Preparation method and application of ion specific effect regulation gradient polyelectrolyte hydrogel

Abstract

The invention belongs to the technical field of hydrogel material preparation and application, and relates to a preparation method and application of an ion specific effect regulation gradient polyelectrolyte hydrogel, and the preparation method comprises the following steps: dispersing methacrylic acid, acrylamide, a cross-linking agent, a photoinitiator and a light absorber in ultrapure water to obtain a reaction mixed solution; injecting into a glass plate mold clamped with a silica gel gasket, and irradiating with ultraviolet light; and soaking the reacted material in a salt solution for gelation reaction to obtain the ion specific effect regulation gradient polyelectrolyte hydrogel. The gradient polyelectrolyte hydrogel regulated and controlled by the ion specificity effect is prepared through a one-step method, and the preparation method is simple, low in cost and suitable for large-scale production; meanwhile, the prepared gradient polyelectrolyte hydrogel regulated and controlled by the ion specificity effect can change the network chain density and gradient distribution, self-driven enrichment and removal of low-concentration (0.5-2 mg / L) lithium ions are realized, and the self-driven enrichment efficiency is improved.

Description

Technical field:

[0001] The present invention belongs to the technical field of hydrogel material preparation and application, and relates to a hydrogel material enriched with low-concentration lithium ions. Specifically, it relates to a preparation method and application of a gradient polyelectrolyte hydrogel with ion-specific effect regulation, which realizes self-driven enrichment of low-concentration lithium ions based on the interface and built-in electrostatic field of the gradient polyelectrolyte hydrogel. Background technology:

[0002] With the rapid development of the global clean energy and power battery industries, the demand for lithium resources has increased exponentially. Seawater contains about 230 billion tons of lithium resources, but its lithium concentration is extremely low, about 0.17ppm. Existing traditional processes still have problems in extracting lithium from low-concentration lithium solutions. For example, membrane separation methods have poor selectivity for monovalent ions and poor separation performance due to concentration polarization. Lithium ion sieve adsorption method for Li + It has good selectivity, but is mainly used in high-concentration lithium-rich brine. Traditional electrochemical methods face the challenge of high energy consumption.

[0003] Currently, most studies tend to use photothermal drive to reduce the energy consumption in the lithium ion enrichment process, but its effectiveness still depends on external stimulation and has not yet achieved true self-driven enrichment of low-concentration lithium ions. Gradient polyelectrolyte hydrogels are three-dimensional network materials with a gradient distribution of chain groups, in which the diffusion of counterions can generate interfaces and built-in electrostatic fields. They have been widely used in the directional transport of ions and self-driven enrichment. However, a large number of ionizable groups will generate high osmotic pressure, making the hydrogel prone to swelling at certain pH values, ultimately weakening the gradient distribution of the hydrogel.

[0004] Therefore, in order to address the problem of low self-driven enrichment efficiency of existing traditional lithium extraction processes under low lithium ion concentration conditions, the present invention innovatively proposes an ion-specific effect-regulated gradient polyelectrolyte hydrogel for self-driven enrichment of low-concentration lithium ions. Summary of the invention:

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide an ion-specific effect regulated gradient polyelectrolyte hydrogel to improve the self-driven enrichment efficiency of the hydrogel in low concentration lithium ions.

[0006] In order to achieve the above object, the present invention provides a method for preparing a gradient polyelectrolyte hydrogel with ion-specific effect regulation, the specific steps comprising:

[0007] (1) dispersing methacrylic acid, acrylamide, a crosslinking agent, a photoinitiator, and a light absorber in ultrapure water and stirring to obtain a reaction mixture solution;

[0008] (2) The reaction mixture was injected into a glass plate mold with a silicone gasket and irradiated with ultraviolet light for 4-5 hours;

[0009] (3) After the reaction is completed, the reacted material is immersed in a salt solution to undergo a gelation reaction, thereby obtaining a gradient polyelectrolyte hydrogel with ion-specific effects regulated.

