A heterogeneous membrane with different functionalized channels and its preparation method and application

Abstract

The application provides a heterogeneous membrane with different functional channels and a preparation method thereof, and the heterogeneous membrane comprises a base membrane and a double-sided graphene oxide membrane deposited on one side surface of the base membrane, wherein the double-sided graphene oxide membrane is sequentially deposited by amine group functionalized graphene oxide nanosheets and sulfonic acid group functionalized graphene oxide nanosheets by a vacuum filtration method. By changing the group type and distribution in the graphene oxide nanochannel, the application constructs a superimposed heterogeneous layer with ion rapid transmission function and lithium-magnesium high-efficiency separation function, and can effectively prevent magnesium ions from passing through while rapidly transmitting lithium ions, so that high-efficiency separation of lithium and magnesium is realized, and the application has a wide application prospect in the field of lithium extraction from salt lake brine and the like.

Description

Technical Field

[0001] This invention belongs to the technical field of membrane separation, specifically, it relates to a heterogeneous membrane with different functionalized channels, its preparation method and application. Background Technology

[0002] Lithium is the lightest known alkali metal in nature, hailed as a "high-energy metal" and an "energy metal that drives technological progress." It has wide applications in lithium batteries, ceramics, glass, metallurgy, and chemicals. In recent years, with the development of technology, the global demand for metallic lithium has been continuously increasing.

[0003] Lithium resources are mainly found in lithium-containing minerals and salt lake brines. Salt lake brines account for approximately 60% of the Earth's total lithium content and are considered the primary source of lithium resources. However, the concentration of lithium ions in most salt lake brines is extremely low, and they are often mixed with other alkali metal ions, especially magnesium ions. The magnesium-to-lithium ratio in salt lake brines is very high, and the hydration radii of magnesium and lithium ions are very similar, making the separation and extraction of lithium from salt lake brines extremely difficult. Existing methods for lithium extraction from salt lakes mainly include solvent extraction, salting out, precipitation, and ion exchange, but these methods still face many challenges in practical applications due to limitations in process complexity and low efficiency.

[0004] Membrane separation has attracted increasing attention due to its advantages such as low cost, high efficiency, and ease of operation. Most existing membrane separation technologies are based on size sieving effects. However, because magnesium and lithium ions have very similar hydration diameters, precisely controlling the membrane pore size to achieve efficient magnesium-lithium separation is extremely difficult. Furthermore, some studies have used positively charged membranes, utilizing the electrostatic repulsion difference between the membrane and magnesium-lithium ions to achieve magnesium-lithium separation. However, since lithium ions are also positively charged, a single positively charged channel inevitably leads to lithium ion loss, reducing lithium ion transport performance and weakening the magnesium-lithium separation effect.

[0005] Therefore, developing a novel membrane channel with rapid lithium-ion transport and high-efficiency magnesium-lithium separation is urgently needed for lithium extraction from salt lake brine. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and address the problems of low lithium-ion transport efficiency and magnesium-lithium separation efficiency in separation membranes, providing a simple and easy method for preparing heterogeneous membranes with different functional channels. This invention uses graphene oxide nanosheets as the base material for modification. The nanosheet surfaces are modified by amination and sulfonation, respectively. The modified nanosheets are then sequentially loaded onto a polymer porous membrane using vacuum filtration to prepare heterogeneous membranes with different functionalized channels. The negative charge in the two-dimensional channels formed by stacking sulfonated graphene oxide nanosheets is beneficial for lithium-ion introduction, and the low affinity of sulfonated groups for lithium ions facilitates rapid lithium-ion transport, thus forming a lithium-ion transport layer. The positive charge in the two-dimensional nanochannels formed by stacking amination-modified graphene oxide nanosheets is beneficial for magnesium-lithium separation, forming a separation layer. By adjusting the group density of different functional layers, both the lithium-ion transport rate and the magnesium-lithium separation efficiency can be improved simultaneously.

