A lithium ion selective transport membrane and its preparation method and application

Abstract

The application provides a lithium ion selective transmission membrane and a preparation method thereof, wherein a group activator 1-ethyl-(3-dimethylamino propyl) carbonyl diimide is dispersed into a graphene oxide dispersion solution to uniformly stir and activate carboxyl groups on the surface of nanosheets; then, a polymer with an amine group is added to uniformly stir and disperse, dialysis is performed, and a dispersion solution of amine-functionalized graphene oxide nanosheets is obtained; the dispersion solution is assembled on a porous membrane through a pressure-driven vacuum filtration method, and is dried, so that the lithium ion selective transmission membrane is obtained. Through micro-modification of graphene oxide two-dimensional nanosheets, the two-dimensional channels stacked by the graphene oxide two-dimensional nanosheets have a large number of uniform positive charges, transmission of divalent ions such as magnesium ions can be effectively prevented while stable lithium ion transmission is maintained, high permeability and high selectivity are exhibited in a mixed system of lithium ions and magnesium ions, and the lithium ion selective transmission membrane can be used in related fields such as lithium extraction from salt lake brine.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of membrane separation, and particularly relates to a lithium ion selective transport membrane and a preparation method and application thereof. BACKGROUND

[0002] Lithium is widely used in lithium ion batteries, ceramics, lubricants and other fields due to its excellent electrochemical activity, high specific heat capacity and low expansion rate (J. Am. Chem. Soc. 2002, 124, 4936-4937.; J. Phys. Chem. Lett. 2022, 13, 11307-11316.; Appl. Surf. Sci. 2022, 579, 152161.). In recent years, with the development of the electronic product industry, the demand for lithium ion batteries has increased significantly (J. Membr. Sci. 2016, 510, 141-154.; Appl. Energy 2013, 110, 252-266.). Generally, lithium mainly exists in two resources: lithium-containing minerals and lithium-containing water. It is reported that the lithium resources in salt lakes and seawater account for more than 60% of the total lithium resources in the world. However, due to the presence of high content of ions with similar size and properties such as potassium, sodium, calcium and magnesium in salt lake brine or seawater, it is extremely difficult to recover lithium (Sep. Purif. Technol. 2022, 286, 120419.; Mater. Chem. Phys. 2014, 148, 548-553.). At present, there are many methods for extracting lithium from brine or seawater, such as adsorption, precipitation, electrodialysis and the like, but they have problems such as high energy consumption, low efficiency and environmental unfriendliness (Angew. Chem., Int. Ed. 2016, 55, 15120-15124.).

[0003] Membrane technology is an effective method for extracting lithium from salt water or seawater, which has attracted more and more attention due to its low energy consumption and environmental friendliness (Nat. Commun. 2019, 10, 1253.). Polymer materials are usually used as ordinary commercial membranes due to their low cost and easy industrialization. However, it is generally difficult for traditional polymer membranes to achieve precise pore size regulation at the sub-nanometer scale, resulting in challenges in separating lithium from aqueous solutions containing multiple coexisting ions. Therefore, it is of great significance to research and develop a new type of lithium ion selective transport membrane. SUMMARY

[0004] The present application aims to overcome the deficiencies in the prior art, solve the problem of low transmission and separation efficiency of lithium ions in the separation membrane, and provide a uniform positively charged two-dimensional graphene oxide membrane with lithium ion selective transmission performance and a preparation method thereof.The present application activates the surface carboxyl groups of graphene oxide using 1-ethyl-(3-dimethylaminopropyl) carbodiimide, then modifies the amine groups on the surface of graphene oxide through covalent interaction and electrostatic interaction, and prepares a membrane on a substrate under the action of pressure-driven vacuum filtration to obtain a graphene oxide membrane supported by a substrate.The graphene oxide membrane can effectively prevent the transmission of divalent ions such as magnesium ions while maintaining stable lithium ion transmission, and exhibits high permeability and high selectivity in a mixed system of lithium ions and magnesium ions.

