PLGlu-SS-LITHIUM ION-SIEVE COMPOSITE, AND PREPARATION METHOD AND USE THEREOF

Abstract

Disclosed is a PLGlu-SS-lithium ion-sieve composite, preparation method and use thereof. The PLGlu-SS-lithium ion-sieve composite includes an H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve and poly--glutamic acid (-PGA) compounded with the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve, where a terminal amino group of the -PGA is linked to a disulfide bond-containing group. In the present disclosure, the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve is used as a support structure with sufficient strength support, high structural stability, and excellent cycling performance; the pores and surface of the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve both are bonded with PLGlu-SS. At a low pH, PLGlu-SS is protonated and folded to form-helix, and at a high pH, PLGlu-SS is deprotonated and extended. Thus, under alkaline adsorption and acidic desorption, a pore size of the composite can be adjusted to provide large adsorption capacity, high adsorption selectivity, and high adsorption efficiency. Therefore, the composite is an efficient lithium ion adsorption material with high adsorption capacity and high stability.

Claims

1. A PLGlu-SS-lithium ion-sieve composite, comprising an H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve and poly--glutamic acid (-PGA) compounded with the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve, wherein a terminal amino group of the -PGA is linked to a disulfide bond-containing group and a terminal carboxyl group of the -PGA is bonded with Ti and Mn in the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve.

2. The PLGlu-SS-lithium ion-sieve composite according to claim 1, wherein the disulfide bond-containing group is a group having COR.sup.1SSR.sup.2COOH, wherein R.sup.1 and R.sup.2 each are linear alkyl with 9 to 16 carbon atoms.

3. The PLGlu-SS-lithium ion-sieve composite according to claim 1, wherein a precursor of the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve is Li.sub.4MnTi.sub.4O.sub.12, and Li.sub.4MnTi.sub.4O.sub.12 is treated with an acid to obtain the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve.

4. The PLGlu-SS-lithium ion-sieve composite according to claim 1, wherein the -PGA has a molar molecular weight of 1,500 g/mol to 5,500 g/mol.

5. A preparation method of a PLGlu-SS-lithium ion-sieve composite, comprising the following steps: S1. preparation of a lithium ion-sieve: mixing a Mn.sup.2+-containing aqueous solution and a Ti.sup.4+-containing aqueous solution and adjusting a pH to 10 to 11 with ammonium hydroxide under stirring, adding hydrogen peroxide to oxidize Mn.sup.2+ into Mn.sup.4+, centrifuging a resulting reaction mixture, washing a resulting precipitate to obtain a solid, adding a LiOH solution to the solid, conducting hydrothermal crystallization to obtain a LiMnTi composite oxide, and cooling to 90 C. to 100 C.; and S2. preparation of the PLGlu-SS-lithium ion-sieve composite: adding PLGlu-SS to the LiMnTi composite oxide to allow a reaction, adding an excess amount of hydrochloric acid after the reaction is completed, stirring a resulting mixture to allow a further reaction for 12 h to 24 h, and subjecting a resulting reaction system to suction filtration to obtain the PLGlu-SS-lithium ion-sieve composite.

6. The preparation method of a PLGlu-SS-lithium ion-sieve composite according to claim 5, wherein a preparation method of the PLGlu-SS comprises the following steps: S21. adding mercaptoalkyl acid to a solution of hydrochloric acid in dimethyl sulfoxide to allow a reaction under stirring to obtain a disulfide bond-containing compound; S22. adding the disulfide bond-containing compound to dimethylformamide (DMF), adding o-(7-aza-1H-benzotriazol-1-yl)-N,N,N,N-tetramethyluronium hexafluorophosphate (HATU) and diisopropylethylamine (DIEA), then adding -PGA benzyl ester to allow an another reaction under stirring, and conducting recrystallization with methanol after the another reaction is completed to obtain a crystallization product; and S23. dissolving the crystallization product in a mixed solvent of dioxane and methanol, adding sodium hydroxide, stirring at room temperature for 1 h to 3 h, and dissolving a resulting precipitate in water and conducting ultrafiltration with an ultrafiltration membrane to obtain the PLGlu-SS.

