Double-layer metal organic framework composite membrane for selective ion separation and application of double-layer metal organic framework composite membrane

Abstract

The invention discloses a double-layer metal organic framework composite membrane for ion selective separation and application thereof.The composite membrane is prepared by the steps that anodic aluminum oxide (AAO) serves as a substrate, firstly, a layer of ZIF-108 grows on the surface of the AAO through an anti-diffusion method, a ZIF-108-coated AAO intermediate membrane is formed, then a layer of ZIF-8 grows on the surface of the ZIF-108-coated AAO intermediate membrane, and finally the double-layer metal organic framework composite membrane is obtained. The membrane is marked as the ZIF-8 / ZIF-108 coated AAO composite membrane. The obtained composite membrane has high monovalent and multivalent ion selectivity, can realize high-selectivity separation of monovalent and multivalent cations in a short time, can be applied to the fields of resource utilization and water treatment such as salt lake lithium extraction, seawater desalination and the like, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a bilayer metal-organic framework composite membrane for ion selective separation and its application. Background Technology

[0002] Metal-organic framework (MOF) films are porous crystalline thin films constructed by coordination bonds between metal ions / clusters and organic ligands, possessing ultra-high specific surface areas (1000-7000 m²). 2 It features atomically tunable pores (0.3-3 nm) and functional designability. It has wide applications in gas separation (such as efficient CO2 capture using ZIF-8 membranes), water treatment (degradation of organic pollutants), and energy storage (improving the cycle life of lithium-sulfur batteries). It boasts excellent sieving performance and easily tunable functionality, but also suffers from insufficient stability under high temperature and humidity conditions and high precursor costs, which to some extent hinders its industrialization.

[0003] Ion selective separation is in high demand in fields such as lithium extraction from salt lakes, wastewater resource utilization, and drinking water purification. Traditional membrane separation technologies (such as nanofiltration membranes) rely on the pore size sieving and charge effect of polymer materials, but due to the disordered pores and single selectivity, it is difficult to balance ion transport flux and precise separation effect. Metal-organic framework (MOF) materials have become ideal candidate materials for ion separation membranes due to their tunable pore size and functionalized pore structure. However, single MOF membranes have two major bottlenecks: (1) the narrow pores of highly selective MOFs (such as ZIF-8, with a theoretical pore size of about 3.4 Å) result in high ion diffusion resistance and low flux; (2) the wide pores of highly permeable MOFs (such as ZIF-108, with a theoretical pore size of about 3.6 Å) make it difficult to distinguish the size differences of different ions and achieve precise sieving.

[0004] In existing research, the article "Designing Angstrom-Scale Asymmetric MOF-on-MOFCavities for High Monovalent Ion Selectivity" [1] A composite membrane composed of a bilayer metal-organic framework (MOF-on-MOF) with a permeable cavity structure of 6 to 3.4 Å was prepared. Ion current measurements showed that its ion current rectification ratio exceeded 100, and it was effective for K+. + / Li + and Na + / Li + The selectivity was as high as 84 and 80 (Li) respectively. + The flux was 1.14 mol m -2 h -1). Article "Bioinspired Angstrom-Scale Heterogeneous MOF-on-MOF Membrane for Osmotic Energy Harvesting" [2] A bilayer metal-organic framework (MOF-on-MOF) membrane was prepared, in which the ZIF-8 layer enhances ion selectivity through the size repulsion effect of Elstrand-level pores, while the intercalated PSS-UiO-66-NH2 membrane ensures cation permeability. The two work synergistically to achieve simultaneous improvement in ion transport efficiency and selectivity.