[0007] The technical solution adopted in this invention is as follows:

[0008] A heterogeneous membrane with different functionalized channels, the heterogeneous membrane comprising a base membrane and a double-sided graphene oxide membrane deposited on one side surface of the base membrane, the double-sided graphene oxide membrane comprising graphene oxide nanosheets modified by amine functionalization and graphene oxide nanosheets modified by sulfonic acid functionalization sequentially deposited on the base membrane.

[0009] The present invention is further configured such that the thickness of the double-sided graphene oxide film is 200-1000 nm, preferably 400-600 nm.

[0010] The present invention is further configured such that the mass ratio of the graphene oxide nanosheets modified by amine functionalization to the graphene oxide nanosheets modified by sulfonic acid functionalization is (0.5-2):1.

[0011] The present invention is further configured such that the base film is a porous polymer film, which serves as a supporting substrate and can provide sufficient mechanical support for the double-sided graphene oxide film. The material is selected from one of the following: mixed cellulose ester, nylon, polyacrylonitrile, polycarbonate, etc. The average pore size of the porous polymer film is 0.1-0.22 μm. If the pore size is too small, it will bring too high transmission resistance, and if the pore size is too large, it will reduce the mechanical support force, thereby reducing the mechanical strength of the graphene oxide film.

[0012] A second aspect of the present invention is to provide a method for preparing a heterogeneous membrane with different functionalized channels, comprising the following steps:

[0013] (1) Amination of graphene oxide nanosheets:

[0014] The group activator 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) was dispersed in the graphene oxide dispersion and stirred until homogeneous. The amine-containing polymer was added to the stirred dispersion, stirred and dispersed again until homogeneous, and dialyzed to obtain an amination-modified graphene oxide nanosheet dispersion.

[0015] (2) Sulfonic acid grouping of graphene oxide nanosheets:

[0016] A polymer with sulfonic acid groups was added to a graphene oxide dispersion, and after sonication and stirring, a sulfonic acid-grouped graphene oxide nanosheet dispersion was obtained.

[0017] (3) Preparation of heterogeneous membranes with different functionalized channels:

[0018] A certain mass of amino-modified graphene oxide nanosheets and sulfonic acid-modified graphene oxide nanosheets were sequentially deposited onto a base film using a vacuum filtration method and then dried to obtain the heterogeneous film with different functionalized channels.

[0019] The present invention is further configured such that the graphene oxide dispersion described in steps (1) and (2) is prepared using a modified Hummers method. The modified Hummers method is as follows:

[0020] Potassium persulfate, phosphorus pentoxide, and concentrated sulfuric acid are mixed and heated to 78-82℃. Then, they are mixed with natural graphite, kept at the temperature, and cooled to room temperature. After dilution with deionized water, the mixture is allowed to stand for 12-18 hours, filtered, and dried to complete the pre-oxidation of graphite. The pre-oxidized material is mixed with concentrated sulfuric acid at 0-5℃, then reacted with potassium permanganate at 34-36℃ for 1.5-2.5 hours, and then reacted with hydrogen peroxide to obtain a mixture, thus completing the oxidation and exfoliation of graphite. The mixture is washed, filtered, and sonicated to obtain a graphene oxide dispersion.

[0021] The present invention is further configured such that the graphene oxide dispersion in steps (1) and (2) is a suspension of graphene oxide nanosheets with single-atom layers and an average layer size of about 5 μm (5 ± 1 μm).

[0022] The present invention further specifies that the concentration of the graphene oxide dispersion in steps (1) and (2) is 2-5 mg / mL. A low concentration of graphene oxide will reduce the membrane preparation efficiency, while an excessively high concentration will affect the dispersibility of the nanosheets in the dispersion, resulting in an uneven membrane.

[0023] The present invention is further configured such that the amine-containing polymer in step (1) is selected from one or more of polyethyleneimine (PEI), polyacrylamide (PAM), and polyallylamine (PAH), and the mass ratio of the amine-containing polymer to graphene oxide is (0.5-4):1, preferably (0.5-2):1, more preferably (1-2):1; and the ratio (μL / mg) of the amount of group activator EDC to graphene oxide added is (1-2):1.

