Preparation method and application of polyvinylidene fluoride polymer hydrogel adsorbent

Abstract

The application discloses a preparation method and application of a polyvinylidene fluoride (PVDF) polymer hydrogel adsorbent. The method comprises the following steps: (1) modifying PVDF powder by a KOH / ethanol solution to obtain active groups containing double bonds; (2) grafting polyacrylic acid (PAA) by free radical polymerization to form a PVDF-g-PAA amphiphilic polymer; and (3) cross-linking with acrylamide (AM) to construct a three-dimensional interpenetrating network hydrogel. An efficient lithium ion adsorbent can be obtained through only three simple steps, and the raw material is low in price and suitable for large-scale preparation. The adsorbent realizes efficient lithium adsorption, and the lithium ion adsorption capacity of the adsorbent in a salt lake brine alkaline environment reaches 33.48 mg / g, and the lithium-magnesium selectivity coefficient reaches 45. Experiments show that the adsorption capacity of the adsorbent still reaches 82% after several cycles, the adsorbent has excellent mechanical stability and cyclic regeneration capacity, and is particularly suitable for lithium resource extraction of high magnesium-lithium ratio salt lake brine.

Description

Technical Field

[0001] This invention belongs to the field of lithium adsorption material preparation technology, specifically relating to a preparation method and application of a polyvinylidene fluoride-containing polymer hydrogel adsorbent. Background Technology

[0002] As the global energy structure shifts towards cleaner energy sources, lithium resources, as a core material for high-energy-density batteries, are increasingly demonstrating their strategic importance. Salt lake brines, as a significant carrier of lithium resources, account for over 60% of global lithium reserves; however, their complex ionic composition (such as high concentrations of Na+) presents challenges. + K + Mg 2+ The low lithium concentration (typically 0.01-0.15%) makes efficient and selective lithium extraction a technological bottleneck. Traditional adsorption materials (such as manganese-based and titanium-based oxides) have certain adsorption capacity, but they generally suffer from poor selectivity, insufficient cycle stability, and easy agglomeration of nanoparticles, making it difficult to meet industrial needs.

[0003] Currently, the main technologies for lithium recovery both domestically and internationally include chemical precipitation, liquid-phase extraction, electrochemical reduction, membrane separation, and adsorption. Among these, adsorption is widely used for separating different ions in liquids due to its simplicity, environmental friendliness, and cost-effectiveness. In the lithium extraction process, lithium is selectively adsorbed and then desorbed from the solution, thus separating from coexisting ions. Several types of inorganic metal-based adsorbents (lithium aluminum layered double hydroxide (LiAl-LDH), lithium titanium oxide lithium-ion sieves (LTO-LIS), and lithium manganese oxide lithium-ion sieves (LMO-LIS)), metal-organic frameworks (MOFs), and crown ether-based adsorbents have been tested and reported for lithium recovery.

[0004] For example, Chinese invention patent document CN115475607B discloses a method for preparing a cationic amphiphilic fluorinated hydrogel adsorbent. The method involves solvents such as 1-vinylimidazolium, adding 1,6-dibromohexane, reacting to obtain an intermediate product, then reacting it with perfluoroalkyl acid. The product is filtered and purified by column chromatography to obtain a cationic amphiphilic fluorinated monomer. This amphiphilic fluorinated monomer is then reacted with acrylic acid monomer and N,N′-methylenebisacrylamide to finally obtain the fluorinated hydrogel adsorbent. However, this method is cumbersome in its preparation process, requiring column chromatography to treat the intermediate product, which is not conducive to large-scale production. Furthermore, perfluoroalkyl acid is expensive, resulting in a high overall cost for the adsorbent. Summary of the Invention

[0005] The purpose of this invention is to provide a simple and convenient technology that meets practical needs and addresses the problems of complex and costly existing lithium adsorbent synthesis processes. This invention provides a method for preparing a polyvinylidene fluoride (PVDF)-containing hydrogel adsorbent. This adsorbent utilizes the CF bonds of PVDF to bind with Li... + This material achieves highly efficient lithium adsorption through specific coordination and the ionization of the carboxylic acid group of PAA. The adsorption capacity of lithium ions in water can reach 33.48 mg / g at room temperature. The adsorption of other metal cations is relatively low. For example, the lithium-magnesium selectivity coefficient for magnesium ions can reach 45. It has good adsorption performance in alkaline environments, making it very suitable for the alkaline environment of salt lake brine. It can also be reused, which shows good sustainability and makes it have significant application potential.

