Preparation method and application of MOFs functional group post-modified double functional reinforced cation membrane

Abstract

The application discloses a preparation method and application of a MOFs functional group post-modified double-function reinforced cation membrane, and comprises the following preparation steps: firstly, a UiO-66-NH2 type MOFs material is prepared by using a solvothermal method; secondly, the UiO-66-NH2 type MOFs is post-modified and synthesized into DGA-UiO-66-NH2 by taking an amino group as a center and by being combined with a small-molecule diethylene glycol anhydride (DGA) containing a functional group with specific identification performance for rare earth ions; and then, the prepared functional group modified MOFs is prepared into a polymer coated functional composite membrane in a polymer coating form. The MOFs functional group post-modified double-function reinforced cation membrane prepared by the application shows good selectivity, adsorption and stability for rare earth elements in a simulated acid leaching solution of fly ash, is simple to operate, controllable in cost, and has a good application prospect.

Description

Technical Field

[0001] The invention relates to a preparation method of a MOFs functional group post-modified bifunctional reinforced cationic membrane and application thereof in efficient adsorption and recovery of rare earth elements, belonging to the field of membrane preparation and application. Background Art

[0002] Research has shown that the coexisting ores of coal and coal gangue contain significant amounts of rare earth elements. In some locations, the rare earth element content in coal gangue can reach industrial-grade levels, making it highly valuable for development. After coal combustion, these rare earth elements are incorporated into the fly ash. Therefore, discovering and extracting rare earth elements from fly ash can "turn harm into benefit, turning waste into treasure," while also providing a source of rare earth metal resources. This has important practical implications for the conservation and clean and efficient utilization of my country's mineral resources.

[0003] Metal-organic frameworks (MOFs) are organic-inorganic hybrid materials with intramolecular pores, formed by the self-organization of organic ligands and metal ions or clusters through coordination bonds. They possess advantages such as high porosity, low density, large specific surface area, regular pore structures, tunable pore sizes, diverse topological structures, and ease of modification, making them valuable applications in gas storage, chemical separation, and sensing. The introduction of specific functional groups into MOFs can improve their adsorption properties, hydrophilicity, and ion selectivity. However, powdered MOFs are difficult to recycle in liquid phase separations and suffer from poor recyclability, limiting their industrial application. Membrane separation technology has emerged as a novel separation technique that combines high efficiency, environmental friendliness, and precision. Its ease of operation and manageable cost make it particularly suitable for industrial applications. MOF composite membranes have attracted widespread attention for their superior selectivity and adsorption performance. The ease of modification and tunable pore size of MOFs underpin their efficient and selective separations. By enhancing the interaction between guest molecules and multifunctional metal ions or organic ligands, these membranes can improve separation performance and broaden the applications of MOFs. Polymer-encapsulated membranes (PIMs), a novel liquid membrane, are prepared by dissolving a compound in a volatile organic solvent to form a thin film. As the solvent evaporates, intermolecular forces or interactions between polymer chains contribute to the formation of a highly stable and uniform structure. In this membrane system, the base polymer provides mechanical support, while the plasticizer acts not only as a solvent and carrier but also as a catalyst for ion complex formation. This design lends PIMs to their exceptional performance and promising applications. To further improve the surface affinity of polymer membranes, researchers typically employ methods such as encapsulation with inorganic materials, such as graphene oxide or metal oxide nanoparticles, or by forming homogeneous copolymers. These approaches not only significantly enhance the performance of polymer membranes but also broaden their applications in various fields.

[0004] Compared to traditional separation technologies, PIM offers outstanding stability, shortens metal recovery processes, and reduces carrier usage, making it a promising green and sustainable technology. PIM has been widely used for the selective separation of various metals, including heavy metals, rare earth metals, and platinum group metals. Current PIM membranes primarily utilize traditional liquid extractants as carriers, with few reports on PIM membranes leveraging the easily modifiable and tunable pore size properties of MOFs to enhance ion selectivity. Summary of the Invention

[0005] In order to improve the problem that powdered metal organic framework materials are difficult to recover and have poor recycling performance in liquid phase separation, the technical problem to be solved by the present invention is to provide a MOFs functional group post-modified bifunctional reinforced cationic coating membrane that is easy to produce and prepare and has specific selectivity and recyclability for rare earth ions.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] The present invention first discloses a preparation method of a MOFs functional group post-modified dual-functional enhanced cationic membrane. The method uses UiO-66-NH2 type MOFs as a matrix material and amino groups as the center. The UiO-66-NH2 type MOFs are post-modified by small molecules containing functional groups with specific recognition characteristics for rare earth ions to introduce abundant amide carboxyl groups. Subsequently, a substrate and a plasticizer are added, and the MOFs functional group post-modified dual-functional enhanced cationic membrane is prepared by polymer coating and blending.