[0024] The present invention is further configured such that the polymer with sulfonic acid groups in step (2) is selected from one or more of polystyrene sulfonic acid (PSS) and poly-2-acrylamide-2-methylpropanesulfonic acid (PAMPS), and the mass ratio of the polymer with sulfonic acid groups to graphene oxide is (0.2-1):1, preferably (0.2-0.8):1, more preferably (0.2-0.5):1.

[0025] The present invention further specifies that the stirring in steps (1) and (2) is preferably magnetic stirring, with a stirring speed of 600-1200 r / min and a stirring time of 3-5 h, preferably 4 h. Appropriate stirring is beneficial for the polymer to fully contact with the graphene oxide nanosheets, while excessive stirring will affect the structure and properties of the nanosheets.

[0026] The present invention further specifies that, in step (3), the deposition (mass) ratio of amino-modified graphene oxide nanosheets to sulfonic acid-modified graphene oxide nanosheets is (0.5-2):1, preferably 1:1; the deposition densities are 0.015-0.075 mg / cm³, respectively. 2 The preferred concentration is 0.030-0.045 mg / cm³. 2 More preferably, it is 0.038 mg / cm³. 2 .

[0027] The present invention is further configured such that the driving pressure of the vacuum filtration in step (3) is 0.1-0.5 MPa. Too low a pressure will cause the laminated membrane structure of the graphene oxide membrane to be loose and have low mechanical strength; while too high a pressure will cause the laminated membrane structure to be too tight, which is not conducive to ion transport.

[0028] The present invention is further configured such that the drying temperature in step (3) is 25-60℃ and the drying time is 12-36h. The drying process can remove moisture from the membrane, making the membrane structure more compact. If the drying temperature is too low, the membrane preparation efficiency will be reduced, while if the drying temperature is too high, the oxygen-containing functional groups on the surface of graphene oxide will be removed, damaging the membrane structure.

[0029] A third aspect of the invention is the application of the heterogeneous membrane with different functionalized channels for the extraction of lithium ions in a magnesium-lithium mixed system. Specifically, it is used for lithium extraction from salt lake brine. The heterogeneous membrane has a maximum magnesium-lithium selectivity of 31.0, while the lithium ion transport rate is 0.16 mol·m⁻¹. -2 h -1 .

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) This invention prepares heterogeneous films with different functionalized channels by modifying graphene oxide nanosheets with amination and sulfonic acid groups respectively, and then depositing them sequentially. Among them, the two-dimensional channels functionalized with sulfonic acid groups enhance the negative charge properties of the graphene oxide nanochannels, which facilitates the attraction of lithium ions into the channels through electrostatic attraction. At the same time, the sulfonic acid groups have a low binding energy for lithium ions, which is conducive to the rapid transport of lithium ions. The amination-modified two-dimensional channels activated by EDC not only provide positive charge properties, but also reduce the swelling effect of the film in aqueous solution through covalent and electrostatic interactions with the nanosheets, effectively controlling the interlayer spacing. Based on the charge difference between magnesium ions and lithium ions and the size difference of hydrated ions, the amination-modified two-dimensional channels with fixed interlayer spacing and positive charge properties can further hinder the passage of magnesium ions.

[0032] By adjusting the density of membrane groups, heterogeneous functionalized channels with lithium-ion transport layers and magnesium-lithium-ion separation layers can simultaneously exhibit high lithium-ion transport rates and magnesium-lithium selectivity.

[0033] (2) This invention modifies the two-dimensional channels of graphene oxide at the microscopic level, enabling microscopic control over the structure and performance of the channels. Furthermore, the microscopic control method makes the prepared membrane channels more regular and uniform, avoiding problems such as uneven membrane channel structure and properties in macroscopic control methods.

[0034] (3) The above preparation method is simple and easy to operate. The prepared membrane has high mechanical strength and stable structure. It can selectively transport lithium ions, but hinders the transport of other ions such as magnesium. It has high ion sieving performance and has good application prospects in lithium extraction from salt lake brine. Attached Figure Description

[0035] Figure 1 The image shows the zeta potential diagrams of the amino-modified graphene oxide dispersion and the sulfonic acid-modified graphene oxide dispersion prepared in Example 1.

[0036] Figure 2 These are (a) surface SEM and (b) cross-sectional SEM images of the heterostructure membrane prepared in Example 1.