[0006] To solve the technical problem of this invention, the proposed solution is as follows: A method for preparing a polyvinylidene fluoride-containing polymer hydrogel adsorbent, comprising the following steps:

[0007] (1) Preparation of modified polyvinylidene fluoride (PVDF) powder

[0008] a. First, prepare a 5-20% KOH aqueous solution by mass, then mix it with anhydrous ethanol at a volume ratio of 1:0.5-3. Disperse polyvinylidene fluoride powder evenly in the above KOH / anhydrous ethanol mixture, stir magnetically to ensure thorough dispersion, and then stir at 40-70 °C to obtain a brown solution;

[0009] b. The post-processing of the reaction solution includes the following steps: centrifugation to obtain the lower layer of solid, washing with deionized water, ultrasonic dispersion, centrifugation again, and repeating this step until the solution is washed to neutral. The obtained solid is freeze-dried under vacuum to obtain modified PVDF powder.

[0010] (2) Preparation of PVDF-g-PAA

[0011] a. Add the modified PVDF powder to a water / anhydrous ethanol (water to anhydrous ethanol volume ratio of 1:0.5-3), disperse it evenly by ultrasonication, then add azobisisobutyronitrile and acrylic acid monomer, and carry out free radical polymerization at 60-80 °C under nitrogen atmosphere.

[0012] b. Dilute the reaction solution with deionized water, then centrifuge it, and repeatedly wash and centrifuge it with deionized water to remove unreacted acrylic monomers. Finally, freeze-dry the obtained brown solid under vacuum to obtain dry PVDF-g-PAA powder.

[0013] (3) Preparation of PVDF-g-PAA / PAM polymer hydrogel adsorbent

[0014] a. First, ultrasonically disperse and mix PVDF-g-PAA with ultrapure water until uniform, then add N,N′-methylenebisacrylamide, ammonium persulfate, and acrylamide. After the drug is completely dissolved, react at 50-70 °C under a nitrogen atmosphere.

[0015] b. After the reaction is complete, wash the surface of the PVDF-g-PAA / PAM polymer hydrogel adsorbent with deionized water.

[0016] Preferably, in step (1)a, the mass fraction of KOH aqueous solution is 10%; the volume ratio of KOH aqueous solution to anhydrous ethanol in step (1)a is 1:1; the reaction temperature in step (1)a is 60 °C; the volume ratio of water to anhydrous ethanol in step (2)a is 1:1; the reaction temperature in step (2)a is 70 °C; in step (3)a, PVDF-g-PAA is 1000 mg, ultrapure water is 5 mL, N,N′-methylenebisacrylamide is 15 mg, ammonium persulfate is 15 mg, and acrylamide is 1000 mg; the reaction temperature in step (3)a is 60 °C.

[0017] Includes the following steps:

[0018] (1) Preparation of modified polyvinylidene fluoride (PVDF) powder

[0019] a. First, prepare 20 mL of 10% KOH aqueous solution, then mix it with 20 mL of anhydrous ethanol at a volume ratio of 1:1. Disperse 10 g of polyvinylidene fluoride powder evenly in the above KOH / anhydrous ethanol mixed solution, stir magnetically to ensure full dispersion, and then stir at 60 °C for 10 min to obtain a brown solution.

[0020] b. The post-processing of the reaction solution includes the following steps: centrifugation to obtain the lower layer solid, washing with deionized water, ultrasonic dispersion, centrifugation again, repeating this step until the solution is washed to neutral, and freeze-drying the obtained solid under vacuum for 24 hours to obtain modified PVDF powder;

[0021] (2) Preparation of PVDF-g-PAA

[0022] a. Add 1 g of modified PVDF powder to 20 mL of water / anhydrous ethanol, with a volume ratio of water to anhydrous ethanol of 1:1, and disperse evenly by ultrasonication. Then add 20 mg of azobisisobutyronitrile and 1 mL of acrylic monomer, and react at 70°C for 12 hours under a nitrogen atmosphere to carry out free radical polymerization.

[0023] b. Dilute the reaction solution with deionized water, then centrifuge it, and repeatedly wash and centrifuge it with deionized water to remove unreacted acrylic monomers. Finally, freeze-dry the obtained brown solid under vacuum for 24 hours to obtain dry PVDF-g-PAA powder.

[0024] (3) Preparation of PVDF-g-PAA / PAM polymer hydrogel adsorbent

[0025] a. First, 1000 mg of PVDF-g-PAA powder was ultrasonically dispersed and mixed with 5 mL of ultrapure water until homogeneous. Then, 15 mg of N,N′-methylenebisacrylamide, 15 mg of ammonium persulfate, and 1 g of acrylamide were added. After the drug was completely dissolved, the mixture was reacted at 60 °C for 4 hours under a nitrogen atmosphere.

[0026] b. After the reaction is complete, wash the surface of the PVDF-g-PAA / PAM polymer hydrogel adsorbent with deionized water.