7. The preparation method of a PLGlu-SS-lithium ion-sieve composite according to claim 6, wherein in step S21, the reaction is conducted for 12 h to 24 h; in step S22, a molar ratio of the disulfide bond-containing compound to HATU to DIEA is 1:(2-2.5):(2-3), a molar ratio of the -PGA benzyl ester to the disulfide bond-containing compound is 1:(1-2), and the another reaction is conducted at a temperature of 0 C. to 25 C. for 12 h to 36 h; and in step S23, a volume ratio of the dioxane to the methanol is (5-2):1, a concentration of the sodium hydroxide is 2 mol/L to 5 mol/L after the sodium hydroxide is added, and the ultrafiltration membrane has a molecular weight cut-off of lower than 10,000 daltons.

8. The preparation method of a PLGlu-SS-lithium ion-sieve composite according to claim 5, wherein Mn.sup.2+ is provided by one or more selected from the group consisting of manganese sulfate, manganese oxalate, and manganese acetate, and Ti.sup.4+ is provided by one selected from the group consisting of titanium tetrachloride and titanium sulfate.

9. The preparation method of a PLGlu-SS-lithium ion-sieve composite according to claim 6, wherein Mn.sup.2+ is provided by one or more selected from the group consisting of manganese sulfate, manganese oxalate, and manganese acetate, and Ti.sup.4+ is provided by one selected from the group consisting of titanium tetrachloride and titanium sulfate.

10. The preparation method of a PLGlu-SS-lithium ion-sieve composite according to claim 7, wherein Mn.sup.2+ is provided by one or more selected from the group consisting of manganese sulfate, manganese oxalate, and manganese acetate, and Ti.sup.4+ is provided by one selected from the group consisting of titanium tetrachloride and titanium sulfate.

11. The preparation method of a PLGlu-SS-lithium ion-sieve composite according to claim 5, wherein a molar ratio of Mn.sup.2+ to Ti.sup.4+ is 1:(4-4.5), a molar ratio of LiOH to Ti.sup.4+ is (1-1.2):1, and the hydrothermal crystallization is conducted at a temperature of 750 C. to 850 C.

12. The preparation method of a PLGlu-SS-lithium ion-sieve composite according to claim 6, wherein a molar ratio of Mn.sup.2+ to Ti.sup.4+ is 1:(4-4.5), a molar ratio of LiOH to Ti.sup.4+ is (1-1.2):1, and the hydrothermal crystallization is conducted at a temperature of 750 C. to 850 C.

13. The preparation method of a PLGlu-SS-lithium ion-sieve composite according to claim 7, wherein a molar ratio of Mn.sup.2+ to Ti.sup.4+ is 1:(4-4.5), a molar ratio of LiOH to Ti.sup.4+ is (1-1.2):1, and the hydrothermal crystallization is conducted at a temperature of 750 C. to 850 C.

14. Use of a PLGlu-SS-lithium ion-sieve composite in lithium extraction from a salt lake.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 is a scanning electron microscopy (SEM) image of a H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve in Comparative Example 1;

[0035] FIG. 2 is an SEM image of a PLGlu-SS-lithium ion-sieve in Example 4;

[0036] FIG. 3 shows a pore size distribution of the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve in Comparative Example 1;

[0037] FIG. 4 shows a pore size distribution of the PLGlu-SS-lithium ion-sieve in Example 4;

[0038] FIG. 5 shows a change of an adsorption amount over time of each of the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve and the PLGlu-SS-lithium ion-sieve in a solution with a Li.sup.+ concentration of 20 mg/L;

[0039] FIG. 6 shows a change of an adsorption amount over time of each of the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve and the PLGlu-SS-lithium ion-sieve in a solution with a Li.sup.+ concentration of 5,000 mg/L; and

[0040] FIG. 7 shows a change of lithium ion desorption of the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve and the PLGlu-SS-lithium ion-sieve over time.