[0037] Figure 3 These are the lithium / magnesium separation performance test results of heterogeneous membranes with different polystyrene sulfonic acid contents prepared in Examples 1-5;

[0038] Figure 4 The results show the lithium / magnesium separation performance of the graphene membranes prepared in Comparative Examples 1-3 and Example 1.

[0039] Figure 5 The results show the lithium / magnesium separation performance of the heterogeneous membranes prepared in Comparative Examples 4-6. Detailed Implementation

[0040] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. It should be understood that the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of the present invention.

[0041] Example 1

[0042] Graphene oxide dispersions were prepared using a modified Hummers method and diluted with deionized water to 2 mg / mL.

[0043] (1) Amination of graphene oxide nanosheets:

[0044] Take 50 mL of graphene oxide dispersion, add 200 μL of functional group activator EDC, and magnetically stir for 1 h at 1000 r / min at room temperature to ensure thorough mixing. Add 0.2 g of polyethyleneimine solution with a molecular weight of 10000 to the functional group-activated graphene oxide nanosheet dispersion, and continue stirring at the same speed for 4 h at room temperature. Transfer the thoroughly mixed and amination-modified dispersion to a dialysis bag with a molecular weight of 10000 and dialyze for 7 days to remove ungrafted polyethyleneimine molecular chains, obtaining a stable amination-modified graphene oxide dispersion.

[0045] The zeta potential of the amination-modified graphene oxide dispersion was tested, such as... Figure 1 As shown, under different pH conditions, the amination-modified GO dispersion exhibits positive charge compared to the original negatively charged graphene oxide (GO) dispersion, indicating that the amino groups have been successfully grafted onto the nanosheet surface.

[0046] (2) Sulfonic acid grouping of graphene oxide nanosheets:

[0047] Take 50 mL of graphene oxide dispersion, add polystyrene sulfonic acid, sonicate for 0.5 h, and magnetically stir at room temperature for 3 h. The amount of polystyrene sulfonic acid added is 50 mg, and the speed of the magnetic stirrer is 1000 r / min, to obtain a sulfonic acid-grouped graphene oxide dispersion.

[0048] The zeta potential of the sulfonated graphene oxide dispersion was tested, such as... Figure 1 As shown, the sulfonated graphene oxide suspensions exhibit electronegativity under different pH conditions. However, compared to the original graphene oxide dispersion, the electronegativity is increased, indicating that the polystyrene sulfonate molecular chains are bonded to the surface of the graphene oxide nanosheets.

[0049] (3) Preparation of heterogeneous membranes with different functionalized channels

[0050] Different functionalized graphene oxide dispersions were diluted 20-fold and dispersed under ultrasonic conditions of 700 W for 0.5 h. 5 mL of the amino-functionalized graphene oxide dispersion was taken and diluted again with deionized water to 50 mL. The dispersion was then deposited using vacuum filtration to a surface with an effective area of ​​13.41 cm². 2 The mixed cellulose ester microporous filter membrane was deposited on a 5 mL sulfonic acid-grouped graphene oxide dispersion, diluted to 50 mL with deionized water, and then deposited as a second layer on top of the amino-functionalized layer. The heterogeneous membrane obtained by vacuum filtration was dried in an oven at 60 °C for 12 h to obtain heterogeneous membranes with different specific functionalizations.

[0051] The morphology of the obtained heterostructure was observed, and its surface and cross-section SEM images are shown below. Figure 2 As shown, its surface exhibits an irregular distribution of wrinkles, a typical characteristic of two-dimensional graphene oxide films. The tortuous morphology shows a distinct layered structure, with a thickness exceeding 400 nm.

[0052] (4) Magnesium-lithium separation performance test of heterogeneous membrane

[0053] The target membrane was cut to a suitable size and sealed in a self-made U-shaped device. 80 mL of a mixed solution of LiCl and MgCl₂ (both with a concentration of 0.1 mol / L) was added to both sides, and the same volume of deionized water was added to the other side. The sulfonic acid functionalized layer faced the mixed ion solution. After 8 hours of free permeation, the solution from the deionized water side was collected, and the ion concentration was measured using ICP-OES. During the free permeation process, magnetic stirring was used on both sides to prevent ion concentration polarization. The calculated lithium ion permeation rate was 0.16 mol·m⁻¹. -2 h -1 The selectivity for lithium / magnesium ions was 31.0.

