A gradient porous lithium ion sieve nanofiber aerogel and its preparation method and application

Abstract

The present invention provides a gradient porous lithium ion sieve nanofiber aerogel and its preparation method and application, belonging to the field of nanofiber material technology. The preparation method is: dissolving lithium ion sieve and organic polymer in a solvent to obtain a spinning solution, and then electrospinning the spinning solution to obtain a lithium ion sieve precursor nanofiber membrane; calcining the lithium ion sieve precursor nanofiber membrane at high temperature to obtain a pure lithium ion sieve nanofiber membrane; dispersing the pure lithium ion sieve nanofiber membrane into a solution system containing a cross-linking agent and a catalyst, and then freeze-drying and high-temperature treating the obtained lithium ion sieve nanofiber dispersion in sequence to obtain the target product. The lithium ion sieve nanofiber aerogel material obtained by the preparation method provided by the present invention has a lithium ion sieve content of 100% and is in a uniform nanofiber form, and has the characteristics of high lithium ion sieve content, fully open adsorption sites, high porosity, underwater stable superelasticity, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiber materials, and in particular to a gradient porous lithium ion sieve nanofiber aerogel and a preparation method and application thereof. Background Art

[0002] With the rapid development of new energy vehicles and energy storage technologies, lithium plays a crucial role in the field of new energy materials, resulting in a surge in demand for lithium salts and a supply-demand gap. Therefore, the development of low-cost, high-efficiency, and recyclable lithium extraction technologies has attracted widespread attention. Selective adsorption of lithium ions from salt lake brine is a simple, efficient, and low-pollution lithium extraction technology. Lithium ion sieves, due to their highly selective adsorption of lithium ions, have become a research hotspot for lithium extraction from salt lake brines. To address the problems of lithium ion sieve powder being difficult to recycle and prone to water pollution in practical applications, existing lithium adsorption material preparation technologies primarily involve physically blending lithium ion sieve powder with organic polymers. Macroscopically continuous lithium ion sieve adsorption materials are prepared through methods such as sol-gel, electrospinning, granulation, foaming, and coating. For example, Chinese invention patent CN115874356 A discloses a lithium ion sieve nanofiber felt and its preparation method. These materials are prepared by blending lithium ion sieve powder with a polymer in a specific solvent to form a spinning solution, which is then electrospun to produce the lithium ion sieve nanofiber felt for lithium ion adsorption. However, the lithium adsorption material obtained by this technical means has problems such as low lithium ion sieve loading and high radial stacking degree of fibers, which makes it difficult for its lithium adsorption capacity and permeation flux to meet the actual application requirements. For example, the preparation method of a monolithic lithium ion sieve with a hierarchical pore structure described in Chinese invention patent CN106732441 B, which dissolves lithium ion sieve powder and polyacrylonitrile in DMSO solvent, and then obtains a lithium ion sieve composite material with a hierarchical pore structure by sol-gel and freeze-drying methods. However, the lithium ion sieve adsorption material prepared by this technology has problems such as low lithium ion sieve loading, active sites are easily covered and closed by polyacrylonitrile, and the overall pore structure of the material is unevenly distributed, which seriously affects its actual application performance in the field of lithium ion adsorption. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a gradient porous lithium ion sieve nanofiber aerogel and its preparation method and application. The preparation method provided by the present invention can obtain a macroscopically continuous, gradient porous pure lithium ion sieve nanofiber aerogel material, which has no organic polymer support in its structure, and the lithium ion sieve content reaches 100% and is in a uniform nanofiber form. It has the characteristics of high lithium ion sieve content, fully open adsorption sites, high porosity, underwater stable superelasticity, etc., which can ensure that the material has an adsorption capacity equivalent to its powder state and a permeation flux and adsorption rate better than its powder state, so as to achieve its special application in the field of lithium extraction from salt lakes and seawater.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] One of the technical solutions of the present invention is a method for preparing a gradient porous lithium ion sieve nanofiber aerogel, comprising the following steps:

[0006] The lithium ion sieve and the organic polymer are dissolved in a solvent to obtain a spinning solution, and then the spinning solution is electrospinned to obtain a lithium ion sieve precursor nanofiber membrane;

[0007] calcining the lithium ion sieve precursor nanofiber membrane at high temperature to obtain a pure lithium ion sieve nanofiber membrane;

[0008] The pure lithium ion sieve nanofiber membrane is dispersed in a solution system containing a crosslinking agent and a catalyst, and then the obtained lithium ion sieve nanofiber dispersion is freeze-dried and high-temperature treated in sequence to obtain the gradient porous lithium ion sieve nanofiber aerogel.

[0009] The second technical solution of the present invention is a gradient porous lithium ion sieve nanofiber aerogel prepared by the above preparation method.