[0027] Example 1 represents the optimal process parameters, resulting in an adsorption capacity increase of over 50% compared to other crosslinked materials (such as 4VP / DMAEMA). This material exhibits superior performance: a lithium adsorption capacity of 33.48 mg / g and a lithium-magnesium selectivity coefficient as high as 45, significantly outperforming existing manganese-based and titanium-based adsorbents (15-22 mg / g). Its three-dimensional network structure endows it with excellent mechanical properties, maintaining an adsorption capacity of 82% after 5 cycles, overcoming the bottleneck of traditional adsorbents' tendency to aggregate and deactivate. Compared to other comparative examples and embodiments, it demonstrates unexpected technical advantages.

[0028] To address the technical problem of this invention, another solution proposed by this invention is as follows: the application of the polyvinylidene fluoride-containing polymer hydrogel adsorbent in lithium ion adsorption.

[0029] Preferably, the hydrogel adsorbent is placed in a lithium-containing solution for 20-30 hours to achieve the adsorption of lithium ions.

[0030] Preferably, after the hydrogel adsorbent that has completed adsorption in the lithium-containing solution is removed and desorbed, it is placed in the next lithium-containing solution to adsorb lithium ions. This process is repeated multiple times to achieve cyclic adsorption of the hydrogel adsorbent.

[0031] Preferably, the prepared hydrogel adsorbent is placed in a lithium-containing solution with pH=10 and a lithium ion concentration of 300 mg / L to adsorb lithium ions. After adsorption is complete, the hydrogel adsorbent is removed and placed in a 1 mmol sulfuric acid solution for desorption. The desorbed hydrogel adsorbent is then placed in another 300 mg / L lithium-containing solution for a second adsorption. The above operation is repeated for five cycles. The initial adsorption capacity of the polyvinylidene fluoride polymer hydrogel adsorbent for lithium ions is 33.48 mg / g, and after five cycles, the adsorption capacity can still reach 27.45 mg / g.

[0032] The beneficial effects of this invention are as follows:

[0033] The present invention discloses a method for preparing a polyvinylidene fluoride (PVDF)-containing polymeric hydrogel adsorbent. Its advantage lies in using PVDF as a backbone, grafting polyacrylic acid to form an amphiphilic polymer, and then constructing a three-dimensional interpenetrating network with polyacrylamide. The CF bonds of PVDF interact with Li through strong electronegativity. + It forms specific coordination (hard acid-hard base interaction), preferentially adsorbing lithium ions; the carboxylic acid groups of PAA ionize under the high pH conditions of salt lake brine, enriching Li through electrostatic attraction. + This enhances the adsorption capacity; the flexible chains of PAM complement the rigid chains of PVDF, strengthening the mechanical properties of the hydrogel; the expansion / contraction of the PAM network regulates the pore structure, accelerating the adsorption of Li. + Diffusion; the chemical inertness of the CF bonds in PVDF resists Cl. - SO4 2- Corrosive ions are introduced to improve its stability in brine environments.

[0034] The polyvinylidene fluoride-containing hydrogel adsorbent synthesized by the method of this invention is simple and low in cost. This material exhibits excellent lithium-ion adsorption performance. Verification shows that its lithium-ion adsorption capacity in water reaches 33.48 mg / g at room temperature, a significant improvement compared to the 15 mg / g adsorption capacity in patent number CN108435142, the 17 mg / g adsorption capacity in patent number CN108126651, and the 22.05 mg / g adsorption capacity in patent number CN110898794. Its adsorption effect on other metal cations is relatively low; for example, the lithium-magnesium selectivity coefficient for magnesium ions can reach 45. It exhibits good adsorption performance in alkaline environments, making it highly suitable for the alkaline environment of salt lake brine. Furthermore, it is reusable, demonstrating good sustainability and significant application potential.

[0035] To address the problems of complex synthesis processes, high costs, and poor selectivity in existing adsorbents, this technology uses PVDF as a matrix and constructs a three-step interpenetrating network hydrogel: first, PVDF is modified with KOH / ethanol to introduce active double bonds; then, PAA is grafted using free radical polymerization to form an amphiphilic polymer; finally, it is cross-linked with AM to form a PVDF-g-PAA / PAM composite hydrogel. This material innovatively utilizes the CF bond of PVDF to specifically coordinate lithium ions, exhibiting superior performance in an alkaline environment (pH=10): a lithium adsorption capacity of 33.48 mg / g and a lithium-magnesium selectivity coefficient as high as 45, significantly outperforming existing manganese-based and titanium-based adsorbents (15-22 mg / g). Its three-dimensional network structure endows it with excellent mechanical properties, maintaining 82% of its adsorption capacity after 5 cycles, overcoming the bottleneck of traditional adsorbents' tendency to aggregate and deactivate. Experiments confirmed that the optimized KOH concentration (10%), reaction temperature (60 °C), and AM dosage (1 g), i.e., Example 1, were the best process parameters, resulting in an adsorption capacity increase of over 50% compared to other crosslinking materials (such as 4VP / DMAEMA). This technology uses inexpensive and readily available raw materials, and the process is simple and controllable, making it particularly suitable for lithium extraction from high magnesium-to-lithium ratio salt lake brines, providing a new approach for the development of clean energy materials. Attached Figure Description

[0036] Figure 1 A method for preparing a polyvinylidene fluoride (PVDF)-g-PAA polymer hydrogel adsorbent; Schematic diagram of the synthesis scheme of the amphiphilic polymer PVDF-g-PAA in Example 1.