[0008] Preferably, the preparation method of the MOFs functional group post-modified bifunctional enhanced cationic membrane comprises the following steps:

[0009] 1) Zirconium tetrachloride and 2-aminoterephthalic acid were added to N,N-dimethylformamide (DMF). An appropriate amount of concentrated hydrochloric acid was then added. The mixture was stirred at room temperature to thoroughly mix, and then transferred to a polytetrafluoroethylene-lined reactor for incubation. After the reaction was complete, the temperature was naturally lowered. The resulting reaction solution was centrifuged and filtered, washed sequentially with DMF and ethanol, and dried in a vacuum oven at 60-80°C to obtain a pale yellow powder of UiO-66-NH2 MOFs.

[0010] 2) mixing the UiO-66-NH2 type MOFs obtained in step 1) with a small molecule containing a functional group having specific recognition characteristics for rare earth ions, reacting the mixture at room temperature under nitrogen protection for 24 h to 36 h, filtering the resulting reaction solution, washing with ethanol, and drying under vacuum at 60-80°C to obtain functional group-modified MOFs;

[0011] 3) The functional group post-modified MOFs powder obtained in step 2) is mixed with a substrate and a plasticizer, stirred at 20-60 DEG C for 1-4 h, and then stirred at room temperature for 1-2 h to remove bubbles, to obtain a casting solution; the casting solution is poured on a glass plate, and a casting machine is used to scrape the solution flat, to obtain a polymer-coated MOFs composite film with a thickness of 20-100 microns; the film is naturally air-dried in a fume hood until the solvent is completely volatilized, the film is taken out, and washed with deionized water, to obtain a light yellow MOFs functional group post-modified bifunctional cation-strengthened film.

[0012] Preferably, in step 1), the molar ratio of zirconium tetrachloride to 2-amino terephthalic acid is 1:(1-1.2).

[0013] Preferably, in step 1), the reaction temperature of the heat preservation reaction is 120-200 DEG C, and the reaction time is 24-48 h.

[0014] Preferably, in step 2), the small molecule is diethanol anhydride (DGA), and the mass ratio of the UiO-66-NH2 type MOFs to diethanol anhydride is 1:0.2-1, and the functional group post-modified MOFs obtained is DGA-UiO-66-NH2 type MOFs particles.

[0015] Preferably, in step 3), the substrate is any one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and polyvinyl chloride (PVC); and the plasticizer is any one of 2-nitrophenyl octyl ether (2-NPOE), 2-nitrophenyl pentyl ether (2-NPPE), and dioctyl adipate (DOA).

[0016] Preferably, in step 3), the functional group post-modified MOFs powder, the substrate, and the plasticizer are composed of the functional group post-modified MOFs powder 10-40%, the PVDF 20-40%, and the plasticizer 20-50% by mass percentage.

[0017] The application further discloses an application of the MOFs functional group post-modified bifunctional cation-strengthened film prepared according to the preparation method in selective adsorption of rare earth ions.

[0018] The application has the following beneficial effects:

[0019] (1) The preparation method of the ion film is simple and easy to operate, the raw materials are cheap, mass production is possible, and the method is suitable for industrial application,

[0020] (2) The ion membrane prepared by the application has specific selectivity to rare earth ions and good recycling performance, large water flux, good stability, and excellent ion precision separation characteristics. In addition, the membrane material obtained by the application can not only play the chelation of functional groups to rare earth ions and the pore size screening of MOFs to ions, but also fully play the advantages of high efficiency and environmental protection of membrane separation. The material can be used for the separation process of rare earth ions and has unique advantages in actual application. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A preparation schematic diagram of the MOFs functional group post-modified bifunctional reinforced cationic membrane of the application;

[0022] Figure 2 XRD diagrams of the UiO-66-NH2, DGA-UiO-66-NH2 and DGA-UiO-66-NH2@PVDF cationic membranes prepared in Example 1 of the application;

[0023] Figure 3 Infrared spectra of the UiO-66-NH2, DGA-UiO-66-NH2 and DGA-UiO-66-NH2@PVDF cationic membranes prepared in Example 1 of the application;