DETAILED DESCRIPTION

[0041] The technical solutions in the present disclosure will be clearly and completely described below in conjunction with specific examples. Apparently, the described examples are some rather than all of the examples of the present disclosure. All other examples obtained by a person of ordinary skill in the art based on the examples of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.

[0042] The existing lithium ion-sieves mainly includes manganese-based lithium ion-sieves and titanium-based lithium ion-sieves. Manganese will be partly dissolved when a manganese-based lithium ion-sieve is subjected to lithium elution with an acid, which weakens the structural stability and adsorption performance of the manganese-based lithium ion-sieve and shortens the cycling life of the manganese-based lithium ion-sieve. The titanium-based lithium ion-sieves have a relatively low dissolution loss and exhibit better chemical performance and selective adsorption for Li.sup.+ than the manganese-based lithium ion-sieves. However, a powdery titanium-based lithium ion-sieve has large Li.sup.+ mass transfer diffusion resistance and low active ingredient utilization efficiency. Therefore, in the present disclosure, H.sub.3LiMnTi.sub.4O.sub.12 is used as a main body of an ion sieve, and the ion sieve is modified with PLGlu-SS to improve the adsorption performance of the ion sieve.

[0043] A PLGlu-SS-lithium ion-sieve composite is provided, including an H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve and -PGA compounded with the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve, wherein a terminal amino group of the -PGA is linked to a disulfide bond-containing group and a terminal carboxyl group of the -PGA is bonded with Ti and Mn in the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve.

[0044] The H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve is used as a support structure, which has sufficient strength support, high structural stability, and excellent cycling performance; and the pores and surface of the lithium ion-sieve both are bonded with PLGlu-SS. At a low pH, PLGlu-SS is protonated and folded to form-helix to increase a pore size, such that H.sup.+ can smoothly contact Li.sup.+ to exchange with Li.sup.+ and Li.sup.+ can smoothly flow out of the pores, thereby achieving desorption. At a high pH, PLGlu-SS is deprotonated and extended. Thus, under alkaline adsorption and acidic desorption, a pore size of the composite can be adjusted to provide large adsorption capacity, high adsorption selectivity, and high adsorption efficiency.

[0045] In an embodiment, the disulfide bond-containing group is a group with COR.sup.1SSR.sup.2COOH, wherein R.sup.1 and R.sup.2 each are linear alkyl with 9 to 16 carbon atoms.

[0046] The folding and extension of the disulfide bond-containing group change the surface and pore structure of the lithium ion-sieve. Glutamic acid has an ionic coupling effect and can capture ions to the surface of the lithium ion-sieve; and the disulfide bond-containing group in the pores can extend during alkaline adsorption to reduce a pore size of the pores, such that Li.sup.+ with a small ion radius can further move to adsorption sites in the pores. Thus, a volume after the disulfide bond-containing group is extended and folded is a main factor affecting the lithium ion adsorption. Therefore, volumes of R.sup.1 and R.sup.2 (linear alkyls with 9 to 16 carbon atoms) during the extension and folding allow the smooth passage of Li.sup.+, thereby improving the adsorption and desorption effect.

[0047] In an embodiment, a precursor of the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve is Li.sub.4MnTi.sub.4O.sub.12, and Li.sub.4MnTi.sub.4O.sub.12 is treated with an acid to obtain the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve.

[0048] In an embodiment, the -PGA has a molar molecular weight of 1,500 g/mol to 5,500 g/mol.

[0049] To facilitate the binding in the pores, the molecular weight of -PGA should not be too large and thus is limited to 5,500 g/mol or lower; and to ensure the structural stability, the molecular weight of -PGA is limited to 1,500 g/mol or higher to prevent the structure from being destructed during adsorption and elution.