[0010] The third technical solution of the present invention is an application of the above-mentioned gradient porous lithium ion sieve nanofiber aerogel in the selective extraction of lithium from salt lakes and seawater with a high magnesium-to-lithium ratio.

[0011] The present invention discloses the following technical effects:

[0012] The preparation method of the gradient porous lithium ion sieve nanofiber aerogel provided by the present invention can ensure that the lithium ion sieve content in the final prepared aerogel reaches 100% and has a uniform nanofiber morphology. This not only ensures the high specific surface area and adsorption sites of the lithium ion sieve itself, but also gives the material macroscopic continuity and gradient pore uniformity.

[0013] The open micropores in the lithium ion sieve nanofiber aerogel provided by the present invention and the macropores produced by the entanglement of nanofibers can effectively reduce the mass transfer resistance of water flow during the adsorption process. The mesopores on the surface of the lithium ion sieve nanofiber can ensure the high specific surface area and a large number of adsorption sites of the material, achieving the requirements of high throughput, high adsorption rate and high adsorption capacity that need to be met in the lithium extraction technology of salt lakes and seawater.

[0014] The lithium ion sieve nanofiber aerogel provided by the present invention is a three-dimensional network composed of flexible nanofibers intertwined and bonded with each other, which makes the material have excellent stability and flexibility underwater, meeting the requirements for material stability and durability in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 This is a flow chart for preparing the gradient porous lithium ion sieve nanofiber aerogel of the present invention;

[0017] Figure 2 This is the lithium ion adsorption isotherm of the lithium ion sieve nanofiber aerogel prepared in Example 1 of the present invention;

[0018] Figure 3 This is an SEM image of the pore structure of the lithium ion sieve nanofiber aerogel prepared in Example 1 of the present invention;

[0019] Figure 4 This is the underwater compression-recovery curve of the lithium ion sieve nanofiber aerogel prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0020] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0021] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0022] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0023] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0024] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0025] The present invention provides a method for preparing a gradient porous lithium ion sieve nanofiber aerogel, comprising the following steps:

[0026] The lithium ion sieve and the organic polymer are dissolved in a solvent to obtain a spinning solution, and then the spinning solution is electrospinned to obtain a lithium ion sieve precursor nanofiber membrane;

[0027] calcining the lithium ion sieve precursor nanofiber membrane at high temperature to obtain a pure lithium ion sieve nanofiber membrane;

[0028] The pure lithium ion sieve nanofiber membrane is dispersed in a solution system containing a crosslinking agent and a catalyst, and then the obtained lithium ion sieve nanofiber dispersion is freeze-dried and high-temperature treated in sequence to obtain the gradient porous lithium ion sieve nanofiber aerogel.

[0029] The present invention first dissolves a lithium ion sieve and an organic polymer in a solvent to obtain a spinning solution, and then electrostatically spins the spinning solution to obtain a lithium ion sieve precursor nanofiber membrane.

[0030] In some embodiments of the present invention, the lithium ion sieve is H 1.6 Mn 1.6 O4, HMn2O4, H2MnO3, H2TiO3, H4Ti5O 12 and at least one of HCl·2Al(OH)3; the mass ratio of the lithium ion sieve to the organic polymer is 1:(0.5-2).

[0031] In some embodiments of the present invention, the organic polymer is at least one of polyacrylonitrile, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, nylon 6 and polyvinylidene fluoride; and the concentration of the organic polymer in the spinning solution is 4-15 wt%.

[0032] In some embodiments of the present invention, the solvent is at least one of deionized water, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), dimethylacetamide (DMAc) and formic acid.

[0033] In some embodiments of the present invention, after the lithium ion sieve and the organic polymer are dissolved in a solvent, an ultrasonic step is further included; the ultrasonic frequency is 15-50 Hz, the temperature is 25° C., and the time is 10-60 min.

[0034] In some embodiments of the present invention, the process parameters of the electrospinning are: voltage 15-30kV, liquid supply rate 0.2-5.0mL / min, receiving distance 10-40cm, drum speed 30-80r / min, spinning temperature 20-28°C, humidity 20-80%, and the material for receiving the fiber membrane is oil-absorbing paper, tin foil, aluminum foil or non-woven fabric.

[0035] In some embodiments of the present invention, after the electrospinning is completed, the step of drying the obtained lithium ion sieve precursor nanofiber membrane is further included; the drying is vacuum drying; the drying temperature is 80° C. and the drying time is 12 hours.

[0036] After obtaining the lithium ion sieve precursor nanofiber membrane, the present invention calcines the obtained lithium ion sieve precursor nanofiber membrane at high temperature to obtain a highly crystalline and flexible pure lithium ion sieve nanofiber membrane.