[0054] Example 2

[0055] The preparation method is the same as in Example 1, except that: there is no need to sulfonate the graphene oxide nanosheets. When preparing heterogeneous membranes with different functionalized channels, an amino-modified graphene oxide nanolayer is first deposited on a porous membrane substrate by vacuum filtration, followed by the sequential deposition of a layer of original graphene oxide nanolayer of the same mass.

[0056] In the magnesium / lithium separation performance test, the lithium ion permeation rate was 0.08 mol·m⁻¹. -2 h -1 The lithium / magnesium selectivity is 6.2.

[0057] Example 3

[0058] The preparation method is the same as in Example 1, except that the amount of polystyrene sulfonic acid added is 5 mg when preparing sulfonic acid-grouped graphene oxide nanosheets. That is, the mass ratio of the polymer with sulfonic acid groups to graphene oxide is 0.05:1.

[0059] In the lithium / magnesium separation test, the lithium ion permeation rate was 0.09 mol·m⁻¹. -2 h -1 The lithium / magnesium selectivity is 10.2.

[0060] Example 4

[0061] The preparation method is the same as in Example 1, except that the amount of polystyrene sulfonic acid added is 20 mg when preparing sulfonic acid-grouped graphene oxide nanosheets. That is, the mass ratio of the polymer with sulfonic acid groups to graphene oxide is 0.2:1.

[0062] In the lithium / magnesium separation test, the lithium ion permeation rate was 0.14 mol·m⁻¹. -2 h -1 The lithium / magnesium selectivity is 23.2.

[0063] Example 5

[0064] The preparation method is the same as in Example 1, except that the amount of polystyrene sulfonic acid added is 80 mg when preparing sulfonic acid-grouped graphene oxide nanosheets. That is, the mass ratio of the polymer with sulfonic acid groups to graphene oxide is 0.8:1.

[0065] In the lithium / magnesium separation test, the lithium ion permeation rate was 0.24 mol·m⁻¹. -2 h -1 The lithium / magnesium selectivity was 14.9.

[0066] like Figure 3As shown, the separation performance of heterogeneous membranes with different polystyrene sulfonic acid contents prepared in Examples 1-5 in the magnesium-lithium separation test is shown. When the mass ratio of polymer with sulfonic acid groups to graphene oxide is (0.2-0.8):1, the lithium / magnesium separation effect is significant.

[0067] Example 6 Simulated brine magnesium / lithium separation performance test

[0068] The preparation methods for amino- and sulfonic acid-based graphene oxide nanosheets are the same as in Example 1. The difference is that, in preparing the heterostructure, the deposition amounts of amino-based and sulfonic acid-based graphene oxide nanosheets are 1.25 mg each, resulting in a heterostructure with a total graphene oxide thickness of approximately 1 μm.

[0069] Reverse osmosis separation experiments were conducted using a simulated brine mixture with a high magnesium / lithium ratio (magnesium concentration of 1866 mg / L, lithium concentration of 134 mg / L, magnesium / lithium ratio of approximately 13.9). Under a pressure of 0.1 MPa, the lithium permeation rate was 1.03 mol·m⁻¹. -2 h -1 The lithium / magnesium selectivity was 9.1. Compared to the forward osmosis system, although the lithium / magnesium selectivity decreased, the lithium transport rate was significantly improved due to pressure drive, resulting in excellent overall performance.

[0070] Comparative Example 1: Lithium / Magnesium Separation Performance Test of Unmodified Graphene Oxide Membrane

[0071] (1) Preparation of graphene oxide dispersion

[0072] A graphene oxide dispersion was prepared by a modified Hummers method and diluted with deionized water to 0.1 mg / mL. 10 mL of this dispersion was further diluted to 50 mL and sonicated at 700 W for 30 min to obtain a uniform graphene oxide dispersion.

