Mxene / polyazole flexible composite hydrogel and preparation method and application thereof

Abstract

The application belongs to the technical field of functional hydrogel and its adsorption and extraction application, and provides Mxene / polyazole flexible composite hydrogel, a preparation method and application thereof, so as to solve the problem of poor flexibility and mechanical property of the current hydrogel. The hydrogel is MXene / PPy / HMO composite flexible hydrogel, and is directly used as a bulk material to realize lithium recovery. Lithium ion sieve (HMO), MXene and polyazole network are crosslinked with each other to form a three-dimensional network structure; the mass of MXene is 1%-5% of the polyazole hydrogel, a Mxene network is formed through physical crosslinking, the contained elements are carbon and titanium, and the atomic number ratio is 2:3; a polyazole hydrogel network is formed through chemical crosslinking. In the presence of MXene and HMO, polyvinyl alcohol and sodium dodecyl sulfonate are introduced, and in-situ polymerization can be carried out. The hydrogel has good flexibility and stretchability, and can be self-healing. The method is simple and easy to implement, and a flexible liquid lithium adsorbent can be directly prepared.

Description

Technical Field

[0001] This invention belongs to the technical field of functional hydrogels and their adsorption and extraction applications, specifically relating to an Mxene / polypyrrole flexible composite hydrogel, its preparation method and application. The hydrogel is an MXene / PPy / HMO composite flexible hydrogel, which is used for lithium extraction from seawater. Background Technology

[0002] Although manganese-based lithium ion sieves are effective against Li + While exhibiting excellent selectivity, its application in physical lithium extraction still faces several challenges: significant Mn dissolution during acid leaching; easy powder loss during adsorption; and prolonged adsorption time. Solutions to these problems include: controlling morphology and structure or doping with metal elements to hinder Mn dissolution during acid leaching; and introducing binders to immobilize λ-MnO2 to facilitate solid-liquid separation.

[0003] Commonly used binders include polymers such as polyacrylamide (PAM), polyacrylonitrile (PAN), and polyvinyl chloride (PVC), which can enable materials to be granulated, membrane-formed, fibrous, or magnetized. However, the introduction of binders and the like blocks the active sites of the encapsulated lithium ion sieve (HMO) particles, affecting both the mass transfer rate and the adsorption capacity. Introducing ion sieves into polymers to prepare membrane adsorbents can overcome the drawback of powdered adsorbents being easily dissolved and destroyed.

[0004] In recent years, scientists have prepared hybrid matrix nanofiber membranes containing dispersed lithium-ion sieves (LIS) via electrospinning, exhibiting high specific surface area and porosity. However, the high specific surface area design leads to a decrease in the mechanical strength of the membrane, causing it to break during adsorption. Furthermore, cost and recyclability also limit its application.

[0005] Hydrogels comprise an interesting class of viscoelastic materials composed of a three-dimensional (3D) network of hydrophilic polymers cross-linked through chemical or physical means, possessing the ability to absorb and retain large amounts of water. In recent years, scientists have proposed constructing 3D porous polypyrrole hydrogels to effectively improve processability.

[0006] MXene is a novel 2D material. MXene prepared by selective etching contains multiple functional groups (F-, O-, and OH-) on its surface and edges. - Therefore, it has good dispersibility in water, and when combined with polypyrrole hydrogel, it can exhibit extremely high tensile strength and self-healing properties. Summary of the Invention

[0007] To address the current issues of poor flexibility and mechanical properties of hydrogels, this invention provides an MXene / polypyrrole flexible composite hydrogel, its preparation method, and its application. This hydrogel is an MXene / PPy / HMO composite flexible hydrogel that can be directly used as a bulk material for lithium recovery.

[0008] The present invention is achieved by the following technical solution: a flexible Mxene / polypyrrole composite hydrogel, wherein the Mxene / polypyrrole flexible composite hydrogel is formed by cross-linking HMO, MXene and polypyrrole network to form a three-dimensional network structure; wherein: the mass of MXene is 1%-5% of the mass of polypyrrole hydrogel, the physical cross-linking forms the Mxene network, the contained elements are carbon and titanium, and the atomic ratio is 2:3; the chemical cross-linking forms the polypyrrole hydrogel network.

[0009] The method for preparing the Mxene / polypyrrole flexible composite hydrogel involves in-situ polymerization of polyvinyl alcohol and sodium dodecyl sulfonate in the presence of MXene and HMO. The specific method is as follows:

[0010] (1) Dissolve polyvinyl alcohol (PVA) in deionized water and heat at 60°C and 90°C for 1 hour respectively to obtain a transparent PVA solution, wherein the mass of PVA is 10% of the mass of the solvent;

[0011] (2) Mix 1.5-4.5 g of the transparent PVA solution obtained in step (1) with 115-460 mg of sodium dodecyl sulfonate SDS until homogeneous; dissolve 0.5-2 g of MXene in 0.5-2 mL of deionized water, and after ultrasonic dispersion, inject the MXene solution into the mixed solution of PVA and SDS using a pipette. Stir at 50°C until no more bubbles appear. Add 70-280 µl of pyrrole Py to the mixed solution and continue stirring until completely homogeneous. Label this solution as solution A.