[0037] In some embodiments of the present invention, the high-temperature calcination is carried out at a temperature of 400-800° C. and for a time of 2-10 h.

[0038] In the present invention, when the calcination temperature and time are lower than the above ranges, the crystallinity of the lithium ion sieve precursor will be low and the organic polymer will be incompletely removed; when the calcination temperature is higher than the above range, it is easy to cause the organic polymer to melt and remove too quickly, causing the nanofiber structure of the lithium ion sieve precursor to collapse; both of the above situations will have an adverse effect on the lithium adsorption performance and mechanical properties of the final material.

[0039] After obtaining a pure lithium ion sieve nanofiber membrane, the present invention disperses the obtained pure lithium ion sieve nanofiber membrane into a solution system containing a crosslinking agent and a catalyst. The obtained lithium ion sieve nanofiber dispersion is then freeze-dried and subjected to high-temperature treatment in sequence to obtain the gradient porous lithium ion sieve nanofiber aerogel. The present invention obtains the lithium ion sieve nanofiber aerogel by freeze-drying the lithium ion sieve nanofiber dispersion, and then subjecting the lithium ion sieve nanofiber aerogel to a high-temperature treatment for a crosslinking reaction to obtain a crosslinked lithium ion sieve nanofiber aerogel (i.e., a gradient porous lithium ion sieve nanofiber aerogel).

[0040] In some embodiments of the present invention, the present invention first cuts the pure lithium ion sieve nanofiber membrane into pieces, and then disperses the pieces into a solution system containing a cross-linking agent and a catalyst.

[0041] In some embodiments of the present invention, the dispersion method is high-speed shear dispersion; the conditions of the high-speed shear dispersion are: rotation speed 5000-10000 rpm, time 1-10 min.

[0042] In some embodiments of the present invention, the crosslinking agent is at least one of trimethoxymethylsilane, (3-methoxypropyl)trimethoxysilane and 3-aminopropyltriethoxysilane; the concentration of the crosslinking agent in the lithium ion sieve nanofiber dispersion is 0.1-0.5wt%;

[0043] The catalyst is oxalic acid; the concentration of the catalyst in the lithium ion sieve nanofiber dispersion is 0-0.005wt%, preferably 0.002-0.004wt%;

[0044] In some embodiments of the present invention, the solvent in the solution system containing the cross-linking agent and the catalyst is at least one of water, isopropyl alcohol, acetone and tert-butyl alcohol.

[0045] In some embodiments, the concentration of the lithium ion sieve nanofibers in the lithium ion sieve nanofiber dispersion is 5-15 wt %; the diameter of the lithium ion sieve nanofibers is 200-950 nm, and the length is 20-500 μm.

[0046] In the present invention, if the concentration of lithium ion sieve nanofibers is higher than the above parameters, the following two consequences will occur: (1) the high-concentration nanofibers will be too tightly entangled to form a uniform and stable dispersion, resulting in an uneven nanofiber structure and poor mechanical properties in the aerogel; (2) the fibers will be excessively entangled in the final aerogel structure, severely reducing the porosity of the aerogel and blocking some adsorption sites. If the concentration of lithium ion sieve nanofibers is lower than the above parameters, the nanofibers will be insufficiently entangled in the dispersion, resulting in poor mechanical properties of the aerogel or collapse of the bulk network during the drying process.

[0047] In some embodiments of the present invention, the freeze-drying parameters are: freezing temperature of -197--10°C, drying temperature of -50--10°C, vacuum degree of 1.3-13 Pa, and time of 48-72 hours.

[0048] In some embodiments of the present invention, the high temperature treatment is performed at a temperature of 40-90° C. and for a time of 10-60 min.

[0049] In the present invention, if the temperature or time of high temperature treatment exceeds the above parameter range, the lithium ion sieve nanofibers will be excessively cross-linked, resulting in stress concentration and affecting the mechanical properties and flexibility of the final aerogel.

[0050] The present invention also provides a gradient porous lithium ion sieve nanofiber aerogel prepared by the above preparation method.

[0051] The present invention also provides the use of the gradient porous lithium ion sieve nanofiber aerogel in the selective extraction of lithium from salt lakes and seawater with a high magnesium-to-lithium ratio.