[0073] (2) Preparation of graphene oxide (GO) film

[0074] A graphene oxide dispersion was deposited onto a mixed cellulose ester substrate with a pore size of 0.22 μm via vacuum filtration. The membrane with substrate support was then placed in an oven at 60 °C and dried for 12 h to obtain a graphene oxide membrane with substrate support.

[0075] (3) Testing of magnesium / lithium separation performance of graphene oxide membrane

[0076] The lithium / magnesium separation performance was tested using the same method as in Example 1. Analysis showed that the lithium ion permeation rate was 0.19 mol·m⁻¹. -2 h -1 The selectivity for lithium / magnesium ions is 1.7.

[0077] Comparative Example 2: Lithium / Magnesium Separation Performance Test of Sulfonic Acid-Grouped Graphene Oxide Membrane

[0078] (1) Preparation of sulfonated graphene oxide nanosheets

[0079] The preparation method of sulfonate-grouped graphene oxide nanosheets is the same as in Example 1.

[0080] (2) Preparation of sulfonated graphene oxide (GO-PSS) film

[0081] The sulfonic acid-grouped nanosheet dispersion was diluted 20-fold, and 10 mL was diluted with deionized water to 50 mL. The solution was then sonicated at 700 W for 30 min. The nanosheets were then deposited onto a mixed cellulose ester substrate via vacuum filtration. The substrate-supported membrane was placed in a 60 °C oven and dried for 12 h to obtain a substrate-supported sulfonic acid-grouped graphene oxide membrane.

[0082] (3) Testing of magnesium / lithium separation performance of sulfonated graphene oxide membrane

[0083] The lithium / magnesium separation performance was tested using the same method as in Example 1. Analysis showed that the lithium ion permeation rate was 0.34 mol·m⁻¹. -2 h -1 The selectivity for lithium / magnesium ions is 8.3.

[0084] Comparative Example: Lithium / Magnesium Separation Performance Testing of 3 Aminolated Graphene Oxide Membranes

[0085] (1) Preparation of amino-modified graphene oxide nanosheets

[0086] The preparation method of amino-modified graphene oxide nanosheets is the same as in Example 1.

[0087] (2) Preparation of amino-modified graphene oxide (GO-PEI) film

[0088] The amination of nanosheets was diluted 20-fold, and 10 mL was diluted with deionized water to 50 mL. The solution was then sonicated at 700 W for 30 min. The nanosheets were then deposited onto a mixed cellulose ester substrate by vacuum filtration. The substrate-supported membrane was placed in a 60 °C oven and dried for 12 h to obtain a substrate-supported amination of graphene oxide membrane.

[0089] (3) Testing of magnesium / lithium separation performance of amination-modified graphene oxide membrane

[0090] The lithium / magnesium separation performance was tested using the same method as in Example 1. Analysis showed that the lithium ion permeation rate was 0.06 mol·m⁻¹. -2 h -1 The selectivity for lithium / magnesium ions is 10.4.

[0091] Comparative Examples 1-3 show graphene films prepared from unmodified graphene oxide and graphene films prepared only by sulfonic acid grouping and amination modification, respectively. The lithium / magnesium separation performance test results are as follows: Figure 4 As shown, the lithium / magnesium separation performance is significantly reduced compared to Example 1.

[0092] Comparative Example 4: Lithium / Magnesium Separation Performance Test of Sodium Alginate Modified Heterogeneous Membrane

[0093] (1) Preparation of amino-modified graphene oxide nanosheets

[0094] The preparation method of amino-modified graphene oxide nanosheets is the same as in Example 1.

[0095] (2) Preparation of sodium alginate-modified negatively charged nanosheets

[0096] Take 50 mL of graphene oxide dispersion, add sodium alginate solution, sonicate for 0.5 h, and magnetically stir at room temperature for 3 h. The amount of sodium alginate added is 50 mg, and the speed of the magnetic stirrer is 1000 r / min, to obtain a sodium alginate-modified graphene oxide dispersion.

[0097] (3) Preparation of sodium alginate-modified heterogeneous membrane (SA-jGO)

[0098] The preparation method is the same as in Example 1, except that the sulfonic acid grouped graphene oxide dispersion is replaced with a sodium alginate modified graphene oxide dispersion.