[0005] The technical scheme adopted by the present application is as follows: a preparation method of a lithium ion selective transmission membrane, comprising the following steps:

[0006] (1) Activation of graphene oxide nanosheets: disperse group activator 1-ethyl-(3-dimethylaminopropyl) carbodiimide (EDC) into a graphene oxide dispersion liquid and stir uniformly; the graphene oxide dispersion liquid is a suspension of single-atom layered graphene oxide nanosheets;

[0007] (2) Amine modification of graphene oxide nanosheets: add a polymer with amine groups to the activated graphene oxide dispersion liquid, stir and disperse uniformly, and dialyze to obtain an amine-modified graphene oxide nanosheet dispersion liquid;

[0008] (3) Preparation of positively charged graphene oxide membrane: assemble the amine-modified graphene oxide nanosheets on a porous membrane by pressure-driven vacuum filtration, and dry to obtain the lithium ion selective transmission membrane.

[0009] The present application is further provided that the graphene oxide dispersion liquid in step (1) is prepared by a modified Hummers method. Specifically, the modified Hummers method is as follows:

[0010] Mix potassium persulfate, phosphorus pentoxide and concentrated sulfuric acid, heat to 78-82 DEG C, then mix with natural graphite, heat, cool to room temperature, dilute with deionized water, stand for 12-18h, filter and dry to complete the pre-oxidation of graphite; mix the pre-oxidized product with concentrated sulfuric acid at 0-5 DEG C, then react with potassium permanganate at 34-36 DEG C for 1.5-2.5h, then react with hydrogen peroxide to obtain a mixture, complete the oxidation and layer peeling of the graphite; wash, filter and ultrasonic the mixture to obtain the graphene oxide dispersion liquid.

[0011] The application is further provided that the graphene oxide dispersion in step (1) is a suspension of graphene oxide nanosheets with single-atom layers and an average layer size of about 5 μm (5±1 μm).

[0012] The application is further provided that the concentration of the graphene oxide dispersion in step (1) is 2-5 mg / mL. A lower concentration of graphene oxide reduces the efficiency of film preparation, while a higher concentration affects the dispersibility of the nanosheets in the dispersion, resulting in an uneven film.

[0013] The application is further provided that the ratio of the added amount of EDC to graphene oxide (μL / mg) in step (1) is (0.5-2):1.

[0014] The application is further provided that the amine group-containing polymer in step (2) is selected from one or more of polyethyleneimine (PEI), polyacrylamide (PAM), and polyallylamine (PAH).

[0015] The application is further provided that the molecular weight of the amine group-containing polymer in step (2) is 600-70,000, preferably 600-10,000, and more preferably 10,000. A higher molecular weight of the amine group-containing polymer has a higher density of positively charged amine groups, but when the positive charge is too high, the electrostatic effect will simultaneously repel lithium ions, reducing the lithium ion transmission efficiency of the target film.

[0016] The application is further provided that the mass ratio of the added amount of the amine group-containing polymer to graphene oxide in step (2) is (0.5-4):1, and preferably (0.5-2):1. A higher content of the amine group-containing polymer in the graphene oxide nanochannel increases the positive charge of the channel, but an excessive amount of the amine group-containing polymer will simultaneously occupy the channel space, hindering the transmission of lithium ions.

[0017] The application is further provided that the stirring in steps (1) and (2) is magnetic stirring, the speed of which is 600-1200 r / min, the stirring time in step (1) is 0.5-2 h, and the stirring time in step (2) is 3-5 h, and preferably 4 h. Appropriate stirring is conducive to the dissolution of the group activating agent and the amine group-containing polymer molecular chain, and the full contact with the graphene oxide nanosheets, while excessive stirring will affect the structure and performance of the nanosheets.

[0018] The application is further provided that the molecular weight of the dialysis bag in the dialysis process of step (2) is 600-14,000 Da, and the dialysis time is 5-7 days.

[0019] The application is further provided that the porous membrane in step (3) can provide sufficient mechanical support for the graphene oxide membrane, and the material is selected from one of mixed cellulose ester, nylon, polyacrylonitrile and polycarbonate.

[0020] The application is further provided that the average pore size of the porous membrane in step (3) is 0.1-0.22 μm, and the pore size that is too small will bring too high transmission resistance, and the pore size that is too large will reduce the mechanical support force, so that the mechanical strength of the graphene oxide membrane is low.