[0024] Figure 4 Chemical stability analysis results of the DGA-UiO-66-NH2 prepared in Example 1 of the application in aqueous solutions at different pH values;

[0025] Figure 5 Selectivity analysis diagram of the DGA-UiO-66-NH2@PVDF cationic membrane prepared in Example 1 of the application to different metal ions;

[0026] Figure 6 Comparison results of the adsorption amount of the DGA-UiO-66-NH2@PVDF cationic membrane prepared in Example 1 of the application to different rare earth elements in different acidity solutions;

[0027] Figure 7 Comparison results of the adsorption amount of the DGA-UiO-66-NH2@PVDF cationic membrane prepared in Example 1 of the application to different rare earth elements under different contact times;

[0028] Figure 8 Adsorption amount and adsorption isotherm analysis of the DGA-UiO-66-NH2@PVDF cationic membrane prepared in Example 1 of the application to rare earth elements with different initial dissolved concentrations. DETAILED DESCRIPTION

[0029] In order to more fully understand the present invention, this embodiment describes the present invention in more detail through the following non-limiting examples or comparative examples, and provides detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following examples.

[0030] Example 1: Preparation of a MOFs functional group post-modified bifunctional enhanced cationic membrane

[0031] (1) Preparation of UiO-66-NH2 MOFs: Zirconium tetrachloride (1.16 g, 5.0 mmol) and 2-aminoterephthalic acid (0.9 g, 5.0 mmol) were placed in a beaker containing 30 mL of N,N-dimethylformamide (DMF) solution. 100 μL of concentrated hydrochloric acid was added and stirred at room temperature to mix thoroughly. The mixture was then transferred to a polytetrafluoroethylene-lined reactor. The reaction was carried out at 120°C for 24 h. After the reaction was completed, the temperature was naturally lowered. The resulting reaction solution was centrifuged and filtered. The synthesized product was washed with DMF and ethanol solutions in sequence and then dried in a vacuum drying oven at 70°C for 6 h to obtain a light yellow UiO-66-NH2 MOFs powder.

[0032] (2) Preparation of DGA-modified UiO-66-NH2 type MOFs (DGA-UiO-66-NH2 type MOFs): 4.0 g of the MOFs obtained in step (1) was mixed with 1.2 g of diglycolic anhydride, and 20 mL of dichloromethane was added. The mixture was reacted at room temperature for 24 h under N2 protection. The resulting reaction solution was filtered, and the solid was washed three times with ethanol and then washed with distilled water until neutral. The solid was vacuum dried at 60°C for 6 h to obtain DGA-UiO-66-NH2 type MOFs.

[0033] (3) Preparation of composite membrane: 30% DGA-UiO-66-NH2 type MOFs powder, 30% PVDF, and 40% 2-NPOE were added to a round-bottom flask. A magnet was added and the mixture was stirred at 50°C for 2 h. Then, the mixture was stirred at room temperature for 1 h to remove bubbles. The casting solution was poured onto a glass plate and smoothed with a 50 μm film caster. The mixture was naturally air-dried in a fume hood for 12 h to completely evaporate the solvent. The membrane was removed and rinsed with deionized water to obtain a light yellow DGA-UiO-66-NH2@PVDF dual-functional reinforced cationic membrane.

[0034] Example 2: Characterization of a MOFs functional group post-modified bifunctional enhanced cationic membrane

[0035] The XRD analysis of the DGA-UiO-66-NH2@PVDF cationic membrane prepared in Example 1 is as follows: Figure 2As shown in the figure, UiO-66-NH2, DGA-UiO-66-NH2 and DGA-UiO-66-NH2@PVDF ion membranes all have two good characteristic peaks between 5° and 10°, UiO-66-NH2 and DGA-UiO-66-NH2 have a good characteristic peak between 25° and 27°, and the characteristic peak of DGA-UiO-66-NH2@PVDF ion membrane is very weak, which may be due to the interference of PVDF material, indicating that loading DGA-UiO-66-NH2 onto PVDF does not change the crystal structure of the loaded material.