[0037] Figure 2 A method for preparing a polyvinylidene fluoride (PVDF) polymer hydrogel adsorbent. The 1H NMR spectrum of PVDF-g-PAA prepared in Example 1.

[0038] Figure 3 A method for preparing a polyvinylidene fluoride (PVDF)-g-PAA / PAM polymeric hydrogel adsorbent. SEM image of the PVDF-g-PAA / PAM polymeric hydrogel adsorbent prepared in Example 1.

[0039] Figure 4 A method for preparing a polyvinylidene fluoride (PVDF)-g-PAA / PAM polymeric hydrogel adsorbent. The selective adsorption capacity of the PVDF-g-PAA / PAM polymeric hydrogel adsorbent prepared in Example 1 for lithium ions in a mixture of monovalent and divalent metals is shown in the figure.

[0040] Figure 5 A method for preparing a polyvinylidene fluoride (PVDF)-g-PAA / PAM polymer hydrogel adsorbent. Example 1 shows the adsorption capacity of the PVDF-g-PAA / PAM polymer hydrogel adsorbent as a function of adsorption time.

[0041] Figure 6A method for preparing a polyvinylidene fluoride (PVDF)-g-PAA / PAM polymer hydrogel adsorbent. The pseudo-first-order kinetic adsorption curve of the PVDF-g-PAA / PAM polymer hydrogel adsorbent prepared in Example 1.

[0042] Figure 7 A method for preparing a polyvinylidene fluoride (PVDF)-g-PAA / PAM polymer hydrogel adsorbent: Pseudo-second-order kinetic adsorption curve of the PVDF-g-PAA / PAM polymer hydrogel adsorbent prepared in Example 1.

[0043] Figure 8 A method for preparing a polyvinylidene fluoride (PVDF)-g-PAA / PAM polymer hydrogel adsorbent. Example 1: Isothermal adsorption curve of the PVDF-g-PAA / PAM polymer hydrogel adsorbent prepared.

[0044] Figure 9 A method for preparing a polyvinylidene fluoride (PVDF)-g-PAA / PAM polymer hydrogel adsorbent. Example 1: Adsorption capacity diagram of lithium ions for the PVDF-g-PAA / PAM polymer hydrogel adsorbent prepared at different pH values.

[0045] Figure 10 A method for preparing a polyvinylidene fluoride (PVDF)-g-PAA / PAM polymer hydrogel adsorbent. Example 1: Cyclic adsorption capacity diagram of the PVDF-g-PAA / PAM polymer hydrogel adsorbent prepared. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be further clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0047] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0048] Example 1

[0049] A method for preparing a polyvinylidene fluoride (PVDF)-containing polymer hydrogel adsorbent includes the following steps:

[0050] (1) Preparation of modified polyvinylidene fluoride (PVDF) powder

[0051] a. First, prepare 20 mL of a 10% KOH aqueous solution, then mix it with 20 mL of anhydrous ethanol at a volume ratio of 1:1. Disperse 10 g of polyvinylidene fluoride powder evenly in the above KOH / anhydrous ethanol mixture, stir magnetically to ensure thorough dispersion, and then stir at 60 °C for 10 min to obtain a brown solution.

[0052] b. The post-processing of the reaction solution includes the following steps: centrifugation to obtain the lower layer solid, washing with deionized water, ultrasonic dispersion, centrifugation again, and repeating this step until the solution is washed to neutral. The obtained solid is freeze-dried under vacuum for 24 hours to obtain modified PVDF powder.

[0053] (2) Preparation of PVDF-g-PAA

[0054] a. Add 1 g of modified PVDF powder to 20 mL of water / anhydrous ethanol (volume ratio of water to anhydrous ethanol is 1:1), disperse evenly by ultrasonication, then add 20 mg of azobisisobutyronitrile and 1 mL of acrylic monomer, and react at 70°C for 12 hours under nitrogen atmosphere to carry out free radical polymerization.

[0055] b. Dilute the reaction solution with deionized water, then centrifuge it, and repeatedly wash and centrifuge it with deionized water to remove unreacted acrylic monomers. Finally, freeze-dry the obtained brown solid under vacuum for 24 hours to obtain dry PVDF-g-PAA powder.