[0010] Furthermore, the total molar concentration of methacrylic acid and acrylamide in the reaction mixture is 5-8 mol / L, and the molar concentration ratio is 1:(0.5-2). Preferably, the total molar concentration of methacrylic acid and acrylamide in the reaction mixture is 5 mol / L, and the molar concentration ratio is 2:1.

[0011] Furthermore, in step (1), the crosslinking agent is N,N-methylenebis(acrylamide), and its concentration in the reaction mixture is 25-150 mM. The photoinitiator is α-ketoglutaric acid, and its concentration in the reaction mixture is 0.1-0.2 wt%. The light absorber is purchased from Shandong Huaen Rubber and Plastic New Materials Co., Ltd., and its product name is water-based ultraviolet light absorber. The concentration in the reaction mixture is 0.2-0.4 wt%.

[0012] Preferably, in the reaction mixture, the concentration of the cross-linking agent is 75 mM, and the concentration of the photoinitiator is 0.2 wt %.

[0013] Furthermore, in step (2), the glass plate is soda-lime glass, and the thickness of the silicone gasket is 2 mm.

[0014] Furthermore, the gelation reaction in step (3) is performed by soaking the reacted material in a salt solution for 24 hours; the salt solution is an aqueous solution of MgSO4, Na2SO4, NaCl or NaI, with a concentration of 0.5 to 2.5 mol / L. Preferably, the salt solution is an aqueous solution of Na2SO4, with a concentration of 1 to 1.5 mol / L.

[0015] The present invention also provides a gradient polyelectrolyte hydrogel obtained by the above preparation method and regulated by ion-specific effects.

[0016] The present invention also provides the application of the gradient polyelectrolyte hydrogel regulated by the ion-specific effect in the extraction of lithium resources.

[0017] The application is to use a gradient polyelectrolyte hydrogel regulated by ion-specific effects in a lithium-containing solution, which can achieve self-driven enrichment of lithium ions with high enrichment efficiency and high selectivity for lithium ions; in particular, the self-driven enrichment efficiency is high for low-concentration (0.5-2 mol / L) lithium ions; and the enriched lithium ions can be automatically removed.

[0018] The present invention also provides the use of the gradient polyelectrolyte hydrogel regulated by the ion-specific effect in the adsorption of metal ions, wherein the metal ions include but are not limited to lithium ions, sodium ions, potassium ions, calcium ions and magnesium ions.

[0019] The gradient polyelectrolyte hydrogel regulated by the ion-specific effect described in the present invention has a wide range of applications in the extraction of lithium resources. The reasons are as follows: (1) The polyelectrolyte forms an electrostatic field around it due to the diffusion of counterions, and at the same time forms an electrostatic field based on the built-in chemical gradient of the hydrogel. Based on the action of these two electrostatic forces, the self-driven enrichment of lithium ions is successfully achieved. (2) The gradient polyelectrolyte hydrogel regulated by the ion-specific effect prepared by the present invention can improve the self-driven enrichment efficiency of low-concentration lithium ions by optimizing the network chain density and gradient structure distribution. (3) The gradient polyelectrolyte hydrogel regulated by the ion-specific effect prepared by the present invention has pH responsiveness and can achieve automatic removal of enriched lithium ions under conditions below the carboxyl pKa value. (4) This strategy has universal applicability.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The preparation method of the present invention is simple and the raw materials are cheap. The gradient polyelectrolyte hydrogel prepared from methacrylic acid and acrylamide is regulated by salt soaking method and is recyclable.

[0022] (2) The gradient polyelectrolyte hydrogel regulated by the ion-specific effect prepared by the present invention can achieve self-driven enrichment of low-concentration lithium ions through the interface and built-in potential.

[0023] (3) The gradient polyelectrolyte hydrogel regulated by the ion-specific effect prepared by the present invention can improve the self-driven enrichment efficiency of low-concentration lithium ions by optimizing the network chain density and gradient structure distribution.