[0021] The application is further provided that the driving pressure of the vacuum filtration in step (3) is 0.1-0.5 Mpa, and the pressure that is too low will make the laminated membrane structure of the graphene oxide membrane loose and the mechanical strength low, and the pressure that is too high will make the laminated membrane structure too tight, which is not conducive to ion transmission.

[0022] The application is further provided that the drying temperature in step (3) is 25-60℃, and the drying time is 12-36 h. The drying process can remove the water in the membrane, so that the membrane structure is more compact, the drying temperature that is too low will reduce the membrane preparation efficiency, and the drying temperature that is too high will remove the oxygen-containing functional groups on the surface of the graphene oxide and damage the membrane structure.

[0023] The second aspect of the application is to provide a lithium ion selective transmission membrane prepared by the above preparation method of the lithium ion selective transmission membrane with lithium ion selectivity, the lithium ion selective transmission membrane is a graphene oxide membrane with a positively charged two-dimensional channel, and includes a porous membrane base film and an amine-based graphene oxide nanosheet deposition layer.

[0024] The third aspect of the application is to provide the application of the above lithium ion selective transmission membrane, which is used for lithium-magnesium separation in a mixed system of lithium ions and magnesium ions, and specifically used for lithium extraction in salt lake brine. The maximum selectivity of lithium-magnesium of the lithium ion selective transmission membrane is 22.2, and at this time, the flux of lithium ions is 0.09 mol·m -2 h -1 .

[0025] In the technical scheme of the application, the amine group with positive electricity is grafted to the surface of the graphene oxide nanosheet after the surface carboxyl group of the graphene oxide nanosheet is activated by EDC, and a two-dimensional nanochannel with positive electricity is further constructed by using a vacuum filtration method. Compared with the prior art, the application has the beneficial effects that:

[0026] (1) After EDC activation, the amine groups are grafted on the surface of the nanosheet, which not only provides positive charges for the two-dimensional nanochannel and changes the electrical characteristics of the graphene oxide nanochannel, but also effectively reduces the swelling of the membrane in aqueous solution and effectively controls the interlayer spacing, while improving the stability of the membrane. Based on the charge difference between monovalent lithium ions and divalent magnesium ions and the size difference of hydrated ions, the graphene oxide two-dimensional nanomembrane with fixed interlayer spacing and amine group modification with positive electric characteristics shows high lithium ion transmission efficiency and high magnesium lithium selectivity.

[0027] (2) Using graphene oxide as raw material can realize the adjustment of the micro-pore size of the separation membrane, which can solve the problem of difficult adjustment of the pore size in traditional membranes and expand the use range of new two-dimensional membranes. By controlling the surface properties of graphene oxide nanosheet at the microscale, the effective adjustment of the stacked two-dimensional channel is realized. The graphene oxide two-dimensional membrane prepared by the above method has more uniform pore channels and stable structure, which solves the problem of non-uniform pore channels and unstable structure in the method of macroscopic control of membranes.

[0028] (3) The above preparation method is simple and easy to operate, and the prepared membrane has the characteristics of high mechanical strength and stable structure, can selectively transport lithium ions, and has a hindering effect on the transmission of magnesium and other divalent ions, has high ion sieving performance, and has good application prospect in lithium extraction from salt lake brine and other aspects. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 TEM morphology and element distribution map of amine-modified graphene oxide nanosheet prepared in Example 1;

[0030] Figure 2 Zeta potential map of amine-modified graphene oxide solution prepared in Example 1 and original graphene oxide solution;

[0031] Figure 3 SEM surface and cross-sectional morphology map of polyethyleneimine grafted graphene oxide membrane prepared in Example 1;

[0032] Figure 4 XRD characterization comparison map of polyethyleneimine grafted graphene oxide membrane prepared in Example 1 and graphene oxide membrane prepared in Comparative Example 1;

[0033] Figure 5 Separation performance of polyethyleneimine grafted graphene oxide membranes with different molecular weights prepared in Example 1 and Examples 2-4 in magnesium-lithium separation test;

[0034] Figure 6are the separation performances of graphene oxide membranes prepared in Example 1 and Examples 5-7 with different ratios of grafted polyethyleneimine in magnesium-lithium separation tests.

