An ultrahigh valence / multivalent cation-selective two-dimensional layered membrane and a preparation method and application thereof

Abstract

The application discloses a two-dimensional layered membrane with super-high monovalent / multivalent cation selectivity and a preparation method and application thereof, and the two-dimensional layered membrane is a membrane formed by stacking modified graphene oxide, wherein the inner wall of a channel in the membrane is grafted with amino groups (-NH2); and the surface of the membrane is modified with carboxyl groups (-COOH) and is coordinated with high-valence cations. The membrane has super-high selectivity to monovalent / multivalent cations.

Description

Technical Field

[0001] This invention belongs to the field of ion transport technology, specifically relating to a method for preparing a two-dimensional layered membrane for selective separation and rapid transport of ultra-high monovalent / multivalent cations. Background Technology

[0002] The development of artificial membranes for rapid and selective ion transport is crucial for modern separation technologies and has attracted widespread attention in fields such as lithium extraction from salt lakes, chlor-alkali industry, and heavy metal ion removal. Two-dimensional nanomaterials possess advantages such as single-atom-layer thickness, large aspect ratio, good mechanical properties, and ease of film formation, making them ideal separation membrane materials.

[0003] Two-dimensional layered films are assembled by stacking two-dimensional nanosheets layer by layer through vacuum filtration, spin coating, drop coating and other methods. In 2012, Nair et al. first discovered the ultrafast transport of water molecules in the interlayer channels of graphene oxide (GO) films, which provided a research basis for the rapid transport of ions in two-dimensional layered films [1]. After more than ten years of development, the types of two-dimensional layered materials used for ion separation have been greatly expanded. After studying the ion separation performance of two-dimensional layered films composed of many different types of materials, it was found that the selective transport of different ions in these films mainly comes from the interaction between ions and the size of the interlayer channels. For this reason, people have developed strategies such as ion intercalation, molecular crosslinking and partial reduction to regulate the size effect of the channels. However, the highest selectivity of monovalent / divalent ions obtained so far is only about 100.

[0004] [1]Nair RR,Wu HA,Jayaram PN,Grigorieva IV,Geim AKUNimpededpermeation of water through helium-leak-tight graphene-based membranes[J].Science,2012,335(6067):442-444. Summary of the Invention

[0005] The purpose of this invention is to prepare a two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations by controllingly coupling the size effect and charge effect based on the basic strategy of surface modification and by modifying the nanosheet material with appropriate functional groups. This membrane can be applied to ion separation in seawater, salt lakes or wastewater.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations is disclosed. The two-dimensional layered membrane is a membrane composed of stacked graphene oxide, wherein amino groups (-NH2) are grafted onto the inner walls of the channels within the membrane; the surface of the membrane is modified with carboxyl groups (-COOH), and high-valent cations are used to form coordination bonds with the carboxyl groups, thereby enabling the high-valent cations to act as gates and promote the membrane's selective separation of monovalent / high-valent cations.

[0008] Another object of the present invention is to provide the application of the aforementioned two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations in the selective separation of multivalent cations. The ultra-high selectivity for monovalent / multivalent cations described in this invention has a selectivity greater than 10,000.

[0009] In this invention, the two-dimensional layered film is preferably a film formed by stacking graphene oxide.

[0010] In this invention, the monovalent / multivalent cation includes K + Na + Mg 2+ Fe 3+ Mn 2+ And Al 3+ At least one of them.

[0011] Another object of the present invention is to provide a method for preparing a two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations, comprising the following steps:

[0012] Step 1: Graphene oxide (PGO) is dispersed in deionized water, and EDC is added and stirred. The carboxyl groups on the EDC and GO nanosheets form an O-acyl isourea intermediate that can react with amino groups. Then, polyethyleneimine (PEI) is added to the mixed solution and stirred. The O-acyl isourea intermediate forms an amide bond with PEI, releasing the isourea product. Subsequently, the mixed solution is dialyzed in a dialysis bag with stirring until the pH of the solution is neutral. The dialyzed solution is centrifuged to obtain a positively charged PGO nanosheet slurry.