[0056] (3) Preparation of PVDF-g-PAA / PAM polymer hydrogel adsorbent

[0057] a. First, 1000 mg of PVDF-g-PAA powder was ultrasonically dispersed and mixed with 5 mL of ultrapure water until homogeneous. Then, 15 mg of N,N′-methylenebisacrylamide, 15 mg of ammonium persulfate, and 1 g of acrylamide were added. After the drug was completely dissolved, the mixture was reacted at 60 °C for 4 hours under a nitrogen atmosphere.

[0058] b. After the reaction is complete, wash the surface of the PVDF-g-PAA / PAM polymer hydrogel adsorbent with deionized water.

[0059] In this embodiment, the preparation route of PVDF-g-PAA is as follows: Figure 1 As shown, after the synthesis was completed, the final product of step (2) b was characterized by 1H NMR spectroscopy. The PVDF-g-PAA prepared in this example was dissolved in deuterated dimethyl sulfoxide, and then subjected to 1H NMR spectroscopy. 1 1H NMR spectroscopy test, 1 H NMR spectrum as shown Figure 2 As shown, this indicates that PVDF-g-PAA was successfully synthesized.

[0060] The PVDF-g-PAA / PAM polymeric hydrogel adsorbent prepared in this embodiment was frozen at -20 °C and then freeze-dried under vacuum for 24 hours. Scanning electron microscopy (SEM) was then performed, and the SEM images are shown below. Figure 3As shown, the hydrogel has a uniform pore distribution and pore size, which is beneficial for adsorbing lithium ions in water.

[0061] An application of a polyvinylidene fluoride (PVDF)-containing hydrogel adsorbent in the adsorption of lithium ions includes the following steps:

[0062] The hydrogel adsorbent prepared in Example 1 was placed in mixed solutions of lithium ions, sodium ions, potassium ions, magnesium ions, and calcium ions of different concentrations for 24 hours for adsorption. The hydrogel adsorbent prepared in Example 1 was also placed in lithium-containing solutions at different pH values ​​for adsorption. The hydrogel adsorbent prepared in Example 1 was placed in a lithium-containing solution at pH=10 for 24 hours, and the adsorption capacity of lithium ions at different time points was tested and fitted using pseudo-first-order and pseudo-second-order kinetic models. The hydrogel adsorbent prepared in Example 1 was placed in solutions of different lithium concentrations at pH=10, and the same operation was performed at 35 °C and 45 °C, except at room temperature (25 °C), and fitted using Langmuir and Freundlich models. The hydrogel adsorbent prepared in Example 1 was placed in a lithium-containing solution with a lithium ion concentration of 300 mg / L to adsorb lithium ions. After adsorption, the hydrogel adsorbent was removed and placed in a 1 mmol sulfuric acid solution for desorption. The desorbed hydrogel adsorbent was then placed in another 300 mg / L lithium-containing solution for a second adsorption. This process was repeated five times.

[0063] Summary: Results are attached. Figures 4-10 As shown. The results indicate that the hydrogel exhibits good selectivity for magnesium and calcium ions, with slightly higher selectivity for sodium and potassium ions, but overall it does not hinder the adsorption of lithium ions. The lithium-magnesium selectivity coefficient for magnesium ions can reach 45. The hydrogel adsorbent reaches adsorption equilibrium at 600 minutes, according to the pseudo-first-order kinetic model (…). Figure 6 ) and pseudo-second-order dynamics model ( Figure 7 The fitting results of the model leaned more towards a pseudo-second-order kinetic model, indicating that the adsorption of lithium ions by the polyvinylidene fluoride (PVDF) polymer hydrogel adsorbent was chemisorption. With increasing temperature, the adsorption capacity of lithium ions increased, indicating that heating was beneficial for lithium ion adsorption. The fitting results also leaned more towards the Langmuir model, suggesting monolayer adsorption. Alkaline conditions were more conducive to lithium ion adsorption, making it more suitable for the alkaline environment of salt lake brine. The initial adsorption capacity of the PVDF polymer hydrogel adsorbent for lithium ions was 33.48 mg / g, and after five cycles, the adsorption capacity still reached 27.45 mg / g. This indicates that the prepared hydrogel adsorbent has good cyclic adsorption performance and good sustainability; experiments showed that the adsorbent maintained 82% of its adsorption capacity after several cycles.

[0064] Example 2

[0065] The preparation method of a polyvinylidene fluoride (PVDF)-containing polymer hydrogel adsorbent is the same as that in Example 1, and will not be repeated here. The differences are as follows: the mass fraction of the KOH aqueous solution in step (1)a is 5%, and the volume ratio of water to anhydrous ethanol is 1:2; the amount of azobisisobutyronitrile (AIOBR) in step (2)a is 40 mg, the amount of acrylic acid is 2 mL, and the reaction time is 16 h; the amount of PVDF-g-PAA in step (3)a is 500 mg. The other steps are the same as in Example 1.