[0012] (3) Dissolve 228-912 mg of strong oxidant ammonium persulfate (APS) in 430-1720 µl of deionized water, then add a certain amount of HMO and stir until homogeneous. This solution is labeled as solution B, where the mass ratio of HMO is 5%-65% of the total mass of solution B.

[0013] (4) Place solution A and solution B at 4°C for 10 minutes, then quickly inject solution B into solution A and place for 12 hours to obtain MXene / PPy / HMO flexible composite hydrogel.

[0014] (5) The prepared composite hydrogel was soaked in 0.5M sulfuric acid for 6 hours, rinsed with deionized water and placed in a sealed bag for later use.

[0015] The present invention also provides the application of the aforementioned Mxene / polypyrrole flexible composite hydrogel in lithium extraction from seawater.

[0016] The Mxene / polypyrrole flexible composite hydrogel prepared by this invention has a three-dimensional network structure and exhibits good flexibility and stretchability. This method is simple and easy to implement, and can directly prepare flexible liquid lithium adsorbents. Attached Figure Description

[0017] Figure 1 Transmission electron microscope (TEM) images of MXene at different magnifications; A, B, and C in the figure are MXene images at different magnifications.

[0018] Figure 2 The image shows a TEM image of polypyrrole (PPy) hydrogel; A and B in the image are transmission electron microscope images of the polypyrrole hydrogel at different magnifications.

[0019] Figure 3 The image shows a flexible composite hydrogel of MXene / PPy / HMO; A, B, and C in the figure are transmission electron microscope images of the polypyrrole hydrogel at different magnifications.

[0020] Figure 4 The images show actual photos of the MXene / PPy / HMO composite hydrogel and its self-healing mechanism. In the images: A shows the flexibility of the MXene / PPy / HMO composite hydrogel, and B shows its self-healing mechanism.

[0021] Figure 5 The image shows the actual tensile test specimen of the MXene / PPy / HMO composite hydrogel; in the figure: A is a picture of the MXene / PPy / HMO composite hydrogel placed on glass after preparation; B and C are tensile test specimens.

[0022] Figure 6 To simulate the cyclicity of lithium extraction from seawater using MXene / PPy / HMO composite hydrogels;

[0023] Figure 7 Artificial seawater selectivity for MXene / PPy / HMO composite hydrogels;

[0024] Figure 8 Mechanical properties of the MXene / PPy / HMO composite hydrogel before and after 6 cycles of continuous use. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but 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 protection of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and all materials publicly cited herein and cited by them are incorporated herein by reference.

[0027] Equivalent technologies of the specific embodiments described herein that are readily apparent to those skilled in the art through routine experimentation are included in this application.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the instruments and equipment used in the following examples are all standard laboratory instruments and equipment; unless otherwise specified, the experimental materials used in the following examples were all purchased from regular biochemical reagent stores.

[0029] Example 1: Polyvinyl alcohol (PVA) was dissolved in deionized water and heated at 60°C and 90°C for 1 hour to obtain a transparent PVA solution, wherein the mass of PVA was 10% of the mass of water. 1.5 g of PVA solution and 115 mg of SDS were mixed evenly. 0.5 g of MXene was dissolved in 0.5 mL of deionized water and ultrasonically dispersed. The mixture was then injected into the above mixed solution using a pipette and stirred at 50°C until no more bubbles appeared. 70 μL of pyrrole was added to the mixed solution and stirred until completely homogeneous. This solution was labeled as solution A. 228 mg of ammonium persulfate (APS) was dissolved in 430 μL of deionized water and 20 mg of HMO was added. This solution was labeled as solution B. Solutions A and B were placed at 4°C for 10 minutes. Solution B was then rapidly injected into solution A and left to stand for 12 hours to obtain a flexible composite hydrogel of MXene / PPy / HMO. The prepared composite hydrogel was soaked in 0.5M sulfuric acid for 6 hours, rinsed with deionized water, and then placed in a sealed bag for later use.

[0030] Figure 1 The image shows a TEM image of MXene, which reveals a two-dimensional sheet-like structure. Figure 2 The image shows a TEM image of a single PPy hydrogel, which reveals a macroporous structure. Figure 3 The image shows a TEM image of the MXene / PPy / HMO composite hydrogel. The introduction of MXene did not disrupt the structure of the PPy hydrogel, and MXene was uniformly composited with the polypyrrole hydrogel. Figure 4 The image shows a physical picture of the MXen / PPy / HMO composite hydrogel. The image shows that the hydrogel exhibits good flexibility and can heal. Figure 5 This is a schematic diagram of stretching the prepared hydrogel, showing that the hydrogel exhibits good stretchability. Figure 6The results of lithium extraction from the composite hydrogel after five consecutive cycles show that the adsorption capacity was 19.8 mg / g (HMO). After continuous elution and five cycles, the adsorption capacity remained at 17.8 mg / g, maintaining 89.8%.

