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

Abstract

The invention discloses a preparation method of an ionic liquid covalent organic framework hybrid material and application of the ionic liquid covalent organic framework hybrid material to adsorption and separation of rare earth ions, and belongs to the technical field of environmental protection. The preparation method comprises the following steps: carrying out a Schiff base reaction on 2, 4, 6-trihydroxy-1, 3, 5-benzenetricarboxaldehyde and 2, 5-diaminobenzene sulfonic acid to prepare a sulfonic acid functionalized covalent organic framework; then the sulfonic acid functionalized covalent organic framework is hybridized with ionic liquid 1-carboxymethyl-3-methylimidazolium chloride by using an ion exchange method to obtain the ionic liquid covalent organic framework hybrid material, so that the problem of solution loss of the ionic liquid in a water phase is solved, and meanwhile, the adsorption performance of the material on rare earth ions is improved. The ionic liquid covalent organic framework hybrid material prepared by the invention is simple in preparation method and high in crystallinity, has excellent adsorption and separation performance on rare earth ions, and can be used as an efficient adsorbent for low-concentration rare earth tail water.

Description

Technical Field

[0001] The 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 mainly composed of organic cations or inorganic or organic anions, which usually have high thermal stability, chemical stability and electrochemical stability. Since the vapor pressure of ionic liquids is negligible and they are almost non-flammable, ionic liquids are called "green solvents". In addition, the structure of ionic liquids is adjustable, that is, the properties can be diversified by adjusting the functional groups or structures of cations or anions. The unique physicochemical properties of ionic liquids have attracted widespread attention in the field of rare earth ion separation and purification based on liquid-liquid extraction. However, during the liquid-liquid extraction process of some ionic liquids, some anions or cations will be transferred to the aqueous phase, resulting in the loss of ionic liquids, and even some ionic liquids themselves are miscible with water, making the extraction operation difficult.

[0003] Covalent Organic Frameworks (COFs) are a class of two-dimensional or three-dimensional porous materials composed of lightweight elements such as C, H, O, and N, connected by stable covalent bonds. COFs materials are an ideal solid-phase loading material due to their regular pore structure, large specific surface area, adjustable functional groups, and high chemical stability. By using COFs materials to load ionic liquids in a solid matrix, the possibility of ionic liquids entering the aqueous phase will be reduced to a certain extent, which is expected to solve the problem of dissolution of the above-mentioned ionic liquids in the aqueous phase. At the same time, to date, there have been no reports on the use of hybrid materials of covalent organic frameworks loaded with ionic liquids for the adsorption and separation of rare earth ions. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing an ionic liquid covalent organic framework hybrid material and its application in adsorbing and separating rare earth ions. The present invention uses 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde and 2,5-diaminobenzenesulfonic acid to synthesize a sulfonic acid functionalized covalent organic framework (COF-SO3H) through a Schiff base reaction, and then loads the ionic liquid in the covalent organic framework through ion exchange to prepare an ionic liquid covalent organic framework hybrid material (COF-SO3H-IL). The prepared hybrid material not only solves the dissolution problem of ionic liquid 1-carboxymethyl-3-methylimidazolium chloride in the aqueous phase, but also improves the adsorption performance of the material 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, a carboxyl functional group with a strong affinity for rare earth ions is 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 a more effective rare earth ion capture nanochannel can be constructed in the material, which greatly improves 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 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: The sulfonic acid functionalized covalent organic framework and the ionic liquid 1-carboxymethyl-3-methylimidazolium chloride are treated by an ion exchange method 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.

[0007] Furthermore, 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 liquid; 3) The upper clear liquid and the sulfonic acid functionalized covalent organic framework are stirred at room temperature until the solution becomes neutral.

[0008] 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.

[0009] Furthermore, in step 2), the centrifugation time is 5-15 min, and the centrifugation speed is 5000-10000 rpm.

[0010] Furthermore, 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 obtained reaction solution is degassed through a freeze-thaw cycle, flame-sealed and heated at 100-200° C. for 1-5 days, and the precipitate is collected, washed and dried to obtain a sulfonic acid functionalized covalent organic framework.

[0011] Furthermore, in step 1), the mass ratio of 2,4,6-trihydroxy-1,3,5-benzenetricarboxaldehyde to 2,5-diaminobenzenesulfonic acid is 1:(1-2).

[0012] 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 acetic acid is 6 M.

[0013] 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.

[0014] 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 .

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The ionic liquid covalent organic framework hybrid material prepared by the present invention has high crystallinity and a simple preparation method.

[0016] (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 an aqueous phase.

[0017] (3) The ionic liquid covalent organic framework hybrid material prepared by the present invention introduces a carboxyl functional group having a strong affinity for rare earth ions.