[0024] (4) The gradient polyelectrolyte hydrogel regulated by the ion-specific effect prepared by the present invention has pH responsiveness and can automatically remove the enriched lithium ions under conditions lower than the pKa of the carboxyl group.

[0025] In summary, the present invention prepares a gradient polyelectrolyte hydrogel regulated by ion-specific effects through a one-step method. The preparation method is simple, low-cost, and suitable for large-scale production. At the same time, the prepared gradient polyelectrolyte hydrogel regulated by ion-specific effects can change the network chain density and gradient distribution, realize self-driven enrichment and removal of low-concentration (0.5-2 mg / L) lithium ions, improve the self-driven enrichment efficiency, and the enrichment rate reaches up to 80%. Description of the drawings:

[0026] Figure 1This is a scanning electron microscope photograph of the gradient polyelectrolyte hydrogel after ion-specific effect regulation obtained in Example 1 of the present invention.

[0027] Figure 2 This is a schematic diagram of the test results of Example 5 of the present invention on the influence of different salt solutions on the internal potential of the gradient polyelectrolyte hydrogel.

[0028] Figure 3 This is a schematic diagram of the test results of Example 6 of the present invention on the effects of different salt solutions on the charge density of gradient polyelectrolyte hydrogels under acidic and alkaline conditions.

[0029] Figure 4 This is a schematic diagram of the experimental results of Example 7 of the present invention on the lithium enrichment performance of the gradient polyelectrolyte hydrogel in lithium solutions of different concentrations before and after regulation by Na2SO4.

[0030] Figure 5 This is a schematic diagram of the test results of Example 8 of the present invention on the lithium enrichment performance of the gradient polyelectrolyte hydrogel in lithium solutions of different concentrations before and after regulation by different concentrations of Na2SO4.

[0031] Figure 6 This is a schematic diagram of the experimental results of lithium removal from the gradient polyelectrolyte hydrogel before and after regulation by Na2SO4 in Example 9 of the present invention.

[0032] Figure 7 This is a diagram of the reverse electrodialysis device involved in the present invention.

[0033] Figure 8 The gradient polyelectrolyte hydrogel of Example 10 of the present invention is not regulated by Na2SO4 to Li + Schematic diagram of the IV curve results of / Y (Y represents other metal ions) solution.

[0034] Figure 9 The gradient polyelectrolyte hydrogel regulated by Na2SO4 in Example 10 of the present invention is Li + Schematic diagram of the IV curve results of / Y (Y represents other metal ions) solution.

[0035] Figure 10 The gradient polyelectrolyte hydrogel of Example 10 before and after Na2SO4 regulation of Li + / Y (Y represents other metal ions) selectivity experimental results schematic diagram. Specific implementation method:

[0036] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0037] Example 1:

[0038] This embodiment relates to a method for preparing a gradient polyelectrolyte hydrogel after regulated ion-specific effect, and the specific steps include:

[0039] (1) Weigh 5.74 g of methacrylic acid, 2.36 g of acrylamide, 0.028 g of α-ketoglutaric acid, 0.02 g of a light absorber, and 0.023 g of N,N-methylenebis(acrylamide) and disperse them in 20 mL of ultrapure water. Stir evenly to obtain a mixed solution.

[0040] (2) The mixed solution was injected into a mold and irradiated with ultraviolet light on one side (above the mold) for 5 h at room temperature to obtain a gradient polyelectrolyte hydrogel;

[0041] (3) The mold is disassembled, and the obtained gradient polyelectrolyte hydrogel is immersed in a 1 mol / L Na2SO4 aqueous solution for 24 h to perform a gelation reaction, thereby obtaining a gradient polyelectrolyte hydrogel regulated by Na2SO4, that is, a gradient polyelectrolyte hydrogel regulated by an ion-specific effect.

[0042] The Na2SO4 solution with a concentration of 1 mol / L was prepared by dissolving 14.2 g of Na2SO4 in 100 mL of ultrapure water.