[0066] The application of a polyvinylidene fluoride (PVDF) polymer hydrogel adsorbent in the adsorption of lithium ions is described below. Except that the gel used is prepared in Example 2, the other steps are the same as in Example 1 and will not be repeated here.

[0067] Summary: The polyvinylidene fluoride (PVDF)-containing hydrogel adsorbent prepared in Example 2 exhibits good selective adsorption of lithium ions, conforming to both the second-order kinetic model and the Langmuir model. In a lithium-containing solution at pH 10 and 300 mg / L, the adsorption capacity for lithium ions is 22.35 mg / g, decreasing to 18.11 mg / g after five cycles. The decrease in adsorption capacity due to the reduction in PVDF-g-PAA dosage indicates a close correlation between fluorine content and adsorption capacity.

[0068] Example 3

[0069] The preparation method of a polyvinylidene fluoride (PVDF)-containing polymer hydrogel adsorbent is the same as that in Example 1, and will not be repeated here. The differences are as follows: the mass fraction of the KOH aqueous solution in step (1)a is 20%, and the reaction time is 15 min; the reaction temperature in step (2)a is 80 °C, and the reaction time is 8 h; the amount of PVDF-g-PAA used in step (3)a is 1500 mg. The other steps are the same as in Example 1.

[0070] The application of a polyvinylidene fluoride (PVDF) polymer hydrogel adsorbent in the adsorption of lithium ions is described below. Except that the gel used is prepared in Example 3, the other steps are the same as in Example 1 and will not be repeated here.

[0071] In summary, the prepared polyvinylidene fluoride (PVDF)-containing hydrogel adsorbent exhibits good selective adsorption of lithium ions, conforming to both the second-order kinetic model and the Langmuir model. The adsorption capacity for lithium ions in a lithium-containing solution at pH 10 and 300 mg / L is 38.09 mg / g, decreasing to 32.76 mg / g after five cycles. This example demonstrates the highest adsorption capacity, but the excessive use of PVDF-g-PAA does not significantly enhance performance. Considering economic efficiency, the dosage used in Example 1 is optimal.

[0072] Example 4

[0073] The preparation method of a polyvinylidene fluoride (PVDF) polymer hydrogel adsorbent is the same as that in Example 1, and will not be repeated here. The differences are as follows: in step (1)a, the mass fraction of the KOH aqueous solution is 15%, the reaction temperature is 40 °C, and the reaction time is 30 min; in step (2)a, the reaction temperature is 60 °C and the reaction time is 24 h; in step (3)a, the reaction temperature is 50 °C and the reaction time is 6 h. The other steps are the same as in Example 1.

[0074] The application of a polyvinylidene fluoride (PVDF) polymer hydrogel adsorbent in the adsorption of lithium ions is described below. Except that the gel used is prepared as in Example 4, the other steps are the same as in Example 1 and will not be repeated here.

[0075] In summary, the prepared polyvinylidene fluoride (PVDF)-containing hydrogel adsorbent exhibits good selective adsorption of lithium ions, conforming to both the second-order kinetic model and the Langmuir model. The adsorption capacity for lithium ions in a lithium-containing solution at pH 10 and 300 mg / L is 32.58 mg / g, decreasing to 27.69 mg / g after five cycles. The amount of PVDF-g-PAA used was the same as in Example 1, with minimal change in adsorption capacity. The slight alterations in the reaction temperature and time for gel formation indicate that this gel is easy to prepare, less demanding in terms of reaction temperature and time, and more conducive to large-scale production.

[0076] Comparative Example 1

[0077] A method for preparing a polyvinylidene fluoride (PVDF)-containing polymer hydrogel adsorbent includes the following steps:

[0078] The preparation method of the adsorbent is basically the same as in Example 1, except that acrylamide is replaced with 4-vinylpyridine (4VP) to prepare PVDF-g-PAA / P4VP polymer hydrogel adsorbent.

[0079] The application of a polyvinylidene fluoride-containing polymer hydrogel adsorbent in the adsorption of lithium ions is basically the same as that in Example 1, and will not be repeated here.

[0080] In summary, the prepared polyvinylidene fluoride (PVDF)-containing hydrogel adsorbent exhibits good selective adsorption of lithium ions, conforming to both the second-order kinetic model and the Langmuir model. The adsorption capacity for lithium ions in a lithium-containing solution at pH 10 and 300 mg / L is 20.32 mg / g, decreasing to 16.25 mg / g after five cycles. The hydrogel formed using P4VP shows inferior absorption and swelling effects compared to the hydrogel formed using PAM, resulting in a decrease in adsorption capacity. Furthermore, AM is significantly cheaper than 4VP.

[0081] Comparative Example 2

[0082] A method for preparing a polyvinylidene fluoride (PVDF)-containing polymer hydrogel adsorbent includes the following steps:

[0083] The preparation method of the adsorbent is basically the same as in Example 1, except that acrylamide is replaced with dimethylaminoethyl methacrylate (DMAEMA) to prepare PVDF-g-PAA / PDMAEMA polymeric hydrogel adsorbent.