[0018] (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 an efficient rare earth ion capture nanochannel inside the material.

[0019] (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 a high-efficiency adsorbent for low-concentration rare earth tail water. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the preparation process of COF-SO3H.

[0021] Figure 2 These are the experimental test PXRD patterns of Tp, Pa-SO3H and COF-SO3H.

[0022] Figure 3 It is the infrared spectra of Tp, Pa-SO3H and COF-SO3H.

[0023] Figure 4 Schematic diagram of the preparation process of COF-SO3H-IL.

[0024] 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

[0025] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. 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" used herein includes any and all combinations of one or more related listed items.

[0027] Example 1: Preparation and characterization of sulfonated covalent organic frameworks 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, ultrasonicated for 10 minutes, and 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, cooled and filtered, and the obtained white solid product was washed three times with deionized water, N,N-dimethylformamide (DMF), and acetone (Acetone), the solid was collected, and vacuum dried 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° corresponded to the 100, 110, and 001 crystal planes of the material, respectively, indicating that the solvothermal reaction was complete and the synthesized COF-SO3H had good crystallinity.

[0028] Figure 3 It is the infrared spectrum of Tp, Pa-SO3H and COF-SO3H. 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 -1The CN single bond peak formed by the enol-keto tautomerism is located at 1237 cm -1 In COF-SO3H, the -1 The peak at is the S-OH stretching vibration peak of the -SO3H group in the material.

[0029] Example 2: Preparation and characterization of ionic liquid covalent organic framework hybrid materials Figure 4 Figure 1 is a schematic diagram of the preparation process of COF-SO3H-IL. Figure 4 It can be seen that 0.15 mmol of ionic liquid 1-carboxymethyl-3-methylimidazolium chloride was taken and fully dispersed in 20 mL of isopropanol. In addition, 0.3 mmol of potassium hydroxide was taken and fully dispersed in 10 mL of isopropanol. When the above ionic liquid was mixed with the isopropanol solution of potassium hydroxide, it was found that the originally clear solution quickly became turbid, indicating that the ionic liquid and potassium hydroxide underwent an acid-base neutralization reaction and generated the product potassium chloride. The above mixed solution was further stirred at room temperature for 12 h to ensure that the reaction was complete.

[0030] The mixed solution after the above reaction was taken and centrifuged at 8000 rpm for 10 min to remove the insoluble potassium chloride in the mixed solution. After that, the upper clear solution, i.e., the isopropanol solution of the product 1-carboxymethyl-3-methylimidazolium hydroxide salt, was taken by ion exchange method, 0.05 mmol COF-SO3H was added, and it was stirred at room temperature for 12 h. The hydroxyl in the ionic liquid reacted with the proton in COF-SO3H through acid-base neutralization reaction, and the 1-carboxymethyl-3-methylimidazolium cation was exchanged with the proton in COF-SO3H, and the ionic liquid covalent organic framework hybrid material COF-SO3H-IL was prepared. At the same time, it can be observed that the color of the product changes from the brick red of COF-SO3H to the brown of COF-SO3H-IL.

[0031] 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 paper, 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.

[0032] Example 3: Application of ionic liquid covalent organic framework hybrid materials in adsorption and separation of rare earth ions 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 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+ ) was investigated for its adsorption and separation performance. 5 mgCOF-SO3H, COF-SO3H-IL, and COF-SO3H-IL(MC) were added to 10 mL of rare earth mixed solution, respectively, stirred for 12 h, filtered with a 0.22 μm microporous filter membrane, and the content of rare earth ions in the filtrate was measured by inductively coupled plasma emission spectrometry. The distribution coefficients of COF-SO3H, COF-SO3H-IL, and COF-SO3H-IL(MC) for rare earth ions were calculated, respectively, and the affinity of the materials for rare earth ions was studied. 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 better performance than COF-SO3H and COF-SO3H-IL(MC) for 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 due to the fact that COF-SO3H-IL introduces ionic liquids through ion exchange, and 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, 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+ 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 in the solid phase matrix COFs material. The ionic liquid dissolves when it interacts with the aqueous phase, resulting in the inability to transfer the 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.

[0033] The embodiments described above only express several preferred embodiments of the present invention, and the descriptions thereof are relatively specific and detailed, but are not intended to limit the present invention. It should be noted that for those skilled in the art, the present invention may also have various changes and modifications, and any modifications, equivalent substitutions, improvements, etc. made within the concept and principle of the present invention shall be included in the protection scope 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 are treated by an ion exchange method 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 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 and potassium hydroxide is 1:(1.0-2.5); 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 centrifugation 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 obtained reaction solution is degassed through a freeze-thaw cycle, flame-sealed and heated at 100-200° C. for 1-5 days, and 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 concentration of acetic acid 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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