[0052] The mechanism of the present invention is as follows:

[0053] The lithium ion sieve nanofiber aerogel prepared by the present invention must meet three requirements: first, uniform and stable preparation of pure lithium ion sieve nanofibers. By adding a certain amount of organic polymer, the lithium ion sieve is jet-drawn and crystallized under a high-voltage electric field to form fibers. The different content and type of organic polymer determine important parameters such as the fiberization difficulty, micromorphology, and polymer removal rate of the lithium ion sieve nanofibers. Second, uniform and stable lithium ion sieve nanofiber dispersion must be prepared. This requires nanofibers with a diameter of 200-950 nm and a length of 20-500 μm to ensure mild inter-fiber entanglement and avoid excessive aggregation, while also providing the necessary and sufficient fiber bonding points for subsequent chemical crosslinking. Third, crosslinking of the aerogel's three-dimensional network after freeze-drying is achieved. A certain amount of crosslinking agent is added to the dispersion to stabilize the structural stability of the lithium ion sieve nanofibers within the aerogel's three-dimensional network. Excessive amounts of crosslinking agent can easily block the active sites of the lithium ion sieve, resulting in a decrease in adsorption capacity. Excessive amounts of crosslinking agent can make it difficult to maintain structural stability in the aerogel and can easily lead to collapse of the three-dimensional network during application. Therefore, the amount of cross-linking agent selected determines the structure and application stability of lithium ion sieve nanofiber aerogel.

[0054] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0055] The preparation flow chart of the gradient porous lithium ion sieve nanofiber aerogel in the present invention is shown in Figure 1 .

[0056] The raw materials and reagents used in the examples can be obtained through commercial sources.

[0057] Example 1

[0058] This embodiment provides a gradient porous lithium ion sieve nanofiber aerogel, and the preparation steps are as follows:

[0059] S1: 0.4g H 1.6 Mn 1.6 O4 powder was mixed with 0.4 g of polyacrylonitrile in 10 mL of DMF and then ultrasonicated at 25 Hz for 10 min to obtain a spinning solution;

[0060] S2: The spinning solution obtained in S1 is electrospun to prepare H 1.6 Mn 1.6 The spinning parameters of the O4 precursor nanofiber membrane are as follows: voltage 22.5kV, liquid supply rate 1.0mL / min, receiving distance 15cm, drum speed 30r / min, the receiving fiber membrane material is oil-absorbing paper, spinning temperature 25℃, humidity 65%; the obtained H 1.6 Mn 1.6 The O4 precursor nanofiber membrane was vacuum dried at 80 °C for 12 h and then calcined in a muffle furnace at 400 °C for 5 h to obtain highly crystalline and flexible pure H 1.6 Mn 1.6 O4 nanofiber membrane;

[0061] S3: H obtained in S2 1.6 Mn 1.6 The O4 nanofiber membrane was cut into pieces and added into a mixed solution system containing trimethoxymethylsilane and oxalic acid (the solvent of the mixed solution system was deionized water and tert-butyl alcohol in a volume ratio of 4:1), and a homogenizer was used for high-speed shear dispersion to obtain H 1.6 Mn 1.6 O4 nanofiber dispersion; wherein the concentration of trimethoxymethylsilane in the mixed solution system is 0.4wt%, and the concentration of oxalic acid in the mixed solution system is 0.003wt%; the homogenization process conditions are: speed 8000rpm, time 2min; H 1.6 Mn 1.6 The concentration of nanofibers in the O4 nanofiber dispersion was 10 wt %, with an average diameter of 420 nm and an average length of 80 μm;

[0062] S4: H obtained in S3 1.6 Mn 1.6 The O4 nanofiber dispersion was transferred to a mold, frozen at -60°C, and then dried at -50°C and 2 Pa for 48 h to obtain uncrosslinked H 1.6 Mn 1.6O4 nanofiber aerogel; the aerogel was kept at 60℃ for 30min to obtain H 1.6 Mn 1.6 O4 nanofiber aerogel.

[0063] The obtained H 1.6 Mn 1.6 The lithium ion adsorption capacity of O4 nanofiber aerogel is 35.73 mg / g ( Figure 2 ). Figure 3 Demonstrated gradient porous H 1.6 Mn 1.6 Scanning electron microscopy (SEM) images and optical photographs (inset) of the pore structure at various levels in the O4 nanofiber aerogel show that it contains open cell micropores, macropores between nanofibers, and mesopores throughout the nanofibers. Figure 4 The cyclic compression curve shows that H 1.6 Mn 1.6 O4 nanofiber aerogel has structural stability and underwater flexibility.