[0050] The present disclosure also provides a preparation method of a PLGlu-SS-lithium ion-sieve composite, including the following steps: [0051] S1. preparation of a lithium ion-sieve: mixing a Mn.sup.2+-containing aqueous solution and a Ti.sup.4+-containing aqueous solution and adjusting a pH to 10 to 11 with ammonium hydroxide under stirring, adding hydrogen peroxide to oxidize Mn.sup.2+ into Mn.sup.4+, centrifuging a resulting reaction mixture, washing a resulting precipitate to obtain a solid, adding a LiOH solution to the solid, conducting hydrothermal crystallization to obtain a LiMnTi composite oxide, and cooling to 90 C. to 100 C.; and [0052] S2. preparation of the PLGlu-SS-lithium ion-sieve composite:

[0053] adding the PLGlu-SS to the LiMnTi composite oxide to allow a reaction, adding an excess amount of hydrochloric acid after the reaction is completed, stirring a resulting mixture to allow a further reaction for 12 h to 24 h, and subjecting a resulting reaction system to suction filtration to obtain the PLGlu-SS-lithium ion-sieve composite.

[0054] PLGlu-SS is a compound obtained by linking a disulfide bond-containing group to -PGA. The disulfide bond-containing group is a group with COR.sup.1SSR.sup.2COOH, wherein R.sup.1 and R.sup.2 both are linear alkyl with 9 to 16 carbon atoms, and a carbonyl group of a disulfide bond and a terminal amino group of -PGA are linked to form PLGlu-SS.

[0055] In an embodiment, a preparation method of the PLGlu-SS includes the following steps: [0056] S21. adding mercaptoalkyl acid to a solution of hydrochloric acid in dimethyl sulfoxide to allow a reaction under stirring to obtain a disulfide bond-containing compound; [0057] S22. adding the disulfide bond-containing compound to DMF, adding HATU and DIEA, then adding -PGA benzyl ester to allow an another reaction under stirring, and conducting recrystallization with methanol after the another reaction is completed to obtain a crystallization product; and [0058] S23. dissolving the crystallization product in a mixed solvent of dioxane and methanol, adding sodium hydroxide, stirring at room temperature for 1 h to 3 h, and dissolving a resulting precipitate in water and conducting ultrafiltration with an ultrafiltration membrane to obtain the PLGlu-SS.

[0059] In an embodiment, in step S21, the reaction is conducted for 12 h to 24 h;

[0060] in step S22, a molar ratio of the disulfide bond-containing compound to HATU to DIEA is 1:(2-2.5):(2-3), a molar ratio of the -PGA benzyl ester to the disulfide bond-containing compound is 1:(1-2), and the another reaction is conducted at a temperature of 0 C. to 25 C. for 12 h to 36 h; and

[0061] in step S23, a volume ratio of the dioxane to the methanol is (5-2):1, a concentration of the sodium hydroxide after the sodium hydroxide is added is 2 mol/L to 5 mol/L, and the ultrafiltration membrane has a molecular weight cut-off of lower than 10,000 daltons.

[0062] In an embodiment, Mn.sup.2+ is provided by one or more selected from the group consisting of manganese sulfate, manganese oxalate, and manganese acetate, and Ti.sup.4+ is provided by one selected from the group consisting of titanium tetrachloride and titanium sulfate.

[0063] In an embodiment, a molar ratio of Mn.sup.2+ to Ti.sup.4+ is 1:(4-4.5), a molar ratio of LiOH to Ti.sup.4+ is (1-1.2):1, and the hydrothermal crystallization is conducted at a temperature of 750 C. to 850 C.

[0064] The PLGlu-SS-lithium ion-sieve composite of the present disclosure can be used in lithium extraction from a salt lake.