[0036] The infrared spectrum of the DGA-UiO-66-NH2@PVDF dual-functional reinforced cationic membrane prepared in Example 1 is as follows: Figure 3 As shown. In the infrared spectrum of DGA-UiO-66-NH2, 1250 cm -1 The vibration absorption peak of carboxyl group appeared at 1100 cm -1 to 1200 cm -1 A vibration absorption peak appeared at 1570 cm-1, which was caused by the ether bond generated by the ring opening of DGA modification on UiO-66-NH2. -1 There is a strong vibration absorption peak at 750cm, indicating the presence of C=O carbonyl, which means that DGA is successfully modified on UiO-66-NH2. The infrared absorption peak generated by the ion membrane DGA-UiO-66-NH2@PVDF is known to be at 750cm -1 The absorption peak of benzene ring appears at 1100 cm -1 to 1200 cm -1 The vibration absorption peak of the ether bond in DGA-UiO-66-NH2 appeared, indicating that the material DGA-UiO-66-NH2 was successfully loaded on PVDF.

[0037] The chemical stability analysis of DGA-UiO-66-NH2 prepared in Example 1 is as follows Figure 4As shown in the figure, 30 mg of DGA-UiO-66-NH2 was weighed and placed in aqueous solutions with pH values ​​of 2, 4, 6, 8, 10, and 12, soaked for 2 hours, and then dried. XRD tests were then performed on the same materials as untreated UiO-66-NH2 and DGA-UiO-66-NH2. A comparison of UiO-66-NH2 and DGA-UiO-66-NH2 reveals two distinct characteristic peaks between 5° and 10°, and one distinct characteristic peak between 25° and 27°, indicating that the reaction between DGA and UiO-66-NH2 did not change the crystal structure of the original material. The spectra obtained after DGA-UiO-66-NH2 was soaked in aqueous solutions with different pH values ​​show that the characteristic peaks did not change, indicating that DGA-UiO-66-NH2 has good chemical stability.

[0038] Example 3: Application of a MOFs functional group post-modified dual-functional enhanced cationic membrane

[0039] Selectivity analysis of the DGA-UiO-66-NH2@PVDF ion membrane prepared in Example 1 for different metal ions: 30 mg of DGA-UiO-66-NH2 material was added to 10 mL of DMF solution containing different metal ions (concentration of 0.01 mol / L), and fluorescence detection was performed at an excitation wavelength of 340 nm to 560 nm after shaking for 30 min. Figure 5 As shown in the figure, Ce element has the most obvious fluorescence quenching effect on DGA-UiO-66-NH2, which also shows that DGA-UiO-66-NH2 has the best selectivity for Ce element among rare earth elements, followed by La and Nd elements.

[0040] The adsorption capacity of different rare earth elements by the DGA-UiO-66-NH2@PVDF ion membrane prepared in Example 1 in solutions with different acidity: The concentrations of La, Ce, and Nd ions in the prepared fly ash acid leaching simulation solution were 25 mg / L, 43 mg / L, and 20 mg / L, respectively. 20 mL of the standby solution with different pH values ​​was taken, and 0.069 g of a DGA-UiO-66-NH2@PVDF ion membrane with a loading of 30% was added to each of them. The mixture was shaken in a water bath at 25°C for 2 h, and the membrane material was filtered to obtain the supernatant. The ion concentrations before and after the reaction were determined by ICP. Q e is the adsorption amount, and the calculation formula is:

[0041]

[0042] Where: C0 represents the mass concentration before adsorption (mg / g); C erepresents the mass concentration after adsorption (mg / g); V represents the volume of the adsorption liquid (mL); M represents the mass of the adsorption material (g). Figure 6 As shown in the figure, with the increase of acidity, the adsorption capacity of La, Ce, and Nd by the composite membrane gradually increased, reaching the maximum at pH 4, which were 130.43 μg / g, 165.22 μg / g, and 86.96 μg / g, respectively.

[0043] The adsorption capacity of different rare earth elements by the DGA-UiO-66-NH2@PVDF ion membrane prepared in Example 1 at different contact times was as follows: 0.1658 g of the composite membrane was dissolved in 40 mL of different ion solutions (the concentrations of La, Ce, and Nd ions were 25 mg / L, 43 mg / L, and 20 mg / L, respectively). At the above optimal pH, the mixture was kept constant temperature in a 25°C water bath oscillator. 1 mL of the reaction solution was drawn at 10 min, 20 min, 30 min, 45 min, 60 min, 90 min, 120 min, 150 min, 180 min, and 240 min, respectively, and the volume was fixed to a 10 mL volumetric flask for measurement. The results are shown in Figure 2. Figure 7 As shown in the figure, the adsorption amount of La, Ce and Nd continues to increase with time. This is because there are many binding sites for rare earth elements on the composite membrane, and a large amount of rare earth elements are bound and adsorbed on the composite membrane with time. At 150 min, the adsorption amount of La, Ce and Nd by DGA-UiO-66-NH2@PVDF ion membrane reaches the maximum, which are 149.58 μg / g, 180.90 μg / g and 98.91 μg / g respectively.