[0005] References: 1. M. Abdollahzadeh, M. Chai, E. Hosseini, M. Zakertabrizi, M.Mohammad, H. Ahmadi, J. Hou, S. Lim, A. Habibnejad Korayem, V. Chen, M.Asadnia, A. Razmjou, Designing angstrom-scale asymmetric MOF-on-MOF cavities for high monovalent ion selectivity, Adv. Mater. 34 (2022) 2107878. 2. Rockson Kwesi Tonnah, Milton Chai, Mojtaba Abdollahzadeh etal. Bioinspired Angstrom-Scale Heterogeneous MOF-on-MOF Membrane for OsmoticEnergy Harvesting. ACS Nano 2023 17 (13), 12445-12457. Summary of the Invention

[0006] Based on the aforementioned prior art, this invention provides a bilayer metal-organic framework composite membrane for ion selective separation and its application. The composite membrane is a ZIF-8 / ZIF-108@AAO bilayer composite membrane with tight interfacial bonding and controllable pore size gradient. It aims to solve the trade-off between flux and selectivity in monovalent and multivalent ion separation through the synergistic effect of "bottom layer support - top layer sieving", so that the composite membrane has both high flux and high monovalent and multivalent ion selectivity.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a bilayer metal-organic framework composite membrane for ion selective separation. The composite membrane is based on anodic aluminum oxide (AAO). First, a layer of ZIF-108 is grown on the surface of AAO by reverse diffusion to form a ZIF-108@AAO intermediate membrane. Then, a layer of ZIF-8 is grown on the surface of the ZIF-108@AAO intermediate membrane to finally obtain a bilayer metal-organic framework composite membrane, denoted as ZIF-8 / ZIF-108@AAO composite membrane.

[0008] The preparation method of the ZIF-8 / ZIF-108@AAO composite membrane of the present invention includes the following steps: Step 1: Pretreatment of AAO membrane The AAO membrane was placed in ethanol and deionized water in sequence, and ultrasonically cleaned for 5-15 minutes each time, and then dried for later use. Step 2: Preparation of ZIF-108@AAO intermediate membrane Anhydrous zinc acetate was dissolved in DMF to prepare solution A; 2-nitroimidazole was dissolved in DMF to prepare solution B. The pretreated AAO membrane was placed in a diffusion device to separate solution A from solution B, and then placed in an oven at 50-60°C for 6-10 hours. After the reaction was completed, the membrane was washed with DMF and then dried to obtain ZIF-108@AAO intermediate membrane. Step 3: Preparation of ZIF-8 / ZIF-108@AAO composite membrane Solution C was prepared by dissolving zinc nitrate hexahydrate in methanol solution; solution D was prepared by dissolving 2-methylimidazole in methanol solution. The ZIF-108@AAO intermediate membrane was first immersed in solution C and reacted at room temperature for 1-2 hours. After being removed and air-dried, it was transferred to solution D and reacted at room temperature for 3-5 hours. After being removed, rinsed with methanol, and dried, the ZIF-8 / ZIF-108@AAO composite membrane was obtained.

[0009] As a further preferred embodiment of the present invention, in step 2, the molar ratio of 2-nitroimidazole to anhydrous zinc acetate is 2:1.

[0010] As a further preferred embodiment of the present invention, in step 3, the molar ratio of 2-methylimidazole to zinc nitrate hexahydrate is 8:1.

[0011] As a further preferred embodiment of the present invention, in steps 1, 2 and 3, the drying temperature is 60~80℃.

[0012] The ZIF-8 / ZIF-108@AAO composite membrane provided by this invention can be used as a selective separation membrane for monovalent and multivalent cations, such as in brine separation and seawater desalination.

[0013] Compared with existing technologies, the beneficial effects of this invention are reflected in: 1. This invention uses a stepwise growth process to prepare ZIF-8 / ZIF-108@AAO composite membranes. The operation process is simple, the reaction conditions are easy to control, and the reproducibility is strong, which is conducive to large-scale preparation.