[0084] The application of a polyvinylidene fluoride-containing polymer hydrogel adsorbent in the adsorption of lithium ions is basically the same as that in Example 1, and will not be repeated here.

[0085] In summary, the prepared polyvinylidene fluoride (PVDF)-containing hydrogel adsorbent exhibits good selective adsorption of lithium ions, conforming to both the second-order kinetic model and the Langmuir model. The adsorption capacity for lithium ions in a lithium-containing solution at pH 10 and 300 mg / L is 23.41 mg / g, decreasing to 18.84 mg / g after five cycles. The hydrogel formed using PDMAEMA shows inferior absorption and swelling effects compared to that formed using PAM, resulting in a decrease in adsorption capacity. Furthermore, AM is less expensive than DMAEMA.

[0086] In summary, this invention discloses a method for preparing a highly efficient and selective lithium-ion adsorbent and its application, belonging to the field of lithium adsorption material technology. Addressing the problems of complex synthesis processes, high costs, and poor selectivity in existing adsorbents, this technology uses PVDF as a matrix and constructs a three-dimensional interpenetrating network hydrogel through a three-step method: first, PVDF is modified with KOH / ethanol to introduce active double bonds; then, PAA is grafted using free radical polymerization to form an amphiphilic polymer; finally, it is cross-linked with AM to form a PVDF-g-PAA / PAM composite hydrogel. This material innovatively utilizes the CF bond of PVDF to specifically coordinate lithium ions, exhibiting superior performance in an alkaline environment (pH=10): a lithium adsorption capacity of 33.48 mg / g and a lithium-magnesium selectivity coefficient as high as 45, significantly better than existing manganese-based and titanium-based adsorbents (15-22 mg / g). Its three-dimensional network structure endows it with excellent mechanical properties, maintaining an adsorption capacity of 82% after 5 cycles, overcoming the bottleneck of easy aggregation and deactivation of traditional adsorbents. Experiments confirmed that the optimized KOH concentration (10%), reaction temperature (60℃), and AM dosage (1 g), i.e., Example 1, were the best process parameters, resulting in an adsorption capacity increase of over 50% compared to other crosslinking materials (such as 4VP / DMAEMA). This technology uses inexpensive and readily available raw materials, and the process is simple and controllable, making it particularly suitable for lithium extraction from high magnesium-to-lithium ratio salt lake brines, providing a new approach for the development of clean energy materials.

[0087] The embodiments disclosed in this invention are intended to exemplify the technical concept and implementation path of this invention, and are not an exhaustive list of all possible forms. Those skilled in the art, having fully understood the inventive essence of this invention, can make adaptive adjustments to the specific implementation structure, material selection, or process parameters, including but not limited to replacing some feature elements with equivalent technical means. Any reasonable extension, combination optimization, or application scenario expansion based on the core idea of ​​this technical solution, as long as it does not depart from the protection scope defined by the claims, shall be deemed to fall within the legal protection radius of this patent.

Claims

1. A method for preparing a polyvinylidene fluoride (PVDF)-containing polymeric hydrogel adsorbent, characterized in that, Includes the following steps: (1) Preparation of modified polyvinylidene fluoride (PVDF) powder a. First, prepare a KOH aqueous solution with a mass fraction of 5-20%, then mix it with anhydrous ethanol at a volume ratio of 1:0.5-3; uniformly disperse polyvinylidene fluoride powder in the above KOH / anhydrous ethanol mixed solution, stir magnetically to ensure full dispersion, and then stir at 40-70 °C to obtain a brown solution; b. The post-processing of the reaction solution includes the following steps: centrifugation to obtain the lower layer solid, washing with deionized water, ultrasonic dispersion, centrifugation again, repeating this step until the solution is washed to neutral, and freeze-drying the obtained solid under vacuum to obtain modified PVDF powder; (2) Preparation of PVDF-g-PAA a. Add the modified PVDF powder to a water / anhydrous ethanol mixture with a volume ratio of water to anhydrous ethanol of 1:0.5-3, disperse it evenly by ultrasonication, then add azobisisobutyronitrile and acrylic acid monomer, and carry out free radical polymerization at 60-80 °C under a nitrogen atmosphere. b. Dilute the reaction solution with deionized water, then centrifuge it, and repeatedly wash and centrifuge it with deionized water to remove unreacted acrylic monomers. Finally, freeze-dry the obtained brown solid under vacuum to obtain dry PVDF-g-PAA powder. (3) Preparation of PVDF-g-PAA / PAM polymer hydrogel adsorbent a. First, ultrasonically disperse and mix PVDF-g-PAA with ultrapure water until uniform, then add N,N′-methylenebisacrylamide, ammonium persulfate, and acrylamide. After the drug is completely dissolved, react at 50-70 °C under a nitrogen atmosphere. b. After the reaction is complete, the surface of the PVDF-g-PAA / PAM polymer hydrogel adsorbent is washed with deionized water.