Example 1

[0065] Preparation of PLGlu-SS

[0066] 11-Mercaptoundecanoic acid was added to a dimethyl sulfoxide solution with hydrochloric acid at a concentration of 1 mol/L, and a resulting mixture was stirred to allow a reaction for 16 h to produce a disulfide bond-containing compound; a large amount of water was added for precipitation, and a resulting precipitate was collected to obtain a disulfide bond-containing compound; 2 mmol of the disulfide bond-containing compound was added to DMF, then 4.4 mmol of HATU and 5 mmol of DIEA were added, then 3 mmol of -PGA benzyl ester was added to allow a reaction for 24 h under stirring at 15 C.; after the reaction was completed, recrystallization was conducted with methanol; a crystallization product was dissolved in a mixed solvent of 6 mL of dioxane and 3 mL of methanol, sodium hydroxide was added until its concentration was 3 mol/L, and a resulting reaction mixture was stirred at room temperature for 2 h; and another resulting precipitate was collected and dissolved in water, a resulting solution was subjected to ultrafiltration by an ultrafiltration membrane with a molecular weight cut-off of 10,000, and a concentrate was lyophilized to obtain the PLGlu-SS.

Example 2

[0067] Preparation of PLGlu-SS

[0068] 16-Mercaptohexadecanoic acid was added to a dimethyl sulfoxide solution with hydrochloric acid at a concentration of 1 mol/L, and a resulting mixture was stirred to allow a reaction for 24 h to produce a disulfide bond-containing compound; a large amount of water was added for precipitation, and a resulting precipitate was collected to obtain a disulfide bond-containing compound; 2 mmol of the disulfide bond-containing compound was added to DMF, then 4 mmol of HATU and 6 mmol of DIEA were added, then 2 mmol of -PGA benzyl ester was added to allow a reaction for 12 h under stirring at 25 C.; after the reaction was completed, recrystallization was conducted with methanol; a crystallization product was dissolved in a mixed solvent of 10 mL of dioxane and 2 mL of methanol, sodium hydroxide was added until its concentration was 2 mol/L, and a resulting reaction mixture was stirred at room temperature for 3 h; and another resulting precipitate was collected and dissolved in water, a resulting solution was subjected to ultrafiltration by an ultrafiltration membrane with a molecular weight cut-off of 10,000, and a concentrate was lyophilized to obtain the PLGlu-SS.

Example 3

[0069] Preparation of PLGlu-SS

[0070] 9-Mercaptononanoic acid was added to a dimethyl sulfoxide solution with hydrochloric acid at a concentration of 1 mol/L, and a resulting mixture was stirred to allow a reaction for 12 h to produce a disulfide bond-containing compound; a large amount of water was added for precipitation, and a resulting precipitate was collected to obtain a disulfide bond-containing compound; 2 mmol of the disulfide bond-containing compound was added to DMF, then 5 mmol of HATU and 4 mmol of DIEA were added, then 4 mmol of -PGA benzyl ester was added to allow a reaction for 36 h under stirring at 0 C.; after the reaction was completed, recrystallization was conducted with methanol; a crystallization product was dissolved in a mixed solvent of 7 mL of dioxane and 2 mL of methanol, sodium hydroxide was added until its concentration was 5 mol/L, and a resulting reaction mixture was stirred at room temperature for 1 h; and another resulting precipitate was collected and dissolved in water, a resulting solution was subjected to ultrafiltration by an ultrafiltration membrane with a molecular weight cut-off of 10,000, and a concentrate was lyophilized to obtain the PLGlu-SS.