[0035] Figure 7 are the separation performances of graphene oxide membranes prepared in Example 1 and Comparative Examples 1-2 in magnesium-lithium separation tests. DETAILED DESCRIPTION

[0036] The technical solutions of the present application are described below in specific embodiments. It should be understood that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of the present application.

[0037] Example 1

[0038] (1) Preparation of group-activated graphene oxide nanosheets

[0039] A graphene oxide dispersion solution was prepared by a modified Hummers method and diluted with deionized water to 2 mg / mL.

[0040] 50 mL of the graphene oxide dispersion solution was taken, 200 μL of group-activating agent 1-ethyl-(3-dimethylaminopropyl) carbodiimide (EDC) was added, and magnetic stirring was carried out at room temperature at a speed of 1000 r / min for 1 h to ensure sufficient mixing and uniformity.

[0041] (2) Amine-modified graphene oxide nanosheets (GO-PEI)

[0042] A polyethyleneimine solution with a molecular weight of 10000 was added to the group-activated graphene oxide nanosheet dispersion solution, and the amount of polyethyleneimine added was 0.2 g. The stirring was continued at the same speed for 4 h at room temperature. The dispersion solution with sufficient mixing and uniform grafting was transferred to a dialysis bag with a molecular weight of 10000, and dialysis was carried out for 7 days to remove the ungrafted polyethyleneimine molecular chains.

[0043] The amine-grafted graphene oxide nanosheets obtained were observed for morphology, and the TEM image and element distribution map are shown in Figure 1 As can be seen from the figure, in the grafted nanosheet layer, in addition to the elements such as carbon and oxygen contained in the graphene oxide nanosheet itself, the nitrogen element is also uniformly distributed on the surface. The nitrogen element comes from the amine group on the polyethyleneimine molecular chain, indicating that the amine group has been uniformly grafted to the surface of the graphene oxide nanosheet.

[0044] The zeta potential of the amine-grafted graphene oxide nanosheet dispersion solution was further tested, as shown in Figure 2The dispersion solution shows positive zeta potential at different pH values. Compared with the negative zeta potential of graphene oxide dispersion solution, it is further proved that the positively charged amine groups have been successfully grafted on the surface of nanosheets.

[0045] (3) Preparation of positively charged two-dimensional graphene oxide membrane

[0046] The graphene oxide dispersion solution with grafted amine groups was diluted 20 times and ultrasonicated at 700 W for 30 min. 6 mL of the uniform dispersion solution was taken and further diluted to 50 mL with deionized water. The dispersion solution was filtered on a mixed cellulose ester substrate with a pore size of 0.22 μm. Finally, the membrane with substrate support was placed in an oven at 60°C and dried for 12 h to obtain the graphene oxide membrane.

[0047] The surface morphology and cross-section of the obtained target membrane were observed, and the SEM image is shown in Figure 3 The surface has obvious wrinkles, which is a basic feature of graphene oxide-based membranes, and the fault thickness is about 300 nm.

[0048] The membrane after the amine molecular chain grafting was further tested by X-ray diffraction (XRD), as shown in Figure 4 The results show that under dry conditions, the interlayer spacing of the membrane is expanded to from the original graphene oxide membrane , and under wet conditions, it is reduced to from the original graphene oxide membrane The introduction of polyethyleneimine molecular chains significantly expands the two-dimensional channel of graphene oxide under dry conditions, and effectively prevents the swelling of the channel under wet conditions.

[0049] (4) Test of magnesium / lithium separation performance of positively charged graphene oxide membrane

[0050] The above prepared membrane with substrate support was cut to the appropriate size and sealed into a self-made U-shaped permeation device. A mixed solution of 0.1 mol / L magnesium chloride and lithium chloride was added to one side of the permeation cell, and deionized water was added to the other side. During the free permeation process, magnetic stirring was carried out on both sides. After 8 h of free permeation, the permeate on the side of deionized water was taken, and the ion concentration was tested, and the lithium ion permeation rate and lithium / magnesium ion selectivity were further calculated. Specifically, the lithium ion permeation rate is 0.09 mol·m -2 h -1 , and the lithium / magnesium ion selectivity is 22.2.