[0013] Step 2: Stack the positively charged PGO nanosheet slurry obtained in Step 1 onto the substrate film to form a PGO film, and dry it to obtain a dried PGO film with a thickness of 0.5 μm to 4 μm.

[0014] Step 3: Immerse the dried PGO membrane obtained in Step 2 in a polyacrylic acid (PAA) solution to obtain a PGO-PAA membrane, which is a two-dimensional layered membrane with ultra-high monovalent / multivalent cation selectivity.

[0015] Step four: The PGO-PAA membrane is brought into contact with a solution containing high-valent cations, allowing the high-valent cations to form coordination bonds with carboxyl groups, thus obtaining a two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations.

[0016] In a preferred embodiment, in step one, the concentration of the GO solution dispersed in deionized water is (30-70) mg / 150 ml, and the volume ratio of EDC to GO solution is 1:(200-400).

[0017] In a preferred embodiment, in step one, the mass ratio of GO to polyethyleneimine is (30-70):1000.

[0018] In a preferred embodiment, in step one, the molecular weight of the polyacetylimide is 400 to 12000.

[0019] In a preferred embodiment, in step one, the dialysis bag cutoff size is 8000-14000.

[0020] In a preferred embodiment, in step two, the thickness of the PGO film is 0.5 μm to 4 μm.

[0021] In a preferred embodiment, in step two, a polyethersulfone (PES) microporous filter membrane is used as the base membrane.

[0022] In a preferred embodiment, the polyethersulfone (PES) microporous filter membrane has an average pore size of 0.2 μm to 0.3 μm and a porosity of 40% to 60%.

[0023] In a preferred embodiment, in step three, the molecular weight of the polyacrylic acid is 2000 to 30000.

[0024] In a preferred embodiment, in step three, the PGO membrane completely dried in step two is immersed in a polyacrylic acid (PAA) solution for 3-10 hours, and then the PAA-treated PGO membrane is vacuum dried at 40°C-60°C for 3-10 hours to ensure complete drying; it is then vacuum dried again at 70°C-80°C for 1-3 hours to obtain a PGO-PAA membrane; subsequently, the PGO-PAA membrane is fully immersed in deionized water to remove excess PAA molecules from the membrane surface; finally, the PGO-PAA membrane is vacuum dried again at 40°C-60°C for 6-18 hours to obtain a completely dried PGO-PAA membrane.

[0025] In a preferred embodiment, in step four, after the PGO-PAA membrane that has been completely dried in step three is assembled into the test cell, a solution containing high-valent cations (concentration of 0.05 mM to 0.1 M) is added to the test solution side to coordinate with the carboxyl functional groups on the membrane surface, thereby obtaining a two-dimensional layered membrane with ultra-high monovalent / multivalent cation selectivity.

[0026] This invention discloses a two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations, prepared by vacuum filtration of graphene oxide (GO) nanosheets. First, addressing the issue of instability in the interlayer channel structure caused by swelling of the GO membrane in solution, amino groups (-NH2) are grafted onto the inner walls of the channels. The hydrogen bonding interaction between amino groups and water molecules enhances its long-term stability in salt solutions, strong acids, and strong bases. Furthermore, by measuring the ion transport behavior in the GO membrane with a stable interlayer structure, rapid monovalent ion transport and significant trivalent cation interception were observed, with a selectivity greater than 4000 between monovalent and trivalent cations. Finally, by modifying the channel inlet with carboxyl groups (-COOH) that specifically interact with aluminum ions, and utilizing "high-valent cation gating such as aluminum ions," dynamic control of the channel surface charge density is achieved. This results in a final membrane with a monovalent / divalent cation selectivity exceeding 10000, two orders of magnitude higher than the existing best-performing membrane. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0028] Figure 1 (a) Schematic diagram of PGO nanosheet preparation process (b) AFM morphology and height diagram of PGO nanosheets.