Example 4

[0071] Preparation of a PLGlu-SS-Lithium Ion-Sieve Composite:

[0072] Preparation of a lithium ion-sieve: A MnSO.sub.4 aqueous solution and a Ti(SO.sub.4).sub.2 aqueous solution were mixed in a molar ratio of Mn.sup.2+ to Ti.sup.4+ of 1:4, a pH was adjusted to 10 to 11 with ammonium hydroxide under stirring, hydrogen peroxide was added to oxidize Mn.sup.2+ into Mn.sup.4+, a resulting solid was collected through centrifugation and washed with water until there was no sulfate, the solid was added to a LiOH solution in which LiOH was contained in a same amount as Ti(SO.sub.4).sub.2, hydrothermal crystallization was conducted at 800 C. to produce a LiMnTi composite oxide, and a resulting reaction system was cooled to 95 C. Preparation of the PLGlu-SS-lithium ion-sieve composite: The PLGlu-SS prepared in Example 1 was added to the LiMnTi composite oxide to allow a reaction at 95 C.; after the reaction was completed, a resulting reaction mixture was cooled to room temperature, an excess amount of 2 mol/L hydrochloric acid was added to allow another reaction for 18 h under stirring, suction filtration was conducted to give a filter residue after the another reaction was completed, the filter residue was added to 2 mol/L hydrochloric acid again, and a resulting mixture was stirred at room temperature for 18 h and then subjected to suction filtration to obtain the PLGlu-SS-lithium ion-sieve composite.

Example 5

[0073] Preparation of a PLGlu-SS-Lithium Ion-Sieve Composite:

[0074] Preparation of a lithium ion-sieve: A manganese oxalate aqueous solution and a titanium tetrachloride aqueous solution were mixed in a molar ratio of Mn.sup.2+ to Ti.sup.4+ of 1:4.2, a pH was adjusted to 10 to 11 with ammonium hydroxide under stirring, hydrogen peroxide was added to oxidize Mn.sup.2+ into Mn.sup.4+, a resulting solid was collected through centrifugation and washed with water, and the solid was added to a LiOH solution in which LiOH was contained in an amount of 1.1 times the amount of titanium tetrachloride, hydrothermal crystallization was conducted at 750 C. to produce a LiMnTi composite oxide, and a resulting reaction system was cooled to 100 C. Preparation of the PLGlu-SS-lithium ion-sieve composite: The PLGlu-SS prepared in Example 2 was added to the LiMnTi composite oxide to allow a reaction at 100 C.; after the reaction was completed, a resulting reaction mixture was cooled to room temperature, an excess amount of 2 mol/L hydrochloric acid was added to allow another reaction for 12 h under stirring, suction filtration was conducted to give a filter residue after the another reaction was completed, the filter residue was added to 2 mol/L hydrochloric acid again, and a resulting mixture was stirred at room temperature for 24 h and then subjected to suction filtration to obtain the PLGlu-SS-lithium ion-sieve composite.

Example 6

[0075] Preparation of a PLGlu-SS-Lithium Ion-Sieve Composite:

[0076] Preparation of a lithium ion-sieve: A manganese acetate aqueous solution and a Ti(SO.sub.4).sub.2 aqueous solution were mixed in a molar ratio of Mn.sup.2+ to Ti.sup.4+ of 1:4.5, a pH was adjusted to 10 to 11 with ammonium hydroxide under stirring, hydrogen peroxide was added to oxidize Mn.sup.2+ into Mn.sup.4+, a resulting solid was collected through centrifugation and washed with water, the solid was added to a LiOH solution in which LiOH was contained in an amount of 1.2 times the amount of Ti(SO.sub.4).sub.2, hydrothermal crystallization was conducted at 850 C. to produce a LiMnTi composite oxide, and a resulting reaction system was cooled to 90 C. Preparation of the PLGlu-SS-lithium ion-sieve composite: The PLGlu-SS prepared in Example 3 was added to the LiMnTi composite oxide to allow a reaction at 90 C.; after the reaction was completed, a resulting reaction mixture was cooled to room temperature, an excess amount of 2 mol/L hydrochloric acid was added, to allow another reaction for 24 h under stirring, suction filtration was conducted to give a filter residue after the another reaction was completed, the filter residue was added to 2 mol/L hydrochloric acid again, and a resulting mixture was stirred at room temperature for 24 h and then subjected to suction filtration to obtain the PLGlu-SS-lithium ion-sieve composite.