[0064] Comparative Example 1

[0065] This comparative example provides a composite nanofiber aerogel, and the preparation steps are as follows:

[0066] S1: 0.4g H 1.6 Mn 1.6 O4 powder was mixed with 0.4 g of polyacrylonitrile (PAN) in 10 mL of DMF and then ultrasonicated at 25 Hz for 10 min to obtain a spinning solution;

[0067] S2: The spinning solution obtained in S1 is electrospun to prepare H 1.6 Mn 1.6 The spinning parameters of the O4 precursor nanofiber membrane are as follows: voltage 22.5kV, liquid supply rate 1.0mL / min, receiving distance 15cm, drum speed 30r / min, the receiving fiber membrane material is oil-absorbing paper, spinning temperature 25℃, humidity 65%; the obtained H 1.6 Mn 1.6 The O4 precursor nanofiber membrane was vacuum dried at 80 °C for 12 h to obtain a highly crystalline and flexible H 1.6 Mn 1.6 O4 / PAN composite nanofiber membrane;

[0068] S3: H obtained in S2 1.6 Mn 1.6 The O4 / PAN composite nanofiber membrane was cut into pieces and added into a mixed solution system containing trimethoxymethylsilane and oxalic acid (the solvent of the mixed solution system was deionized water and tert-butyl alcohol in a volume ratio of 4:1), and a homogenizer was used for high-speed shear dispersion to obtain H1.6 Mn 1.6 O4 / PAN composite nanofiber dispersion; wherein the concentration of trimethoxymethylsilane in the mixed solution system is 0.4wt%, and the concentration of oxalic acid in the mixed solution system is 0.003wt%; the homogenization process conditions are: speed 8000rpm, time 2min; H 1.6 Mn 1.6 The concentration of nanofibers in the O4 / PAN composite nanofiber dispersion was 10 wt %, with an average diameter of 465 nm and an average length of 76 μm;

[0069] S4: H obtained in S3 1.6 Mn 1.6 The O4 / PAN composite nanofiber dispersion was transferred to a mold, frozen at -60°C, and dried at -50°C and 2 Pa for 48 h to obtain uncrosslinked H 1.6 Mn 1.6 O4 / PAN composite nanofiber aerogel; the aerogel was kept at 60℃ for 30min to obtain H 1.6 Mn 1.6 O4 / PAN composite nanofiber aerogel.

[0070] The obtained H 1.6 Mn 1.6 The lithium ion adsorption capacity of O4 / PAN composite nanofiber aerogel was measured to be 5.77 mg / g.

[0071] Comparative Example 2

[0072] This comparative example provides a nanofiber aerogel, and the preparation steps are as follows:

[0073] S1: 0.4g H 1.6 Mn 1.6 O4 powder was mixed with 0.4 g of polyacrylonitrile in 10 mL of DMF and then ultrasonicated at 25 Hz for 10 min to obtain a spinning solution;

[0074] S2: The spinning solution obtained in S1 is electrospun to prepare H 1.6 Mn 1.6 The spinning parameters of the O4 precursor nanofiber membrane are as follows: voltage 22.5kV, liquid supply rate 1.0mL / min, receiving distance 15cm, drum speed 30r / min, the receiving fiber membrane material is oil-absorbing paper, spinning temperature 25℃, humidity 65%; the obtained H 1.6 Mn 1.6 The O4 precursor nanofiber membrane was vacuum dried at 80 °C for 12 h and then calcined in a muffle furnace at 400 °C for 5 h to obtain highly crystalline and flexible pure H 1.6 Mn 1.6O4 nanofiber membrane;

[0075] S3: H obtained in S2 1.6 Mn 1.6 The O4 nanofiber membrane was cut into pieces and added into a mixed solution system containing trimethoxymethylsilane and oxalic acid (the solvent of the mixed solution system was deionized water and tert-butyl alcohol in a volume ratio of 4:1), and a homogenizer was used for high-speed shear dispersion to obtain H 1.6 Mn 1.6 O4 nanofiber dispersion; wherein the concentration of trimethoxymethylsilane in the mixed solution system is 0.4wt%, and the concentration of oxalic acid in the mixed solution system is 0.003wt%; the homogenization process conditions are: speed 8000rpm, time 2min; H 1.6 Mn 1.6 The concentration of nanofibers in the O4 nanofiber dispersion was 10 wt %, with an average diameter of 405 nm and an average length of 85 μm;

[0076] S4: H obtained in S3 1.6 Mn 1.6 The O4 nanofiber dispersion was transferred to a mold, frozen at -60°C, and then dried at -50°C and 2 Pa for 48 h to obtain uncrosslinked H 1.6 Mn 1.6 O4 nanofiber aerogel.

[0077] The obtained uncrosslinked H 1.6 Mn 1.6 The lithium ion adsorption capacity of O4 nanofiber aerogel is 30.89 mg / g; the uncrosslinked H 1.6 Mn 1.6 O4 nanofiber aerogel is not flexible and elastic, and the three-dimensional network structure of the aerogel has collapsed during immersion or adsorption in water.