[0099] (4) Testing of magnesium / lithium separation performance of sodium alginate-modified heterogeneous membrane

[0100] The lithium / magnesium separation performance was tested using the same method as in Example 1. Analysis showed that the lithium ion permeation rate was 0.11 mol·m⁻¹. -2 h -1 The selectivity for lithium / magnesium ions is 15.3.

[0101] Comparative Example 5: Lithium / Magnesium Separation Performance Test of Polyacrylic Acid Modified Heterogeneous Membrane

[0102] (1) Preparation of amino-modified graphene oxide nanosheets

[0103] The preparation method of amino-modified graphene oxide nanosheets is the same as in Example 1.

[0104] (2) Preparation of polyacrylic acid modified negatively charged nanosheets

[0105] Take 50 mL of graphene oxide dispersion, add polyacrylic acid solution, sonicate for 0.5 h, and magnetically stir at room temperature for 3 h. The amount of polyacrylic acid added is 50 mg, and the speed of the magnetic stirrer is 1000 r / min, to obtain polyacrylic acid modified graphene oxide dispersion.

[0106] (3) Preparation of polyacrylic acid modified heterostructure (PAA-jGO)

[0107] The preparation method is the same as in Example 1, except that the sulfonic acid-modified graphene oxide dispersion is replaced with a polyacrylic acid-modified graphene oxide dispersion.

[0108] (4) Testing of lithium / magnesium separation performance of polyacrylic acid modified heterogeneous membrane

[0109] The lithium / magnesium separation performance was tested using the same method as in Example 1. Analysis showed that the lithium ion permeation rate was 0.09 mol·m⁻¹. -2 h -1 The selectivity for lithium / magnesium ions is 12.7.

[0110] As shown in Comparative Examples 4-5, although the prepared membranes also possess positive / negative charge heterostructures, the difference in the negative charge modification groups significantly reduces the lithium permeation rate and lithium / magnesium selectivity. This demonstrates that sulfonic acid groups play an irreplaceable role in lithium / magnesium separation.

[0111] Test of lithium / magnesium separation performance of the reverse heterostructure membrane in Comparative Example 6

[0112] The preparation of functionalized graphene oxide nanosheets was the same as in Example 1. The difference was that, during the preparation of the heterostructure, sulfonic acid-functionalized graphene oxide and amino-functionalized graphene oxide were deposited sequentially. In the lithium / magnesium ion separation performance test, the amino-functionalized channels faced the mixed ion side. Analysis showed that the lithium ion permeation rate was 0.07 mol·m⁻¹. -2 h -1 The selectivity for lithium / magnesium ions is 26.0.

[0113] The double-sided graphene oxide membrane in the heterogeneous membrane with different functionalized channels described in this invention has directionality. When the membrane is reversed, the lithium ion permeation rate decreases significantly, which is not conducive to lithium transport and lithium / magnesium separation.

[0114] The lithium / magnesium separation performance test results of the heterostructures prepared in Comparative Examples 4-6 are as follows: Figure 5 As shown, compared with Example 1, changing the modified groups and changing the deposition order both resulted in a significant decrease in lithium / magnesium separation performance.

[0115] This application provides a detailed description, the purpose of which is to enable those skilled in the art to understand and implement the content of this application, but it should not be used to limit the scope of protection of this application. All equivalent changes or modifications made in accordance with the spirit and essence of this application should be covered within the scope of protection of this application.

Claims

1. A heterogeneous membrane with different functionalized channels, characterized in that, The heterogeneous film comprises a base film and a double-sided graphene oxide film deposited on one side of the base film. The double-sided graphene oxide film comprises sequentially deposited graphene oxide nanosheets modified with amino groups and graphene oxide nanosheets modified with sulfonic acid groups, wherein: The amine functionalization modification uses a polymer with amine groups, wherein the polymer with amine groups is selected from one or more of polyethyleneimine, polyacrylamide, and polyallylamine; The sulfonic acid functionalization modification uses a polymer with sulfonic acid groups, wherein the polymer with sulfonic acid groups is selected from one or more of polystyrene sulfonic acid and poly2-acrylamide-2-methylpropanesulfonic acid.