[0029] Figure 2 (a) Optical photograph of PGO membrane with PES filter substrate (b) SEM image of cross-section of PGO membrane (c) K0 of PGO membrane at different thicknesses + / Mg 2+ and K + / Al 3+ Long-term stability test of selective (d)PGO membrane, K + And Al 3+ The permeation rate as a function of test time (the inset shows photographs of the PGO membrane at test days 0 and 201).

[0030] Figure 3 (a) Schematic diagram of the PGO-PAA membrane structure; (b) Zeta potential of the PGO-PAA membrane measured in Al3+ solutions of different concentrations (the blue dashed line represents the Zeta potential of the PGO-PAA membrane in the absence of Al3+, and the inset is a schematic diagram of charge reversal on the membrane surface); (c) Ka of the PGO-PAA membrane. + / Mg 2+ Selectivity and Al 3+ The concentration function (d) is used for continuous measurement of Al in high-concentration mixed salt solutions. 3+ Stability results of gated PGO-PAA films (e) with different metal ions in Fe 3+Selectivity (f) of different metal ions in gated PGO-PAA membranes in Mn 2+ Selectivity in gated PGO-PAA membranes.

[0031] Figure 4 (a) Different cations in Al 3+ Ion transport performance of gated PGO-PAA membrane, PEI covalently grafted with a molecular weight of 10000 (b) different cations in Al 3+ Ion transport performance of PGO-PAA membranes treated with gated high molecular weight PAA (Mw: 250000). Detailed Implementation

[0032] Example 1: Preparation of amino-covalently grafted graphene oxide nanosheets

[0033] 50 mg of GO solution was dispersed in 150 mL of deionized water and sonicated for 10 min. Then, 500 μL of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) was added and stirred for 1 h. In this step, EDC reacts with the carboxyl groups on the GO nanosheets to form an O-acylisourea intermediate that can react with amino groups. Then, 1 g of polyethyleneimine was added to the mixture and stirred for 3 h. The O-acylisourea intermediate forms an amide bond with PEI, releasing the isourea product. Subsequently, the mixture was dialyzed for 3 days in a dialysis bag (cutoff size 8000-14000) with stirring to remove excess EDC, PEI, and other small molecules until the solution pH was neutral. The dialyzed solution was centrifuged at 8000 rpm for 10 min to obtain a positively charged PGO (positive-GO) nanosheet slurry. The addition of PEI causes the PGO nanosheets to aggregate. To obtain monolayer PGO nanosheets, the PGO slurry was redispersed in deionized water and ultrasonically dispersed to obtain a homogeneous solution. Then, the obtained PGO solution was centrifuged at 6000 rpm for 10 min to remove the thick PGO nanosheets, resulting in a solution with a monolayer PGO nanosheet dispersion.

[0034] Example 2: Preparation and Ion Separation Performance of Amino-Grafted Stable Graphene Oxide Membranes

[0035] During water permeation and ion permeation experiments, to ensure the integrity of the PGO membrane and prevent it from easily detaching from the substrate, we selected a hydrophilic polyethersulfone (PES) microporous filter membrane. The oxygen in PES forms hydrogen bonds with the oxygen-containing functional groups in PGO, ensuring that the PGO membrane filtered using the PES filter does not detach from the substrate even after complete drying. The PES filter membrane has a diameter of 25 mm, an average pore size of 0.22 μm, and a porosity of approximately 50%. 0.5 mg of PGO solution was dispersed in deionized water and stirred for 0.5 h. The PGO solution was added to the upper filter cup, and a vane pump was used to evacuate the filter flask below the PES filter membrane. After the solution in the upper filter cup was completely filtered into the lower filter flask, PGO nanosheets larger than the pore size of the PES filter membrane stacked under the vacuum force to form a PGO membrane. The PGO membrane was then dried in a vacuum oven at 50 °C for 12 h to obtain a completely dried PGO membrane. Figure 2 As shown in (a). This PGO membrane is effective against K. + / Al 3+ and K + / Mg 2+ The relationship between selectivity and film thickness is as follows: Figure 2 As shown in (c), the ion selectivity is highest at a thickness of 4 μm (K). + / Al 3+ >4000). Meanwhile, after approximately 200 days of testing, the PGO membrane... + And Al 3+ The permeation rate remained stable, and K + / Al 3+ Selective variation less than 10%, results as follows Figure 2 As shown in (d).

