and heated at 100-200°C for 1-5 days. The precipitate is collected, washed, and dried to obtain a sulfonic acid-functionalized covalent organic framework.

6. The method for preparing the ionic liquid covalent organic framework hybrid material according to claim 5, characterized in that: In step 1), the mass ratio of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde to 2,5-diaminobenzenesulfonic acid is 1:(1-2).

7. The method for preparing the ionic liquid covalent organic framework hybrid material according to claim 5, characterized in that: Step 1) The solvent is composed of o-dichlorobenzene, n-butanol and acetic acid in a volume ratio of (1-5):(5-15):1; the acetic acid concentration is 6M.

8. The ionic liquid covalent organic framework hybrid material obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the ionic liquid covalent organic framework hybrid material obtained by the preparation method according to any one of claims 1 to 7 in the adsorption and separation of rare earth ions.

10. The use according to claim 9, characterized in that: The rare earth ion is La 3+ 、Ce 3+ 、Pr 3+ 、Nd 3+ 、Sm 3+ 、Eu 3+ 、Gd 3+ 、Tb 3+ 、Dy 3+ 、Ho 3+ 、Er 3+ 、Tm 3+ 、Yb 3+ 、Lu 3+ 、Y 3+ At least one of .

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