[0078] Example 2

[0079] This embodiment provides a gradient porous lithium ion sieve nanofiber aerogel, and the preparation steps are as follows:

[0080] S1: 0.4 g HMn2O4 powder and 0.8 g polyvinyl alcohol were mixed in 10 mL ethanol and then ultrasonicated at 40 Hz for 10 min to obtain a spinning solution;

[0081] S2: The spinning solution obtained in S1 was subjected to electrospinning to prepare an HMn2O4 precursor nanofiber membrane. The spinning parameters were: voltage 30 kV, liquid supply rate 1.5 mL / min, receiving distance 15 cm, drum speed 30 r / min, the receiving fiber membrane material was oil-absorbing paper, spinning temperature was 25°C, and humidity was 70%; the obtained HMn2O4 precursor nanofiber membrane was vacuum dried at 80°C for 12 h, and then calcined in a muffle furnace at 800°C for 4 h to obtain a highly crystalline and flexible pure HMn2O4 nanofiber membrane;

[0082] S3: The HMn2O4 nanofiber membrane obtained in S2 was cut into pieces and added to a mixed solution system containing (3-methoxypropyl)trimethoxysilane and oxalic acid (the solvent of the mixed solution system is deionized water and tert-butanol in a volume ratio of 4:1), and a homogenizer was used for high-speed shear dispersion to obtain an HMn2O4 nanofiber dispersion; wherein the concentration of (3-methoxypropyl)trimethoxysilane in the mixed solution system is 0.2wt%, and the concentration of oxalic acid in the solution system is 0.003wt%; the homogenization process conditions are: rotation speed 5000rpm, time 5min; the concentration of nanofibers in the HMn2O4 nanofiber dispersion is 8wt%, the average diameter is 850nm, and the average length is 65μm;

[0083] S4: The HMn2O4 nanofiber dispersion obtained in S3 was transferred to a mold, frozen at -60°C, and dried at -50°C and 10Pa for 70 hours to obtain an uncrosslinked HMn2O4 nanofiber aerogel; the aerogel was kept at 90°C for 50 minutes to obtain an HMn2O4 nanofiber aerogel.

[0084] The lithium ion adsorption capacity of the obtained HMn2O4 nanofiber aerogel is 32.60 mg / g.

[0085] Example 3

[0086] This embodiment provides a gradient porous lithium ion sieve nanofiber aerogel, and the preparation steps are as follows:

[0087] S1: 0.4 g H2MnO3 powder and 0.6 g polyvinyl pyrrolidone were mixed in 10 mL ethanol and then ultrasonicated at 40 Hz for 10 min to obtain a spinning solution;

[0088] S2: The spinning solution obtained in S1 was subjected to electrospinning to prepare a H2MnO3 precursor nanofiber membrane. The spinning parameters were: voltage 30 kV, liquid supply rate 1.5 mL / min, receiving distance 15 cm, drum speed 30 r / min, the receiving fiber membrane material was oil-absorbing paper, spinning temperature was 25°C, and humidity was 70%; the obtained HMn2O4 precursor nanofiber membrane was vacuum dried at 80°C for 12 h, and then calcined in a muffle furnace at 600°C for 5 h to obtain a highly crystalline and flexible pure H2MnO3 nanofiber membrane;

[0089] S3: The H2MnO3 nanofiber membrane obtained in S2 was cut into pieces and added to a mixed solution system containing 3-aminopropyltriethoxysilane and oxalic acid (the solvent of the mixed solution system is deionized water and tert-butanol in a volume ratio of 4:1), and a homogenizer was used for high-speed shear dispersion to obtain an H2MnO3 nanofiber dispersion; wherein the concentration of 3-aminopropyltriethoxysilane in the mixed solution system is 0.2wt%, and the concentration of oxalic acid in the mixed solution system is 0.003wt%; the homogenization process conditions are: rotation speed 10000rpm, time 5min; the concentration of nanofibers in the H2MnO3 nanofiber dispersion is 10wt%, the average diameter is 350nm, and the average length is 98μm;

[0090] S4: The H2MnO3 nanofiber dispersion obtained in S3 was transferred to a mold, frozen at -60°C, and dried at -30°C and 10Pa for 60 hours to obtain an uncrosslinked H2MnO3 nanofiber aerogel; the aerogel was kept warm at 50°C for 40 minutes to obtain an H2MnO3 nanofiber aerogel.

[0091] The lithium ion adsorption capacity of the obtained H2MnO3 nanofiber aerogel is 42.50 mg / g.