[0031] Example 2: 1 g MXene was dissolved in 0.5 mL of deionized water, and 30 mg HMO was added uniformly. Other methods were the same as described in Example 1. This change does not affect the toughness of the hydrogel. Since HMO is a key material for lithium adsorption, it is evident that the introduced HMO can be optimized.

[0032] Example 3: Add 140 μL of pyrrole to the mixed solution, dissolve 228 mg of ammonium persulfate (APS) in 370 μL of deionized water, add 40 mg of HMO evenly, and follow the same procedure as in Example 1.

[0033] Example 4: This invention also investigated the application of MXen / PPy / HMO composite hydrogels in simulated artificial seawater (0.17 mg / L). -1 Li + 10554 mg L -1 Na + 403.5 mg L -1 Ca 2+ 391 mg L -1 K + 1267.5 mg L -1 Mg 2+ The adsorption selectivity in ) is shown in the results as follows Figure 7 As shown, different ions exhibit different adsorption efficiencies; Li₂ was extracted from artificial seawater using the MXen / PPy / HMO composite hydrogel. + The efficiency was 96.1%, significantly higher than other ions (Na+). + Ca 2+ K + Mg 2+ The maximum extraction efficiency is <4%. This is because Li + The radius is smaller than Na + K + and Ca 2+ The radius of the Li, while the recognition sites in the MXen / PPy / HMO composite hydrogel, provided by HMO, only allow vacancies with radii less than or equal to Li. + The ions enter. However, Mg 2+ and Li + Although their radii are similar, their separation efficiency is still very low because Mg 2+ Hydration energy (−455 kcal mol) -1 Higher than Li+ (−122 kcal mol -1 ).

[0034] Therefore, the composite hydrogel prepared by this invention not only solves the problem of adsorption capacity, but also the problem of powder being difficult to recycle. Figure 8 It can be seen that even though the elongation of the nanocomposite hydrogel decreases slightly after 5 adsorption-desorption cycles, the composite hydrogel still has good flexibility.

[0035] MXene materials also reduce the interception effect of divalent metal ions and potassium ions with large ionic radii by other ions and Li. + Competition between them, thus promoting Li + Diffusion in composite materials. Therefore, using composite hydrogel-confined lithium-ion sieves is an effective strategy to solve the problems of difficult recovery and low adsorption capacity and rate in the seawater lithium extraction process using lithium-ion sieves.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A flexible Mxene / polypyrrole composite hydrogel, characterized in that: The Mxene / polypyrrole flexible composite hydrogel is a three-dimensional network structure formed by the cross-linking of lithium ion sieves (HMO), MXene, and polypyrrole networks. It can be polymerized in situ by introducing polyvinyl alcohol and sodium dodecyl sulfonate in the presence of MXene and HMO. Among them, MXene accounts for 1%-5% of the mass of polypyrrole hydrogel, and physical cross-linking forms an Mxene network. The elements contained are carbon and titanium, with an atomic ratio of 2:3; chemical cross-linking forms a polypyrrole hydrogel network.

2. The method for preparing the Mxene / polypyrrole flexible composite hydrogel according to claim 1, characterized in that: In the presence of MXene and HMO, in-situ polymerization can be achieved by introducing polyvinyl alcohol and sodium dodecyl sulfonate. The specific method is as follows: (1) Dissolve polyvinyl alcohol (PVA) in deionized water and heat at 60°C and 90°C for 1 hour respectively to obtain a transparent PVA solution, wherein the mass of PVA is 10% of the mass of the solvent; (2) Mix 1.5-4.5 g of the transparent PVA solution obtained in step (1) with 115-460 mg of sodium dodecyl sulfonate SDS until homogeneous; dissolve 0.5-2 g of MXene in 0.5-2 mL of deionized water, and after ultrasonic dispersion, inject the MXene solution into the mixed solution of PVA and SDS using a pipette. Stir at 50°C until no more bubbles appear. Add 70-280 µl of pyrrole Py to the mixed solution and continue stirring until completely homogeneous. Label this solution as solution A. (3) Dissolve 228-912 mg of strong oxidant ammonium persulfate (APS) in 430-1720 µl of deionized water, then add a certain amount of HMO and stir until homogeneous. This solution is labeled as solution B, where the mass ratio of HMO is 5%-65% of the total mass of solution B. (4) Place solution A and solution B at 4°C for 10 minutes, then quickly inject solution B into solution A and place for 12 hours to obtain MXene / PPy / HMO flexible composite hydrogel. (5) The prepared composite hydrogel was soaked in 0.5M sulfuric acid for 6 hours, rinsed with deionized water and placed in a sealed bag for later use.

3. The application of the Mxene / polypyrrole flexible composite hydrogel according to claim 1 or the Mxene / polypyrrole flexible composite hydrogel prepared by the method according to claim 2 in lithium extraction from seawater.

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