[0043] The mold is composed of two sheets of soda-lime glass and a silicone gasket. The silicone gasket is placed between the two sheets of soda-lime glass and clamped around them with clips. The thickness of the silicone gasket is 2 mm.

[0044] The light absorber described in this embodiment was purchased from Shandong Huaen Rubber and Plastic New Materials Co., Ltd., and the product name is water-based ultraviolet light absorber.

[0045] In this example, the gradient polyelectrolyte hydrogel obtained by the above method after the ion-specific effect was regulated was characterized by SEM scanning electron microscopy. The cross-section of the gradient polyelectrolyte hydrogel after the ion-specific effect was magnified 200 times and 10,000 times, respectively. Figure 1 As shown. Figure 1 It can be observed that the pore size is distributed in a gradient manner.

[0046] Example 2:

[0047] This embodiment relates to a method for preparing a gradient polyelectrolyte hydrogel with ion-specific effect regulation, and the specific steps include:

[0048] (1) Methacrylic acid, acrylamide, N,N-methylenebis(acrylamide), α-ketoglutaric acid, and a light absorber are dispersed in ultrapure water and stirred to obtain a reaction mixture solution; the total molar concentration of methacrylic acid and acrylamide in the reaction mixture solution is 8 mol / L, and the molar concentration ratio is 1:1; in the reaction mixture solution, the concentration of N,N-methylenebis(acrylamide) is 25 mM; the concentration of α-ketoglutaric acid is 0.1 wt%; and the concentration of the light absorber is 0.2 wt%;

[0049] (2) The reaction mixture was injected into a glass plate mold with a silicone gasket of 2 mm thickness; the reaction was carried out under ultraviolet light for 4 h;

[0050] (3) After the reaction is completed, the reacted material is immersed in a 0.5 mol / L Na2SO4 aqueous solution for 24 h to undergo a gelation reaction to obtain an ion-specific effect-regulated gradient polyelectrolyte hydrogel.

[0051] The light absorber described in this embodiment was purchased from Shandong Huaen Rubber and Plastic New Materials Co., Ltd., and the product name is water-based ultraviolet light absorber.

[0052] Example 3:

[0053] This embodiment relates to a method for preparing a gradient polyelectrolyte hydrogel with ion-specific effect regulation, and the specific steps include:

[0054] (1) Methacrylic acid, acrylamide, N,N-methylenebis(acrylamide), α-ketoglutaric acid, and a light absorber are dispersed in ultrapure water and stirred to obtain a reaction mixture solution; the total molar concentration of methacrylic acid and acrylamide in the reaction mixture solution is 6 mol / L, and the molar concentration ratio is 1:2; in the reaction mixture solution, the concentration of N,N-methylenebis(acrylamide) is 150 mM; the concentration of α-ketoglutaric acid is 0.2 wt%; and the concentration of the light absorber is 0.4 wt%;

[0055] (2) The reaction mixture was injected into a glass plate mold with a silicone gasket of 2 mm thickness; the reaction was carried out under ultraviolet light for 5 h;

[0056] (3) After the reaction, the reacted material was immersed in a 2.5 mol / L Na2SO4 aqueous solution for 24 h to undergo a gelation reaction to obtain a gradient polyelectrolyte hydrogel with ion-specific effects.

[0057] The light absorber described in this embodiment was purchased from Shandong Huaen Rubber and Plastic New Materials Co., Ltd., and the product name is water-based ultraviolet light absorber.