[0044] The adsorption capacity and adsorption isotherm analysis of the DGA-UiO-66-NH2@PVDF ion membrane prepared in Example 1 for rare earth elements with different initial dissolved concentrations: about 0.071 g of membrane material was added to 20 mL of solutions with La concentrations of 5-200 mg / L, Ce concentrations of 8.6-344 mg / L, and Nd concentrations of 4-160 mg / L, respectively. The membrane was shaken in a constant temperature water bath at 25°C for 2 h, and the ion concentrations before and after the reaction were measured by ICP. The results are as follows: Figure 8As shown in the figure, the adsorption capacity gradually increases with increasing concentration. After reaching a certain concentration, the adsorption capacity no longer increases, reaching adsorption saturation. The optimal initial concentrations of La, Ce, and Nd are 150 mg / L, 258 mg / L, and 120 mg / L, respectively, at which the adsorption capacities are 253.52 μg / g, 425.35 μg / g, and 233.80 μg / g, respectively. The adsorption experimental data of La, Ce, and Nd on the DGA-UiO-66-NH2@PVDF ion membrane are more consistent with the Langmuir model, indicating that the adsorption process of the adsorbent for rare earth elements is monolayer adsorption.

[0045] The above description is merely an exemplary embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A method for preparing a MOFs functional group post-modified bifunctional enhanced cationic membrane, characterized by: Using UiO-66-NH2 type MOFs as the matrix material, UiO-66-NH2 type MOFs were post-modified by small molecule diglycolic anhydride containing functional groups with specific recognition characteristics for rare earth ions, and then a substrate and plasticizer were added to prepare the target cationic membrane by polymer coating and blending; among them, the mass ratio of UiO-66-NH2 type MOFs to diglycolic anhydride was 1:0.2-1.

2. The preparation method according to claim 1, characterized in that The following steps are involved: 1) Zirconium tetrachloride and 2-aminoterephthalic acid were added to N,N-dimethylformamide, and concentrated hydrochloric acid was added. The mixture was stirred at room temperature to fully mix, and then transferred to a polytetrafluoroethylene-lined reactor for heat reaction. After the reaction was completed, the temperature was naturally lowered, and the resulting reaction solution was centrifuged, washed, and vacuum-dried to obtain UiO-66-NH2 type MOFs. 2) mixing the UiO-66-NH2 type MOFs obtained in step 1) with a small molecule containing a functional group having specific recognition characteristics for rare earth ions, reacting at room temperature under nitrogen protection, and filtering, washing, and vacuum drying the resulting reaction solution to obtain functional group-modified MOFs; 3) The functional group-post-modified MOFs powder obtained in step 2) is mixed with a substrate and a plasticizer, stirred at 20-60° C. for 1-4 hours, and then stirred at room temperature for 1-2 hours to remove bubbles, thereby obtaining a casting solution; the casting solution is poured onto a glass plate and flattened with a film caster to obtain a polymer-coated MOFs composite membrane, which is naturally air-dried in a fume hood until the solvent is completely evaporated, and the membrane is removed and rinsed with deionized water to obtain a MOFs functional group-post-modified bifunctional reinforced cationic membrane.

3. The preparation method according to claim 2, characterized in that In step 1), the molar ratio of zirconium tetrachloride to 2-aminoterephthalic acid is 1:1-1.

2.

4. The preparation method according to claim 2, wherein In step 1), the reaction temperature of the insulation reaction is 120-200° C., and the reaction time is 24-48 h.

5. The preparation method according to claim 2, wherein: In step 3), the matrix is ​​any one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and polyvinyl chloride; and the plasticizer is any one of 2-nitrophenyl octyl ether, 2-nitrophenyl pentyl ether, and dioctyl adipate.

6. The preparation method according to claim 2, wherein: In step 3), the composition of the functional group post-modified MOFs powder, the substrate, and the plasticizer in terms of mass percentage is: 10-40% of the functional group post-modified MOFs powder, 20-40% of the substrate, and 20-50% of the plasticizer.

7. The preparation method according to claim 2, characterized in that The thickness of the prepared polymer-coated MOFs composite film is 10-100 μm.

8. A MOFs functional group post-modified bifunctional enhanced cationic membrane prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the MOFs functional group post-modified bifunctional enhanced cationic membrane according to claim 8 in the selective adsorption of rare earth ions.

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