[0092] Example 4

[0093] This embodiment provides a gradient porous lithium ion sieve nanofiber aerogel, and the preparation steps are as follows:

[0094] S1: 0.4 g H2TiO3 powder and 0.4 g polyacrylamide were mixed in 10 mL DMF and then ultrasonicated at 40 Hz for 10 min to obtain a spinning solution;

[0095] S2: The spinning solution obtained in S1 was subjected to electrospinning to prepare a H2TiO3 precursor nanofiber membrane. The spinning parameters were: voltage 30 kV, liquid supply rate 1.5 mL / min, receiving distance 15 cm, drum speed 30 r / min, the receiving fiber membrane material was oil-absorbing paper, spinning temperature was 25°C, and humidity was 70%; the obtained H2TiO3 precursor nanofiber membrane was vacuum dried at 80°C for 12 h, and then calcined in a muffle furnace at 500°C for 5 h to obtain a highly crystalline and flexible pure H2TiO3 nanofiber membrane;

[0096] S3: The H2TiO3 nanofiber membrane obtained in S2 was cut into pieces and added to a mixed solution system containing trimethoxymethylsilane and oxalic acid (the solvent of the mixed solution system was deionized water and tert-butanol in a volume ratio of 4:1), and a homogenizer was used for high-speed shear dispersion to obtain a H2TiO3 nanofiber dispersion; wherein the concentration of trimethoxymethylsilane in the mixed solution system was 0.2wt%, and the concentration of oxalic acid in the mixed solution system was 0.003wt%; the homogenization process conditions were: a rotation speed of 10000rpm, a time of 5min; the concentration of nanofibers in the H2TiO3 nanofiber dispersion was 10wt%, the average diameter was 520nm, and the average length was 83μm;

[0097] S4: The H2TiO3 nanofiber dispersion obtained in S3 was transferred to a mold, frozen at -60°C, and dried at -30°C and 10Pa for 60 hours to obtain an uncrosslinked H2TiO3 nanofiber aerogel; the aerogel was kept at 50°C for 40 minutes to obtain an H2TiO3 nanofiber aerogel.

[0098] The lithium ion adsorption capacity of the obtained H2TiO3 nanofiber aerogel is 46.85 mg / g.

[0099] Example 5

[0100] This embodiment provides a gradient porous lithium ion sieve nanofiber aerogel, and the preparation steps are as follows:

[0101] S1: 0.4g H4Ti5O 12 The powder was mixed with 0.4 g of polyvinyl alcohol in 10 mL of ethanol and then ultrasonicated at 40 Hz for 10 min to obtain a spinning solution;

[0102] S2: The spinning solution obtained in S1 is electrospun to prepare H4Ti5O 12The spinning parameters of the precursor nanofiber membrane are as follows: voltage 30 kV, liquid supply rate 1.5 mL / min, receiving distance 15 cm, drum speed 30 r / min, the receiving fiber membrane material is oil-absorbing paper, spinning temperature 25 ° C, humidity 70%; the obtained H2TiO3 precursor nanofiber membrane is vacuum dried at 80 ° C for 12 h, and then calcined in a muffle furnace at 600 ° C for 3 h to obtain highly crystalline and flexible pure H4Ti5O 12 nanofiber membranes;

[0103] S3: H4Ti5O obtained in S2 12 The nanofiber membrane was cut into pieces and added into a mixed solution system containing trimethoxymethylsilane and oxalic acid (the solvent of the mixed solution system was deionized water and tert-butyl alcohol in a volume ratio of 4:1). The nanofiber membrane was dispersed by high-speed shearing using a homogenizer to obtain H4Ti5O 12 Nanofiber dispersion; wherein the concentration of trimethoxymethylsilane in the mixed solution system is 0.2wt%, and the concentration of oxalic acid in the mixed solution system is 0.003wt%; the homogenization process conditions are: speed 5000rpm, time 10min; H4Ti5O 12 The nanofiber concentration in the nanofiber dispersion was 12 wt %, the average diameter was 880 nm, and the average length was 65 μm;

[0104] S4: H4Ti5O obtained in S3 12 The nanofiber dispersion was transferred to a mold, frozen at -80 °C, and then dried at -50 °C and 5 Pa for 48 h to obtain uncrosslinked H4Ti5O 12 Nanofiber aerogel; the aerogel was kept at 90℃ for 20min to obtain H4Ti5O 12 Nanofiber aerogel.

[0105] The obtained H4Ti5O 12 The lithium ion adsorption capacity of the nanofiber aerogel is 65.20 mg / g.

[0106] Example 6

[0107] This embodiment provides a gradient porous lithium ion sieve nanofiber aerogel, and the preparation steps are as follows:

[0108] S1: 0.4 g of HCl·2Al(OH)3 powder and 0.4 g of polyvinylidene fluoride were mixed in 10 mL of DMF and then ultrasonicated at 50 Hz for 15 min to obtain a spinning solution;

[0109] S2: The spinning solution obtained in S1 was subjected to electrospinning to prepare an HCl·2Al(OH)3 precursor nanofiber membrane. The spinning parameters were: voltage 30 kV, liquid supply rate 1.5 mL / min, receiving distance 15 cm, drum speed 30 r / min, the receiving fiber membrane material was oil-absorbing paper, the spinning temperature was 25°C, and the humidity was 70%; the obtained HCl·2Al(OH)3 precursor nanofiber membrane was vacuum dried at 80°C for 12 h, and then calcined in a muffle furnace at 800°C for 3 h to obtain a highly crystalline and flexible pure HCl·2Al(OH)3 nanofiber membrane;