[0058] Example 4:

[0059] This embodiment relates to a method for preparing a gradient polyelectrolyte hydrogel with ion-specific effect regulation, and the specific steps include:

[0060] (1) Methacrylic acid, acrylamide, N,N-methylenebis(acrylamide), α-ketoglutaric acid, and a light absorber are dispersed in ultrapure water and stirred to obtain a reaction mixture solution; the total molar concentration of methacrylic acid and acrylamide in the reaction mixture solution is 5 mol / L, and the molar concentration ratio is 1:1.5; in the reaction mixture solution, the concentration of N,N-methylenebis(acrylamide) is 100 mM; the concentration of α-ketoglutaric acid is 0.1 wt%; and the concentration of the light absorber is 0.3 wt%;

[0061] (2) The reaction mixture was injected into a glass plate mold with a silicone gasket of 2 mm thickness; the reaction was carried out under ultraviolet light for 5 h;

[0062] (3) After the reaction, the reacted material was immersed in a 1.5 mol / L Na2SO4 aqueous solution for 24 h to undergo a gelation reaction, thereby obtaining a gradient polyelectrolyte hydrogel with ion-specific effects.

[0063] The light absorber described in this embodiment was purchased from Shandong Huaen Rubber and Plastic New Materials Co., Ltd., and the product name is water-based ultraviolet light absorber.

[0064] Example 5:

[0065] This example involves an experiment on the effect of different salt solutions on the internal potential of a gradient polyelectrolyte hydrogel. The steps for preparing the gradient polyelectrolyte hydrogel after the ion-specific effect is regulated are as follows:

[0066] (1) A gradient polyelectrolyte hydrogel was prepared according to steps (1)-(2) of Example 1;

[0067] (2) The obtained gradient polyelectrolyte hydrogel was immersed in 1 mol / L Na2SO4, NaCl, and NaI aqueous solutions for 24 h.

[0068] The hydrogels soaked in Na2SO4, NaCl, and NaI aqueous solutions and the hydrogels not soaked in salt (control sample) were cut into 1.5 cm × 1.5 cm sizes and placed in a reverse electrodialysis device to test their internal potential using a digital source meter. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that the internal potential of the hydrogel after treatment with salt solution conforms to the Hofmeister anion sequence: SO4 2- >Cl - >I - , and the internal potential of the hydrogel was the largest after treatment with Na2SO4, indicating that the gradient structure was optimized.

[0069] Example 6:

[0070] This example involves the effect of different salt solutions on the charge density of gradient polyelectrolyte hydrogels under acidic and alkaline conditions. The gradient polyelectrolyte hydrogel prepared in Example 5, which was ion-specifically regulated by soaking in different salt solutions, and the gradient polyelectrolyte hydrogel without salt soaking (control sample) were weighed 1 g each, cut into pieces, and placed in 10 mL of ultrapure water for 24 hours. The supernatant was taken to measure the zeta potential. The results are shown as follows: Figure 3 As shown. Figure 3 It can be seen that the hydrogel is negatively charged under the condition of pH = 2 aqueous solution and negatively charged under the condition of pH = 11 aqueous solution, indicating that the hydrogel has pH responsiveness. In addition, the Zeta potential of the hydrogel after salt solution treatment also conforms to the Hofmeister anion sequence: SO4 2- >Cl - >I - The zeta potential of the hydrogel after Na2SO4 treatment was the highest, indicating that the hydrogel treated with Na2SO4 has a high density of ionizable groups and a high charge density, which is conducive to the enrichment and removal of lithium ions under different conditions. Since the hydrogel treated with Na2SO4 has the highest internal potential and zeta potential, sodium sulfate-modulated gradient polyelectrolyte hydrogel was selected for lithium enrichment testing.

[0071] Example 7:

[0072] This example involves a test on the effect of gradient polyelectrolyte hydrogels before and after Na2SO4 regulation on lithium enrichment performance in lithium solutions of different concentrations. 0.5 g of the gradient polyelectrolyte hydrogel regulated by Na2SO4 (referred to as Na2SO4) and the gradient polyelectrolyte hydrogel without Na2SO4 regulation (control sample) prepared in Example 1 were weighed and placed in 10 mL of lithium chloride aqueous solution with concentrations of 0.5 mg / L, 1 mg / L, 5 mg / L, and 10 mg / L, respectively, and shaken for 24 hours. The supernatant was taken and the enrichment rate of Li was measured as shown below. Figure 4 As shown. Figure 4 It can be seen that in lithium solutions of different concentrations, the enrichment efficiency of the hydrogel regulated by Na2SO4 is significantly improved compared with the unregulated hydrogel. This is because the carboxyl groups in the hydrogel interact with Li + It has electrostatic attraction and coordination effect, and the amide group and Li + Therefore, after the regulation of Na2SO4, the increase in the density of these ionizable groups and the increase in the built-in potential are beneficial to the improvement of lithium enrichment efficiency.