[0014] 2. The ZIF-8 / ZIF-108@AAO composite membrane obtained in this invention possesses multi-level pores. Due to the structural differences between ZIF-108 and ZIF-8, it exhibits high selectivity for monovalent and polyvalent ions, enabling highly selective separation of monovalent and polyvalent ions in a short time. Compared to single MOF membranes (such as ZIF-8 or ZIF-108 membranes alone), it effectively solves the pain point of "difficulty in balancing flux and selectivity" in ion separation, significantly improving separation efficiency. Through highly efficient ion-selective separation, it significantly improves the separation efficiency of target ions (such as Li). + Na + With its high recovery efficiency (etc.), it has a wide range of applications, such as lithium extraction from salt lakes and seawater desalination, and has good prospects for industrial application. Attached Figure Description

[0015] Figure 1 This is an XRD pattern of the ZIF-8 / ZIF-108@AAO composite membrane prepared in Example 1 of the present invention.

[0016] Figure 2 The ZIF-8 / ZIF-108@AAO composite membrane prepared in Example 1 ( Figure 2 (a) in the example and the ZIF-108@AAO membrane prepared in Comparative Example 1 ( Figure 2 SEM image of (b) in the image.

[0017] Figure 3 The flux of ZIF-8 / ZIF-108@AAO composite membranes prepared in Examples 1 and 2 and the ZIF-108 membrane prepared in Comparative Example 1 for different ions ( Figure 3 (a), (c), (e) in the text) and the separation selectivity of each ion pair ( Figure 3 In the examples (b), (d), and (f), (a) and (b) correspond to Example 1, (c) and (d) correspond to Example 2, and (e) and (f) correspond to Comparative Example 1. Detailed Implementation

[0018] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0019] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0020] Example 1 In this embodiment, the ZIF-8 / ZIF-108@AAO composite membrane for ion selective separation was prepared according to the following steps: Step 1: Pretreatment of AAO membrane The AAO membrane was placed in ethanol and deionized water in sequence, and ultrasonically cleaned for 10 minutes each time. Then it was dried in an oven at 60°C for later use.

[0021] Step 2: Preparation of ZIF-108@AAO intermediate membrane Weigh 0.183 g of anhydrous zinc acetate into a beaker, add 40 mL of DMF, and sonicate at room temperature for 30 min to prepare solution A. Take 0.226 g of 2-nitroimidazole into a beaker, add 40 mL of DMF, and stir at room temperature for 30 min to prepare solution B. Pour solutions A and B separately into a glass container containing a pretreated AAO membrane, separating solutions A and B. Then, place the container in a 50 °C oven for 10 h. After the reaction, wash the membrane three times with DMF and then dry it in a 60 °C oven to obtain the ZIF-108@AAO intermediate membrane.

[0022] Step 3: Preparation of ZIF-8 / ZIF-108@AAO composite membrane 2.230 g of zinc nitrate hexahydrate was weighed into a beaker, 40 mL of methanol was added, and the mixture was sonicated for 30 min at room temperature to obtain solution C. 9.852 g of 2-methylimidazole was weighed into a beaker, 40 mL of methanol was added, and the mixture was stirred for 30 min at room temperature to obtain solution D. The ZIF-108@AAO intermediate membrane was first immersed in solution C and reacted at room temperature for 2 h to enrich its surface with Zn. 2+ After being removed and air-dried, the mixture was transferred to solution D and reacted at room temperature for 4 hours. After the reaction was completed, the mixture was removed, rinsed three times with methanol, and then dried at 60°C to obtain the ZIF-8 / ZIF-108@AAO composite membrane.

[0023] Example 2 In this embodiment, the ZIF-8 / ZIF-108@AAO composite membrane was prepared using the same method as in Example 1, except that the reaction time in step 2 was changed from 10 hours to 6 hours.

[0024] Comparative Example 1 This comparative example uses the ZIF-108@AAO intermediate membrane prepared in step 2 of Example 1 as a comparison.