[0051] Example 2

[0052] The preparation method is the same as that of Example 1, except that the molecular weight of the polyethyleneimine used is 600 and the molecular weight of the dialysis bag is 600. In the magnesium / lithium separation performance test, the permeation rate of lithium ions is 0.14 mol·m -2 h -1 and the lithium / magnesium selectivity is 13.8.

[0053] Example 3

[0054] The preparation method is the same as that of Example 1, except that the molecular weight of the polyethyleneimine used is 1800 and the molecular weight of the dialysis bag is 1800. In the magnesium / lithium separation performance test, the permeation rate of lithium ions is 0.12 mol·m -2 h -1 and the lithium / magnesium selectivity is 17.4.

[0055] Example 4

[0056] The preparation method is the same as that of Example 1, except that the molecular weight of the polyethyleneimine used is 70000 and the molecular weight of the dialysis bag is 70000. In the magnesium / lithium separation performance test, the permeation rate of lithium ions is 0.08 mol·m -2 h -1 and the lithium / magnesium selectivity is 9.4.

[0057] Example 5

[0058] The preparation method is the same as that of Example 1, except that the amount of polyethyleneimine added is 0.05 g. In the magnesium / lithium separation performance test, the permeation rate of lithium ions is 0.16 mol·m -2 h -1 and the lithium / magnesium selectivity is 9.2.

[0059] Example 6

[0060] The preparation method is the same as that of Example 1, except that the amount of polyethyleneimine added is 0.10 g. In the magnesium / lithium separation performance test, the permeation rate of lithium ions is 0.13 mol·m -2 h -1 and the lithium / magnesium selectivity is 16.8.

[0061] Example 7

[0062] The preparation method is the same as that of Example 1, except that the amount of polyethyleneimine added is 0.40 g. In the magnesium / lithium separation performance test, the permeation rate of lithium ions is 0.02 mol·m -2 h -1 and the lithium / magnesium selectivity is 6.8.

[0063] Example 8 Magnesium / lithium separation performance test in simulated brine

[0064] The preparation method is the same as that of Example 1, and a positively charged two-dimensional graphene oxide film (GO-PEI) with a thickness of about 2 μm is prepared. The reverse osmosis separation experiment is carried out by using a simulated brine mixed solution with a high magnesium / lithium ratio (the magnesium concentration is 1866 mg / L, the lithium concentration is 134 mg / L, and the magnesium / lithium ratio is about 13.9). Under the pressure driving of 0.1 MPa, the lithium permeation rate is 0.82 mol·m -2 h -1 , and the lithium / magnesium selectivity is 8.2. Compared with the forward osmosis system, although the lithium / magnesium selectivity decreases, the lithium transmission rate is greatly improved due to the pressure driving, and the comprehensive performance is excellent.

[0065] Comparative Example 1

[0066] (1) Preparation of graphene oxide dispersion

[0067] The graphene oxide dispersion is prepared by a modified Hummers method, and is diluted to 0.1 mg / mL with deionized water. 6 mL is taken and further diluted to 50 mL, and a uniform graphene oxide dispersion is obtained by ultrasonic treatment at 700 W for 30 min.

[0068] (2) Preparation of graphene oxide film

[0069] The graphene oxide dispersion is suction filtered on a mixed cellulose ester substrate with a pore size of 0.22 μm. Finally, the film with substrate support is placed in an oven at 60°C and dried for 12 h to obtain the graphene oxide film with substrate support.

[0070] (3) Test of magnesium / lithium separation performance of graphene oxide film

[0071] The film with substrate support prepared above is cut to an appropriate size and sealed into a self-made U-shaped osmotic device. A mixed solution of 0.1 mol / L magnesium chloride and lithium chloride is added to one side of the osmotic cell, and deionized water is added to the other side. During the free osmosis process, magnetic stirring is carried out on both sides. After 8 h of free osmosis, the permeate on the deionized water side is taken, and the ion concentration is tested, and the lithium ion permeation rate and the lithium / magnesium ion selectivity are further calculated. Specifically, the lithium ion permeation rate is 0.21 mol·m -2 h -1 , and the lithium / magnesium ion selectivity is 1.7.