[0073] Example 8:

[0074] This embodiment involves a test of the lithium enrichment performance of a gradient polyelectrolyte hydrogel before and after regulation of different concentrations of Na2SO4 in lithium solutions of different concentrations. The preparation steps of the gradient polyelectrolyte hydrogel after regulation of different concentrations of Na2SO4 in this embodiment are as follows:

[0075] (1) A gradient polyelectrolyte hydrogel was prepared according to steps (1)-(2) of Example 1;

[0076] (2) The obtained gradient polyelectrolyte hydrogel was immersed in 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, and 2.5 mol / L Na2SO4 aqueous solutions for 24 h to obtain gradient polyelectrolyte hydrogels regulated by different concentrations of Na2SO4.

[0077] 0.5 g of the prepared gradient polyelectrolyte hydrogels regulated by different concentrations of Na2SO4 and the gradient polyelectrolyte hydrogels without Na2SO4 regulation were weighed and placed in a 10 mL lithium chloride aqueous solution with concentrations of 0.5 mg / L, 1 mg / L, and 2 mg / L, respectively, and shaken for 24 h. The supernatant was taken and the enrichment rate of Li was measured. The results are as follows: Figure 5 As shown. Figure 5 It can be seen that with the increase of Na2SO4 concentration, the lithium enrichment efficiency of the gradient hydrogel first increases and then decreases. In particular, it has a high enrichment performance for ultra-low concentration lithium (0.5mg / L), with the enrichment rate reaching up to 80%. This is because as the Na2SO4 concentration increases, the electrostatic shielding effect is enhanced, resulting in a decrease in lithium enrichment performance.

[0078] Example 9:

[0079] This example relates to an experiment on lithium removal by gradient polyelectrolyte hydrogel before and after regulation by Na2SO4. 0.5 g of the gradient polyelectrolyte hydrogel after ion-specific effect regulation prepared in Example 1 was weighed and placed in a 10 mL lithium chloride aqueous solution with initial concentrations C0 of 0.5 mg / L, 1 mg / L, 5 mg / L, and 10 mg / L, respectively. After shaking for 24 hours, the supernatant was collected and the lithium concentration was measured and recorded as C E Then, the lithium-enriched hydrogel was placed in 10 mL of HCl aqueous solution with a pH of 2 and shaken for 24 h. The supernatant was taken and the lithium concentration was measured and recorded as C. R , according to the formula The removal rate was calculated. The gradient polyelectrolyte hydrogel without Na2SO4 regulation was used as the control sample. The results are shown in Figure 2. Figure 6 As shown. Figure 6It can be seen that compared with the unregulated hydrogel, the hydrogel regulated by Na2SO4 has a higher lithium ion release efficiency. Moreover, after the hydrogel adsorbs lithium in a lithium solution with an initial concentration of 5 mg / L, the autonomous release efficiency of the adsorbed lithium ions is as high as 58%.