2. The heterogeneous membrane with different functionalized channels according to claim 1, characterized in that, The thickness of the double-sided graphene oxide film is 200-1000 nm.

3. The heterogeneous membrane with different functionalized channels according to claim 2, characterized in that, The thickness of the double-sided graphene oxide film is 400-600 nm.

4. The heterogeneous membrane with different functionalized channels according to claim 1, characterized in that, The base membrane is a porous polymer membrane, and the material is selected from one of mixed cellulose ester, nylon, polyacrylonitrile, and polycarbonate; the average pore size of the porous polymer membrane is 0.1-0.22µm.

5. A method for preparing a heterogeneous membrane with different functionalized channels, characterized in that, Includes the following steps: (1) Disperse the group activator 1-ethyl-(3-dimethylaminopropyl)carbodiimide into the graphene oxide dispersion and stir until uniform; add the polymer with amine groups, stir until uniform, and dialyze to obtain an amination-modified graphene oxide nanosheet dispersion. (2) Add the polymer with sulfonic acid groups to the graphene oxide dispersion, sonicate and continue stirring to obtain a sulfonic acid grouped graphene oxide nanosheet dispersion. (3) Amine-modified graphene oxide nanosheets and sulfonic acid-modified graphene oxide nanosheets are sequentially deposited onto the base film by vacuum filtration and dried to obtain the heterogeneous film with different functionalized channels. The polymer with amine groups is selected from one or more of polyethyleneimine, polyacrylamide, and polyallylamine, and the polymer with sulfonic acid groups is selected from one or more of polystyrene sulfonic acid and poly2-acrylamide-2-methylpropanesulfonic acid.

6. The method for preparing heterogeneous membranes with different functionalized channels according to claim 5, characterized in that, The graphene oxide dispersions described in steps (1) and (2) are suspensions of graphene oxide nanosheets with single-atom layers and an average layer size of 5±1μm, prepared using a modified Hummers method.

7. The method for preparing heterogeneous membranes with different functionalized channels according to claim 5, characterized in that, The concentration of the graphene oxide dispersion described in steps (1) and (2) is 2-5 mg / mL.

8. The method for preparing heterogeneous membranes with different functionalized channels according to claim 5, characterized in that, In step (1), the mass ratio of the amine-containing polymer to graphene oxide is (0.5-4):1; the ratio of the amount of group activator to graphene oxide added (µL / mg) is (1-2):

1.

9. The method for preparing a heterogeneous membrane with different functionalized channels according to claim 8, characterized in that, The mass ratio of the amine-containing polymer to graphene oxide is (0.5-2):

1.

10. The method for preparing a heterogeneous membrane with different functionalized channels according to claim 5, characterized in that, The mass ratio of the polymer with sulfonic acid groups to graphene oxide in step (2) is (0.2-1):

1.

11. The method for preparing a heterogeneous membrane with different functionalized channels according to claim 10, characterized in that, The mass ratio of the polymer with sulfonic acid groups to graphene oxide is (0.2-0.8):

1.

12. The method for preparing a heterogeneous membrane with different functionalized channels according to claim 11, characterized in that, The mass ratio of the polymer with sulfonic acid groups to graphene oxide is (0.2-0.5):

1.

13. The method for preparing a heterogeneous membrane with different functionalized channels according to claim 5, characterized in that, In step (3), the deposition mass ratio of the amino-modified graphene oxide nanosheets to the sulfonic acid-modified graphene oxide nanosheets is (0.5-2):1; the deposition density is 0.015-0.075 mg / cm³. 2 .

14. The method for preparing a heterogeneous membrane with different functionalized channels according to claim 13, characterized in that, In step (3), the deposition mass ratio of the amino-modified graphene oxide nanosheets to the sulfonic acid-modified graphene oxide nanosheets is 1:1, and the deposition density is 0.030-0.045 mg / cm³. 2 .

15. The application of the heterogeneous membrane with different functionalized channels as described in any one of claims 1-4, characterized in that, Used for lithium-magnesium separation in mixed systems of lithium and magnesium ions.

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