[0036] Example 3: Preparation and Ion Separation Performance of Carboxyl- and Cation-Modified Graphene Oxide Membranes with Tunable Charge Density

[0037] The completely dried PGO membrane was immersed in a polyacrylic acid (PAA) solution (Mw = 3000) for 6 hours, and then the PAA-treated PGO membrane was vacuum dried at 50°C for 4 hours to ensure complete drying. To further enhance the interaction between the PAA and PGO membranes, it was vacuum dried again at 75°C for 2 hours to obtain a PGO-PAA membrane. Next, the PGO-PAA membrane was thoroughly immersed in deionized water to remove excess PAA molecules from the membrane surface. Finally, the PGO-PAA membrane was vacuum dried again at 50°C for 12 hours to obtain a completely dried PGO-PAA membrane. Due to Al... 3+ It will coordinate with the carboxyl groups in the PGO-PAA membrane (e.g. Figure 3As shown in a), and it will be completely retained during the permeation process, thus it can affect the transport of other ions by adjusting the channel size and charge effect. Therefore, a certain concentration of Al is added to the feed side. 3+ It can be used as a gated ion, such as Figure 3 As shown in (b), the surface charge density of the PGO-PAA film is dynamically controlled by utilizing changes in its concentration. Figure 3 As shown in (c), with the addition of Al 3+ The effect of concentration changes on the K+ ion exchange rate of the PGO-PAA membrane. + / Mg 2+ The selectivity can reach up to approximately 12,000, exceeding the best existing films by two orders of magnitude. For practical applications, the cycling stability of the membrane is crucial; therefore, the stability of the PGO-PAA membrane was tested in a 2M high-concentration mixed salt solution. The results are as follows: Figure 3 As shown in (d), after 15 days of testing, Li + / Mg 2+ The selectivity remains greater than 3000, far exceeding that of current ion-selective membrane materials. Furthermore, the gated ions used to regulate the surface charge density of membrane channels are not limited to Al. 3+ It can also be extended to Fe 3+ and Mn 2+ Ions. Using Fe 3+ and Mn 2+ When ions coordinate with PAA, such as Figure 3 (e) and Figure 3 As shown in (f), K + / Mg 2+ The selectivity can reach levels of >900 and >30, respectively.

[0038] Example 4: Expandable molecular weight range of amino and carboxyl polymers for modifying graphene oxide two-dimensional film devices

[0039] In this embodiment, PEI with molecular weights of 600 and 10000 were covalently grafted onto GO to prepare PGO membranes, and their separation selectivity for monovalent / polyvalent cations was then tested. The results are as follows: Figure 4 As shown in (a), the selectivity for monovalent / divalent ions decreases by approximately one order of magnitude as the molecular weight of PEI increases from 600 to 10,000. This is because the increased molecular weight of PEI results in a greater abundance of amino functional groups grafted onto the channel wall, allowing for the adsorption of more PAA and Al. 3+ This reduces the permeation rate of monovalent ions. However, at the same time, higher molecular weight PEI can increase the interlayer channel size of the PGO membrane, thus reducing the Mg content. 2+ The electrostatic repulsion caused by the Mg 2+The increased permeation rate eventually led to a decrease in the selectivity for monovalent / divalent ions. Even so, the reduced selectivity for monovalent / divalent ions was still superior to the currently reported membrane performance. For PAA, which acts as a carboxyl-modifying agent, the molecular weight was also increased from 3000 to 250000. Since PAA is modified on the surface of the PGO membrane, the increase in its molecular weight did not affect the membrane channel size, i.e., it did not affect the sieving performance of monovalent / divalent ions (results are shown in...). Figure 4 (b) is shown.