[0072] Comparative Example 2

[0073] The preparation method is the same as that of Example 1, except that when preparing the amine-modified nanosheets, the pH of the graphene oxide dispersion liquid is adjusted to 11, no group activator 1-ethyl-(3-dimethylaminopropyl) carbodiimide (EDC) is added, and a corresponding amount of polyethyleneimine is directly added.

[0074] It is found that the prepared amine-modified nanosheets have slight agglomeration, indicating that the polyethyleneimine is not uniformly distributed. In the magnesium / lithium separation performance test, the permeation rate of lithium ions is 0.62 mol·m -2 h -1 and the lithium / magnesium selectivity is 2.1, as shown in the following table. Figure 7 The high lithium transport rate and low magnesium / lithium selectivity are caused by a large number of defects in the film caused by the non-uniformly dispersed agglomerated nanosheets. The addition of EDC in Example 1 activates the surface of the nanosheets, which is beneficial to the uniform dispersion of the amino-modified graphene nanosheets and improves the magnesium / lithium selectivity of the positively charged two-dimensional graphene oxide film.

[0075] The present application is described in detail, which is intended to enable those skilled in the art to understand and implement the content of the present application, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and principle of the present application should be covered within the protection scope of the present application.

Claims

1. A production method of a lithium ion-selective transport membrane for lithium-magnesium separation in a mixed system of lithium ions and magnesium ions, characterized by, The method comprises the following steps: (1) dispersing a group activator 1-ethyl-(3-dimethylaminopropyl) carbodiimide into a graphene oxide dispersion liquid, which is a suspension of single-atom-layer graphene oxide nanosheets, and stirring uniformly; (2) adding an amine group-containing polymer into the activated graphene oxide dispersion liquid, stirring and dispersing uniformly, and dialyzing to obtain a dispersion liquid of amine group-modified graphene oxide nanosheets; (3) assembling the amine group-modified graphene oxide nanosheets on a porous membrane through a pressure-driven vacuum filtration method, and drying to obtain the lithium ion-selective transport membrane. In step (2), the amine group-containing polymer is selected from one or more of polyethyleneimine, polyacrylamide, and polyallylamine, has a molecular weight of 600-10,000, and has a mass ratio of 0.5-2:1 to the added amount of graphene oxide.

2. The method for producing a lithium ion-selective transport membrane according to claim 1, characterized by, In step (1), the graphene oxide dispersion liquid is a suspension of single-atom-layer graphene oxide nanosheets with an average sheet size of 5±1 μm, which is prepared by a modified Hummers method.

3. The method of claim 1, wherein the lithium ion-selective transport membrane is prepared by the steps of: (a) preparing a solution of a lithium ion-selective membrane material; (b) coating the solution onto a substrate; and (c) drying the solution to form the lithium ion-selective transport membrane. In step (1), the concentration of the graphene oxide dispersion liquid is 2-5 mg / mL.

4. The method for producing a lithium ion-selective transport membrane according to claim 1, wherein In step (1), the ratio of the added amount of 1-ethyl-(3-dimethylaminopropyl) carbodiimide to graphene oxide is 0.5-2 μL:1 mg.

5. The method for preparing a lithium-ion selective transport membrane according to claim 1, characterized in that, In step (3), the porous membrane is used as a support substrate and is made of one of mixed cellulose ester, nylon, polyacrylonitrile, and polycarbonate.

6. The method for preparing a lithium-ion selective transport membrane according to claim 5, characterized in that, In step (3), the average pore size of the porous membrane is 0.1-0.22 μm, and the driving pressure of the vacuum filtration is 0.1-0.5 MPa.

7. The method for preparing a lithium-ion selective transport membrane according to claim 1, characterized in that, In step (3), the drying temperature is 25-60 °C, and the drying time is 12-36 h.

8. A lithium ion-selective transport membrane, characterized by, The method for preparing the lithium ion-selective transport membrane according to any one of claims 1-7 is used to prepare a graphene oxide membrane with a positive charge two-dimensional channel, which comprises a porous membrane base film and a deposited layer of amine group-modified graphene oxide nanosheets.

9. Use of the lithium ion-selective transport membrane according to claim 8, characterized in that Lithium-magnesium separation in a mixed system of lithium ions and magnesium ions.

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