[0080] Example 10:

[0081] This embodiment relates to the gradient polyelectrolyte hydrogel before and after regulation by Na2SO4 to Li + / X (X represents other metal ions) selectivity test. The gradient polyelectrolyte hydrogel prepared in Example 1 before and after ion-specific effect regulation was cut into 10*10mm size and placed in a reverse electrodialysis device. The same salt solution of the same concentration was added to the chambers on both sides. After applying a voltage of -0.5~0.5V, the IV curve of the hydrogel for 0.1M LiCl, NaCl, MgCl2, and CaCl2 solutions was as follows: Figure 8-9 As shown, according to the IV curve and selectivity formula (where G represents ionic conductivity, c represents the corresponding ion concentration, and z represents the ion valence) The selectivity of the gradient polyelectrolyte hydrogel for lithium before and after the regulation of the ion-specific effect can be obtained as follows: Figure 10 As shown, from Figure 10 It can be seen that the gradient hydrogel regulated by Na2SO4 has a great influence on Li + / Na + 、Li + / K + 、Li + / Mg 2+ He Li + / Ca 2+ The selectivities of the hydrogel for Li + This indicates that the gradient hydrogel regulated by Na2SO4 prepared in Example 1 has high selectivity for the adsorption of lithium ions.

Claims

1. A method for preparing a gradient polyelectrolyte hydrogel with ion-specific effect regulation, characterized in that: The specific steps include: (1) dispersing methacrylic acid, acrylamide, a crosslinking agent, a photoinitiator, and a light absorber in ultrapure water and stirring to obtain a reaction mixture solution; (2) injecting the reaction mixture into a glass plate mold with a silicone gasket and irradiating with ultraviolet light for reaction; (3) The reacted material is immersed in a salt solution to undergo a gelation reaction, thereby obtaining a gradient polyelectrolyte hydrogel regulated by an ion-specific effect.

2. The method for preparing the ion-specific effect-regulated gradient polyelectrolyte hydrogel according to claim 1, characterized in that: The total molar concentration of methacrylic acid and acrylamide in the reaction mixture is 5-8 mol / L, and the molar concentration ratio is 1:(0.5-2); preferably, the total molar concentration of methacrylic acid and acrylamide in the reaction mixture is 5 mol / L, and the molar concentration ratio is 2:

1.

3. The method for preparing the ion-specific effect-regulated gradient polyelectrolyte hydrogel according to claim 1, characterized in that: In step (1), the cross-linking agent is N,N-methylenebis(acrylamide), and its concentration in the reaction mixture is 25-150 mM; the photoinitiator is α-ketoglutaric acid, and its concentration in the reaction mixture is 0.1-0.2 wt%; the concentration of the light absorber in the reaction mixture is 0.2-0.4 wt%; preferably, in the reaction mixture, the concentration of the cross-linking agent is 75 mM, and the concentration of the photoinitiator is 0.2 wt%.

4. The method for preparing the ion-specific effect-regulated gradient polyelectrolyte hydrogel according to claim 1, characterized in that: In step (2), the glass plate is soda-lime glass, and the thickness of the silicone gasket is 2 mm.

5. The method for preparing the ion-specific effect-regulated gradient polyelectrolyte hydrogel according to claim 1, characterized in that: In step (2), the reaction time is 4-5 h.

6. The method for preparing the ion-specific effect-regulated gradient polyelectrolyte hydrogel according to claim 1, characterized in that: The gelation reaction in step (3) is to place the reacted material in a salt solution and soak it for 24 hours; the salt solution is an aqueous solution of MgSO4, Na2SO4, NaCl or NaI, with a concentration of 0.5 to 2.5 mol / L.

7. A gradient polyelectrolyte hydrogel with ion-specific effects regulated by the preparation method according to any one of claims 1 to 6.

8. Use of the gradient polyelectrolyte hydrogel regulated by the ion-specific effect according to claim 7 in the extraction of lithium resources.

9. Use of the gradient polyelectrolyte hydrogel regulated by ion-specific effect according to claim 8 in extracting lithium resources, characterized in that: The application is to use a gradient polyelectrolyte hydrogel regulated by ion-specific effects in a lithium-containing solution, which can enable self-driven enrichment of lithium ions with high enrichment efficiency.

10. Use of the gradient polyelectrolyte hydrogel regulated by ion-specific effect according to claim 8 in adsorbing metal ions.

Images