[0040] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing a two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations, comprising the following steps: Step 1: Graphene oxide is dispersed in deionized water, and then 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) is added and stirred. The EDC and the carboxyl groups on the graphene oxide nanosheets form an O-acyl isourea intermediate that can react with amino groups. Then, polyethyleneimine is added to the mixed solution and stirred. The O-acyl isourea intermediate forms an amide bond with polyethyleneimine, and the isourea product is released at the same time. Subsequently, the mixed solution was dialyzed in a dialysis bag with stirring until the pH of the solution was neutral; the dialyzed solution was centrifuged to obtain positively charged PGO nanosheet slurry; Step 2: Stack the positively charged PGO nanosheet slurry obtained in Step 1 onto the substrate membrane to form a PGO membrane, and then dry it to obtain the dried PGO membrane. Step 3: Immerse the dried PGO membrane obtained in Step 2 in a polyacrylic acid (PAA) solution to obtain a PGO-PAA membrane; Step four: The PGO-PAA membrane is brought into contact with a solution containing high-valent cations, allowing the high-valent cations to form coordination bonds with carboxyl groups, thus obtaining a two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations.

2. The method for preparing a two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations according to claim 1, characterized in that: In step one, the concentration of GO solution dispersed in deionized water is (30~70) mg / 150 ml, the volume ratio of EDC to GO solution is 1:(200~400), and the mass ratio of graphene oxide to polyethyleneimine is (30~70):1000.

3. The method for preparing a two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations according to claim 1, characterized in that: In step one, the molecular weight of polyacetylimide is 400~12000.

4. The method for preparing a two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations according to claim 1, characterized in that: In step three, the molecular weight of polyacrylic acid is 2000~30000.

5. The method for preparing a two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations according to claim 1, characterized in that: In step three, the PGO membrane that was completely dried in step two is immersed in a polyacrylic acid (PAA) solution for 3 h to 10 h, and then the PAA-treated PGO membrane is vacuum dried at 40℃ to 60℃ for 3 h to 10 h to make the membrane completely dry. The membrane was then vacuum dried at 70℃~80℃ for 1h~3h to obtain a PGO-PAA membrane. After that, the PGO-PAA membrane was fully immersed in deionized water to remove excess PAA molecules from the membrane surface. Finally, the PGO-PAA membrane was vacuum dried again at 40℃~60℃ for 6h~18h to obtain a completely dry PGO-PAA membrane.

6. The method for preparing a two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations according to claim 1, characterized in that: In step four, the high-valence cation is Al. 3+ Fe 2+ or Mn 2+ The concentration range of the high-valence cation is 0.05 mM to 0.1 M.

7. A two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations, characterized in that: The inner wall of the channel within the two-dimensional layered membrane is grafted with amino groups; carboxyl groups are modified on the surface of the membrane, and high-valent cations are used to form coordination bonds with the carboxyl groups, thereby enabling the high-valent cations to act as gates and promote the membrane's selective separation of monovalent / high-valent cations; the two-dimensional layered membrane is prepared according to the method described in claim 1.

8. The two-dimensional layered membrane with ultra-high selectivity for monovalent / multivalent cations according to claim 7, characterized in that: The two-dimensional layered film is a film made of stacked graphene oxide.

9. The application of a two-dimensional layered membrane with ultra-high selectivity for monovalent / polyvalent cations as described in any one of claims 7 or 8 in the selective separation of polyvalent cations.

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