Comparative Example 1

[0077] This comparative example was different from Example 4 in that the LiMnTi composite oxide was directly mixed with the 2 mol/L hydrochloric acid without the addition of the PLGlu-SS in Example 1, and a resulting mixture was stirred to allow a reaction for 18 h and then subjected to suction filtration to obtain an H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve.

Test Example

[0078] SEM characterization: The H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve in Comparative Example 1 and the PLGlu-SS-lithium ion-sieve in Example 4 each were subjected to SEM characterization, and resulting SEM images were shown in FIG. 1 and FIG. 2, respectively.

[0079] The H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve in FIG. 1 has a rough surface, many pores, and a block structure as a whole. It can be seen from FIG. 2 that, after PLGlu-SS is bonded to the lithium ion-sieve, a surface of the lithium ion-sieve is covered with a rough material layer, the block structure becomes rounded, and block layers are linked holistically. Therefore, it can be speculated that the bonding of PLGlu-SS to the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve can greatly improve the surface area and the pore structure.

[0080] Pore size analysis: The H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve in Comparative Example 1 and the PLGlu-SS-lithium ion-sieve in Example 4 each were subjected to a specific surface area test for pore size analysis, where a pore size distribution of the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve in Comparative Example 1 was shown in FIG. 3 and a pore size distribution of the PLGlu-SS-lithium ion-sieve in Example 4 was shown in FIG. 4.

[0081] It can be seen from FIG. 3 that the pore size distribution of the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve is mainly concentrated at 1.7 nm and 2.5 nm. It can be seen from FIG. 4 that the pore size distribution of the PLGlu-SS-lithium ion-sieve obtained through PLGlu-SS bonding at 2.5 nm and 1.7 nm is reduced, and the pore size distribution is concentrated at 1.25 nm, indicating that PLGlu-SS successfully modifies the pores of the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve.

Experimental Example

[0082] Lithium Ion Adsorption Experiment:

[0083] Solutions with Li.sup.+ concentrations of 20 mg/L and 5,000 mg/L respectively were prepared, and a pH of each of the solutions was adjusted with KOH to 11; and 2 g of each of the PLGlu-SS-lithium ion-sieve in Example 1 and the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve in Comparative Example 1 was taken and added to the solutions with Li.sup.+ concentrations of 20 mg/L and 5,000 mg/L, respectively, and resulting mixtures were magnetically stirred for 24 h at room temperature to allow adsorption. A Li.sup.+ concentration in each solution was determined every 1 h, and an adsorption amount of each of the PLGlu-SS-lithium ion-sieve in Example 1 and the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve in Comparative Example 1 in the solutions was calculated. Results were shown in FIG. 5 and FIG. 6.

[0084] As shown in FIG. 5, in the case where the PLGlu-SS-lithium ion-sieve is used for adsorption in the solution with a Li.sup.+ concentration of 20 mg/L, the adsorption saturation is achieved within 7 h to 8 h, and an adsorption amount after 8 h is calculated to be 8.123 mg by measuring a residual Li.sup.+ concentration in the solution. Thus, an adsorption capacity of the PLGlu-SS-lithium ion-sieve in the solution with a Li.sup.+ concentration of 20 mg/L is 4.0615 mg/g. In contrast, for the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve, the adsorption saturation is approached after 15 h, and an adsorption amount after 15 his 7.658 mg. Thus, an adsorption capacity of the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve in the solution with a Li.sup.+ concentration of 20 mg/L is 3.829 mg/g. Apparently, an adsorption rate of the PLGlu-SS-lithium ion-sieve is higher than an adsorption rate of the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve. Similarly, in the solution with a Li.sup.+ concentration of 50,000 mg/L, the PLGlu-SS-lithium ion-sieve can reach adsorption saturation after 4.5 h, with an adsorption capacity of 126.563 mg/g; and the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve takes 7.5 h or more to reach adsorption saturation and has an adsorption capacity of 118.237 mg/g. Therefore, the PLGlu-SS-lithium ion-sieve of the present disclosure can significantly increase the adsorption rate while increasing the adsorption capacity.