[0025] Figure 1 The image shows the XRD pattern of the ZIF-8 / ZIF-108@AAO composite film prepared in Example 1. This film is a MOF-on-MOF bilayer composite structure prepared with AAO as the substrate. In the image, the characteristic peaks appearing at 2θ≈7.4°, 10.4°, 12.6°, and 14.8° correspond to the (111), (220), (311), and (222) crystal planes, respectively. Compared with the standard XRD of ZIF-8, the interplanar spacing of the sample is increased, and the peak position may shift to the left by about 0.1°, but the peak shape and relative intensity are basically stable. Since the characteristic peaks of ZIF-108 and ZIF-8 are extremely similar, and due to the coverage of the characteristic peaks of ZIF-8, the characteristic peaks of ZIF-108 may overlap with those of ZIF-8.

[0026] Figure 2 The ZIF-8 / ZIF-108@AAO composite membrane prepared in Example 1 ( Figure 2 (a) in the example and the ZIF-108@AAO membrane prepared in Comparative Example 1 ( Figure 2 The SEM image in (b) shows that the prepared membrane surface is relatively dense and smooth, and the size of ZIF-108 nanoparticles is larger than that of ZIF-8 nanoparticles, which provides a site for the growth of ZIF-8 nanoparticles on the ZIF-108@AAO membrane surface.

[0027] An electrodialysis apparatus containing two electrode chambers, one desalination chamber, and one concentration chamber was used to test the ion separation performance of the membranes obtained in the above embodiments and comparative examples. The specific procedure is as follows: Device assembly: Assemble a device with a diameter of 2cm (effective area 3.14 cm²). 2 The test membrane (ZIF-8 / ZIF-108@AAO membrane or ZIF-8@AAO membrane) is placed in the center of the electrodialysis device to separate the concentration chamber and the desalination chamber; anion exchange membranes are used to separate the electrode chamber from the desalination chamber and the electrode chamber from the concentration chamber.

[0028] Test conditions: Current density is 2 mA·cm -2 The electrodialysis test lasted for 1 hour.

[0029] Solution preparation: K + / Mg 2+ Na+ / Mg 2+ and Li + / Mg 2+ Electro-driven cation-selective permeation performance of three separation systems. For K + / Mg 2+ In the separation system, 100 mL of 0.1 mol L⁻¹ solution was added to the desalination chamber. -1 KCl and 0.1 mol L -1 A mixed solution of MgCl2 was concentrated by adding 100 mL of deionized water. For Na... + / Mg 2+ In the separation system, 100 mL of 0.1 mol L⁻¹ solution was added to the desalination chamber. -1 NaCl and 0.1 mol L -1 A mixed solution of MgCl2 was concentrated with 100 mL of deionized water. For Li... + / Mg 2+ In the separation system, 100 mL of 0.1 mol L⁻¹ solution was added to the desalination chamber. -1 LiCl and 0.1 mol L -1 A mixed solution of MgCl2 was added, while 100 mL of deionized water was added to the concentration chamber. In each of the three separation systems, 100 mL of 0.3 mol / L MgCl2 solution was added to the electrode chamber. -1 Na2SO4 solution.

[0030] Detection and Analysis: After 1 hour of electrodialysis, samples were taken from the concentration chamber and the cations (K+) in the samples were determined using an intra-inductively coupled plasma optical emission spectrometer (ICP-AES). + Na + Li + Mg 2+ The concentration of ions was used to evaluate the electro-driven cation selective permeation performance of the membrane.

[0031] The flux of cations through the membrane is calculated by the change in cation concentration in the concentration chamber before and after the test. The calculation formula is as follows: (1) in, J N n+ It is a cation N Flux through the membrane (in mol h) -1 m -2 ), C 0 and C t They are cations N The initial concentration and the concentration at the end of the electrodialysis test (in mol L). -1), V It is the volume of the solution in the concentration chamber. A It is the effective area of ​​the membrane. t The test duration is 1 hour.

[0032] Based on this, the cation permeation selectivity P(M) of the membrane is calculated using formula (2). + / D 2+ ): (2) in, and This refers to the flux of monovalent and divalent cations permeating the membrane after testing (in mol / h). -1 m -2 ), and These are the monovalent cations (K+) in the desalination chamber during the experiment. + Na + Or Li + ) and divalent cations (Mg 2+ The average concentration (in mol L) -1 ).