[0110] S3: The HCl·2Al(OH)3 nanofiber membrane obtained in S2 was cut into pieces and added into a mixed solvent system containing 3-aminopropyltriethoxysilane and oxalic acid (the solvent of the mixed solution system is deionized water and tert-butanol in a volume ratio of 4:1) and dispersed by high-speed shearing using a homogenizer to obtain an HCl·2Al(OH)3 nanofiber dispersion; wherein the concentration of 3-aminopropyltriethoxysilane in the mixed solution system is 0.2wt%, and the concentration of oxalic acid in the mixed solution system is 0.003wt%; the homogenization process conditions are: rotation speed 6000rpm, time 7min; the concentration of nanofibers in the HCl·2Al(OH)3 nanofiber dispersion is 12wt%, the average diameter is 950nm, and the average length is 60μm;

[0111] S4: The HCl·2Al(OH)3 nanofiber dispersion obtained in S3 was transferred to a mold, frozen at -30°C, and dried at -30°C and 5Pa for 65 hours to obtain uncross-linked HCl·2Al(OH)3 nanofiber aerogel; the aerogel was kept warm at 60°C for 30 minutes to obtain HCl·2Al(OH)3 nanofiber aerogel.

[0112] The lithium ion adsorption capacity of the obtained HCl·2Al(OH)3 nanofiber aerogel is 12.30 mg / g.

[0113] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing gradient porous lithium ion sieve nanofiber aerogel, characterized in that: The following steps are involved: The lithium ion sieve and the organic polymer are dissolved in a solvent to obtain a spinning solution, and then the spinning solution is electrospinned to obtain a lithium ion sieve precursor nanofiber membrane; calcining the lithium ion sieve precursor nanofiber membrane at high temperature to obtain a pure lithium ion sieve nanofiber membrane; The pure lithium ion sieve nanofiber membrane is dispersed in a solution system containing a crosslinking agent and a catalyst, and then the obtained lithium ion sieve nanofiber dispersion is freeze-dried and high-temperature treated in sequence to obtain the gradient porous lithium ion sieve nanofiber aerogel; The crosslinking agent is at least one of trimethoxymethylsilane, (3-methoxypropyl)trimethoxysilane and 3-aminopropyltriethoxysilane; the concentration of the crosslinking agent in the lithium ion sieve nanofiber dispersion is 0.1-0.5wt%; The catalyst is oxalic acid; the concentration of the catalyst in the lithium ion sieve nanofiber dispersion is 0-0.005wt%.

2. The method for preparing the gradient porous lithium ion sieve nanofiber aerogel according to claim 1, characterized in that: The lithium ion sieve is H 1.6 Mn 1.6 O4, HMn2O4, H2MnO3, H2TiO3, H4Ti5O 12 and at least one of HCl·2Al(OH)3; the mass ratio of the lithium ion sieve to the organic polymer is 1:(0.5-2).

3. The method for preparing the gradient porous lithium ion sieve nanofiber aerogel according to claim 1, characterized in that: The organic polymer is at least one of polyacrylonitrile, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, nylon 6 and polyvinylidene fluoride; and the concentration of the organic polymer in the spinning solution is 4-15 wt%.

4. The method for preparing the gradient porous lithium ion sieve nanofiber aerogel according to claim 1, characterized in that: The high-temperature calcination temperature is 400-800° C. and the time is 2-10 hours.

5. The method for preparing the gradient porous lithium ion sieve nanofiber aerogel according to claim 1, characterized in that: The concentration of the lithium ion sieve nanofibers in the lithium ion sieve nanofiber dispersion is 5-15 wt %; the diameter of the lithium ion sieve nanofibers is 200-950 nm, and the length is 20-500 μm.

6. The method for preparing the gradient porous lithium ion sieve nanofiber aerogel according to claim 1, characterized in that: The freeze-drying parameters are: freezing temperature of -197--10°C, drying temperature of -50--10°C, vacuum degree of 1.3-13 Pa, and time of 48-72 hours.

7. The method for preparing the gradient porous lithium ion sieve nanofiber aerogel according to claim 1, characterized in that: The temperature of the high temperature treatment is 40-90° C. and the time is 10-60 minutes.

8. A gradient porous lithium ion sieve nanofiber aerogel prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the gradient porous lithium ion sieve nanofiber aerogel according to claim 8 in the selective extraction of lithium from salt lakes and seawater with a high magnesium-to-lithium ratio.

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