[0085] Lithium Ion Desorption Experiment:

[0086] In the lithium ion adsorption experiment, a solution with a Li.sup.+ concentration of 50,000 mg/L was subjected to adsorption with the PLGlu-SS-lithium ion-sieve for 5 h and the same solution was subjected to adsorption with the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve for 10 h, resulting solutions were centrifuged, resulting supernatants were tested for a lithium ion concentration, and adsorption amounts of the two lithium ion-sieves were calculated to 252.615 mg and 238.442 mg, respectively; and then the two lithium ion-sieves each were added to 2 L of a 2 mol/L hydrochloric acid solution, and resulting mixtures were stirred at room temperature for 12 h, during which a lithium ion concentration in each of the solutions was detected every half hour and a desorption amount was calculated. Results were shown in FIG. 7.

[0087] It can be seen from FIG. 7 that, when the PLGlu-SS-lithium ion-sieve in a saturated adsorption state is subjected to desorption in the 2 mol/L hydrochloric acid solution, a desorption amount can reach 98.41% after about 3 h; and when the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve in a saturated adsorption state is subjected to desorption in the 2 mol/L hydrochloric acid solution, a desorption amount is merely 72.40% after 3 h and 93.66% after 7 h, and can reach 98.13% after 12 h. Therefore, it can be known that, when the PLGlu-SS-lithium ion-sieve is subjected to desorption in the 2 mol/L hydrochloric acid solution, the nearly-complete desorption can be achieved in a relatively short period of time, which is uncomparable for the H.sub.3LiMnTi.sub.4O.sub.12 lithium ion-sieve.

[0088] PLGlu-SS-Lithium Ion-Sieve Recycling Experiment:

[0089] The PLGlu-SS-lithium ion-sieve undergone adsorption and desorption was subjected to adsorption in a solution with a Li.sup.+ concentration of 50,000 mg/L for 5 h and then to desorption in a 2 mol/L hydrochloric acid solution for 5 h, which was repeated five times. An adsorption amount and a desorption amount each time were calculated, and results were shown in Table 1.

TABLE-US-00001 TABLE 1 Adsorption-desorption results of PLGlu-SS-lithium ion-sieve Adsorption Desorption amount (mg) rate (%) Second adsorption-desorption 249.895 99.22 Third adsorption-desorption 250.089 99.32 Fourth adsorption-desorption 249.957. 99.15 Fifth adsorption-desorption 249.735 99.05 Sixth adsorption-desorption 248.568 98.89

[0090] It can be seen from Table 1 that, in the six adsorption-desorption cycles, the adsorption amount tends to decrease, but by a small amount, the desorption rate is still high and can reach about 99%, and the adsorption-desorption cycle is short. Therefore, the PLGlu-SS-lithium ion-sieve has excellent stability and reusability.

[0091] In summary, the PLGlu-SS-lithium ion-sieve composite of the present disclosure has sufficient strength support, high structural stability, and excellent cycling performance. Thus, under alkaline adsorption and acidic desorption, a pore size of the composite can be adjusted to provide large adsorption capacity, high adsorption selectivity, and high adsorption efficiency. Therefore, the composite is an efficient lithium ion adsorption material with high adsorption capacity and high stability.

[0092] The above examples are merely preferred implementations of the present disclosure, and are not intended to limit the protection scope of the present disclosure. Any nonessential modifications and substitutions made by those skilled in the art on the basis of the present disclosure fall within the protection scope of the present disclosure.