[0033] Experimental results are as follows Figure 3 As shown. A comparison reveals: ZIF-8 / ZIF-108@AAO composite membrane for Na + / Mg 2+ The separation selectivity of ions is significantly higher than that of other ion pairs (K). + / Mg 2+ Li + / Mg 2+ This is the advantageous direction for the membrane in the separation of monovalent and multivalent ions.

[0034] When the reaction time is controlled at 10 hours: the bilayer membrane can stably maintain a high Na content. + / Mg 2+ Selectivity; compared with the ZIF-108@AAO single membrane of Comparative Example 1, although it makes Na + / Mg 2+ K + / Mg 2+ With Li + / Mg 2+ The ion flux of the system was reduced, but it effectively compensated for the core defect of low selectivity of a single MOF membrane, and achieved synergistic optimization of "flux-selectivity".

[0035] When the reaction time is shortened to 6 hours: K + Na + Li + Mg 2+The ion flux was significantly increased compared to the 10h group, but the corresponding Na... + / Mg 2+ Plasma pair selectivity decreased to some extent, showing a trend of "increased flux - decreased selectivity".

[0036] Considering both ion selectivity and flux, the ZIF-8 / ZIF-108@AAO membrane exhibited the best overall separation performance when the growth reaction time of ZIF-108 on the AAO substrate was controlled at 10 h. This membrane can not only be used for the efficient extraction of sodium ions from brine systems, but also for the biomimetic Na+ extraction. + The construction of ion channels provides a feasible approach.

[0037] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A bilayer metal-organic framework composite membrane for ion selective separation, characterized in that: The composite film is based on anodic aluminum oxide (AAO). First, a layer of ZIF-108 is grown on the surface of AAO using a reverse diffusion method to form a ZIF-108@AAO intermediate film. Then, a layer of ZIF-8 is grown on the surface of the ZIF-108@AAO intermediate film to finally obtain a double-layer metal-organic framework composite film, denoted as ZIF-8 / ZIF-108@AAO composite film.

2. A method for preparing the bilayer metal-organic framework composite membrane for ion selective separation as described in claim 1, characterized in that, Includes the following steps: Step 1: Pretreatment of AAO membrane The AAO membrane was placed in ethanol and deionized water in sequence, and ultrasonically cleaned for 5-15 minutes each time, and then dried for later use. Step 2: Preparation of ZIF-108@AAO intermediate membrane Anhydrous zinc acetate was dissolved in DMF to prepare solution A; 2-nitroimidazole was dissolved in DMF to prepare solution B. The pretreated AAO membrane was placed in a diffusion device to separate solution A from solution B, and then placed in an oven at 50-60°C for 6-10 hours. After the reaction was completed, the membrane was washed with DMF and then dried to obtain ZIF-108@AAO intermediate membrane. Step 3: Preparation of ZIF-8 / ZIF-108@AAO composite membrane Zinc nitrate hexahydrate was dissolved in methanol to prepare solution C; 2-methylimidazole was dissolved in methanol to prepare solution D. The ZIF-108@AAO intermediate membrane was first immersed in solution C and reacted at room temperature for 1-2 hours. After being removed and air-dried, it was transferred to solution D and reacted at room temperature for 3-5 hours. After being removed, rinsed with methanol, and dried, the ZIF-8 / ZIF-108@AAO composite membrane was obtained.

3. The preparation method according to claim 2, characterized in that, In step 2, the molar ratio of 2-nitroimidazole to anhydrous zinc acetate is 2:

1.

4. The preparation method according to claim 2, characterized in that, In step 3, the molar ratio of 2-methylimidazole to zinc nitrate hexahydrate is 8:

1.

5. The preparation method according to claim 2, characterized in that, In steps 1, 2, and 3, the drying temperature is 60~80℃.

6. The application of the ZIF-8 / ZIF-108@AAO composite membrane as a selective separation membrane for monovalent and multivalent cations as described in claim 1.

Images