2. The method for preparing the polyvinylidene fluoride-containing polymer hydrogel adsorbent according to claim 1, characterized in that, In step (1)a, the mass fraction of KOH aqueous solution is 10%; the volume ratio of KOH aqueous solution to anhydrous ethanol in step (1)a is 1:1; the reaction temperature in step (1)a is 60 °C; the volume ratio of water to anhydrous ethanol in step (2)a is 1:1; the reaction temperature in step (2)a is 70 °C; in step (3)a, PVDF-g-PAA is 1000 mg, ultrapure water is 5 mL, N,N′-methylenebisacrylamide is 15 mg, ammonium persulfate is 15 mg, and acrylamide is 1000 mg; the reaction temperature in step (3)a is 60 °C.

3. The method for preparing the polyvinylidene fluoride-containing polymer hydrogel adsorbent according to claim 1, characterized in that, Includes the following steps: (1) Preparation of modified polyvinylidene fluoride (PVDF) powder a. First, prepare 20 mL of 10% KOH aqueous solution, then mix it with 20 mL of anhydrous ethanol at a volume ratio of 1:

1. Disperse 10 g of polyvinylidene fluoride powder evenly in the above KOH / anhydrous ethanol mixed solution, stir magnetically to ensure full dispersion, and then stir at 60 °C for 10 min to obtain a brown solution. b. The post-processing of the reaction solution includes the following steps: centrifugation to obtain the lower layer solid, washing with deionized water, ultrasonic dispersion, centrifugation again, repeating this step until the solution is washed to neutral, and freeze-drying the obtained solid under vacuum for 24 hours to obtain modified PVDF powder; (2) Preparation of PVDF-g-PAA a. Add 1 g of modified PVDF powder to 20 mL of water / anhydrous ethanol, with a volume ratio of water to anhydrous ethanol of 1:1, and disperse evenly by ultrasonication. Then add 20 mg of azobisisobutyronitrile and 1 mL of acrylic monomer, and react at 70 °C for 12 hours under a nitrogen atmosphere to carry out free radical polymerization. b. Dilute the reaction solution with deionized water, then centrifuge it, and repeatedly wash and centrifuge it with deionized water to remove unreacted acrylic monomers. Finally, freeze-dry the obtained brown solid under vacuum for 24 hours to obtain dry PVDF-g-PAA powder. (3) Preparation of PVDF-g-PAA / PAM polymer hydrogel adsorbent a. First, 1000 mg of PVDF-g-PAA powder was ultrasonically dispersed and mixed with 5 mL of ultrapure water until homogeneous. Then, 15 mg of N,N′-methylenebisacrylamide, 15 mg of ammonium persulfate, and 1 g of acrylamide were added. After the drug was completely dissolved, the mixture was reacted at 60 °C for 4 hours under a nitrogen atmosphere. b. After the reaction is complete, the surface of the PVDF-g-PAA / PAM polymer hydrogel adsorbent is washed with deionized water.

4. The application of the polyvinylidene fluoride-containing polymer hydrogel adsorbent prepared by any one of claims 1-3 in lithium ion adsorption.

5. The application of the polyvinylidene fluoride-containing polymer hydrogel adsorbent according to claim 4 in lithium ion adsorption, characterized in that: The hydrogel adsorbent is placed in a lithium-containing solution for 20-30 hours to achieve the adsorption of lithium ions.

6. The application of the polyvinylidene fluoride-containing polymer hydrogel adsorbent according to claim 4 in lithium ion adsorption, characterized in that: After the hydrogel adsorbent that has completed adsorption in the lithium-containing solution is removed and desorbed, it is placed in the next lithium-containing solution to adsorb lithium ions. This process is repeated multiple times to achieve cyclic adsorption of the hydrogel adsorbent.

7. The application of the polyvinylidene fluoride-containing hydrogel adsorbent prepared according to claim 3 in lithium ion adsorption, characterized in that: The prepared hydrogel adsorbent was placed in a lithium-containing solution with pH=10 and a lithium ion concentration of 300 mg / L to adsorb lithium ions. After the adsorption was completed, the hydrogel adsorbent was taken out and placed in 1 mmol of sulfuric acid solution for desorption. The desorbed hydrogel adsorbent was then placed in another 300 mg / L lithium-containing solution for a second adsorption. The above operation was repeated five times. The initial adsorption capacity of the polyvinylidene fluoride (PVDF) polymer hydrogel adsorbent for lithium ions was 33.48 mg / g, and after five cycles, the adsorption capacity still reached 27.45 mg / g.

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