Multilayer pre-alkalization nanofiber-based photo-thermal lithium ion sieve as well as preparation method and application thereof

Abstract

The invention discloses a multi-layer pre-alkalization nanofiber-based photo-thermal lithium ion sieve and a preparation method and application thereof, the pre-alkalization nanofiber-based photo-thermal lithium ion sieve with a multi-layer structure is prepared by adopting an extensible textile technology, and the structure of the multi-layer pre-alkalization nanofiber-based photo-thermal lithium ion sieve is composed of a hydrophilic fabric at the bottom, a pre-alkalization layer in the middle and a photo-thermal lithium extraction layer at the top. Through integration of multiple layers of functions, the problems that H1. 6Mn1. 6O4 is low in reuse performance, poor in adsorption performance in a normal state, lack of adsorption kinetics and the like are successfully solved, and synergistic alkalization and photo-thermal activation of the multi-layer pre-alkalization nanofiber-based photo-thermal lithium ion sieve are achieved; an effective scheme is provided for sustainable extraction of lithium resources from salt lake water and water circulation, and many obstacles of a traditional lithium extraction technology are overcome.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion sieve technology, specifically to a multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve, its preparation method, and its application. Background Technology

[0002] Lithium resources, hailed as the "white oil" of the 21st century, are a key strategic resource for electrification and decarbonization, widely used in new energy vehicles and energy storage systems for electronic devices. Demand is growing exponentially, leading to resource shortages. my country primarily obtains lithium resources through mining terrestrial lithium ores and extraction from water resources. Seawater and salt lakes have richer lithium reserves, but lithium extraction from salt lakes faces significant challenges due to the complex aquatic environment. Among numerous lithium extraction technologies from salt lakes and seawater, direct adsorption using lithium-ion sieves is considered the most promising due to its low energy consumption and environmental friendliness. Among these technologies, manganese oxide H... 1.6 Mn 1.6 O4 (HMO) is widely used due to its high adsorption capacity and excellent ion selectivity. However, low lithium ion concentration and complex multi-ion environment make its extraction difficult and energy consumption relatively high. The main problems include: the alkaline activity of HMO affects the adsorption electrostatic potential energy and ion exchange capacity; and insufficient alkaline activity in the natural environment easily leads to the accumulation of H+. + Inhibit Li + Adsorption is difficult, but precise control of the overall alkalinity of salt lakes is challenging, and over-alkaliization can cause ion precipitation and HMO damage. HMO lithium adsorption is an endothermic ion exchange reaction, and insufficient heat under natural conditions limits adsorption activity and kinetics, thus restricting efficiency improvement. Particulate HMO has poor fluidity and permeability, and the loss during acid washing for lithium extraction limits recycling. Therefore, it is necessary to develop HMO carriers and expand adsorption active sites to balance efficiency and stability.

[0003] To alleviate the contradiction between lithium resource shortages and increasing supply and demand, researchers have developed various materials and technologies for extracting lithium from aquatic environments. However, existing technologies have fundamental flaws: nanofiltration separation technology is not suitable for monovalent Li. + and Na + Low selectivity; precipitation methods are prone to co-precipitation with other metals, resulting in low product concentrations and slow kinetics; electrochemical lithium extraction requires additional electrical energy and electrolytes, and also produces gaseous byproducts. With the deepening research on adsorption materials, the feasibility of lithium extraction by adsorption methods has become apparent. HMO has become a research hotspot due to its high capacity, excellent selectivity, and good cycling stability, but it still faces the above challenges. It is necessary to develop alkali-activated support ion sieves with precise interfacial alkalinity control and the required active adsorption sites.

[0004] Existing related technical solutions also have obvious shortcomings: the photothermal assisted lithium extraction nonwoven material of invention patent CN116966866A requires the addition of a large amount of alkaline substance in advance to adsorb Li. +This can easily cause environmental pollution; the porous manganese-based ion sieve precursor in invention patent CN118978182A has poor circulation performance and suffers severe dissolution after repeated use; the solar lithium extraction equipment in invention patent CN115198113A does not consider Li + The overall recovery efficiency is low, and the process is lengthy. The core-shell structured photothermal driven ion sieve developed by Professor Xu Zhikang and Researcher Zhang Chao's team at Zhejiang University struggles to achieve efficient lithium ion extraction under normal conditions, sometimes even failing to meet the extraction target. This process requires pre-alkalization of the lithium-containing solution; however, excessive alkalinity leads to an increase in Mg content in the solution. 2+ Ca 2+ When competing ions precipitate, they significantly affect the lithium extraction efficiency of lithium-ion sieves and cause irreversible damage to their microstructure. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of low reusability, poor normal adsorption performance and lack of adsorption kinetics of HMO in the prior art, and to provide a multilayer pre-alkalized nanofiber-based photothermal lithium ion sieve, its preparation method and application.

[0006] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0007] The first aspect of this invention provides a method for preparing a multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve (APLS), comprising the following steps:

[0008] (1) Dissolve an alkaline salt in a cellulose acetate (CA) solution to obtain a spinning solution, and perform electrospinning on a hydrophilic fabric substrate using the spinning solution to form a pre-alkalized layer.

[0009] (2) H 1.6 Mn 1.6 O4(HMO) particles are dispersed in polymer solution A to obtain spinning solution A, and photothermal nanoparticles are dispersed in polymer solution B to obtain spinning solution B. Coaxial electrospinning is performed using spinning solution A as the sheath spinning solution and spinning solution B as the core spinning solution to form a photothermal lithium extraction layer with a core-sheath structure.

[0010] (3) The photothermal lithium extraction layer is covered on the pre-alkalization layer on the hydrophilic fabric substrate to obtain the multilayer pre-alkalized nanofiber-based photothermal lithium ion sieve.

[0011] This invention employs scalable textile technology to prepare a pre-alkalized nanofiber-based photothermal lithium-ion sieve with a multi-layer structure, which consists of a bottom hydrophilic nonwoven fabric (hydrophilic fabric), a middle alkali-activated membrane (pre-alkalized layer), and a top photothermal ion sieve (photothermal lithium extraction layer).

[0012] Hydrophilic fabric, serving as both the base material and supporting framework, ensures efficient transport of water and ions while maintaining the overall structural stability. A nanofiber-based lithium-ion sieve, prepared by electrospinning HMO particles dispersed in a PAN solution, effectively addresses the severe loss and manganese dissolution issues associated with HMO particle recycling and reuse. Furthermore, leveraging the high specific surface area, high porosity, and strong reusability of nanofibers, along with the hydrophilicity of PAN, this nanofiber-based lithium-ion sieve can easily adsorb Li from the aquatic environment. + .

[0013] When the neutral brine flows through the middle alkali-activated layer, the alkaline salt (such as Na2CO3 particles) has been successfully loaded into the layer by electrospinning technology. After the alkaline salt comes into contact with water, it undergoes a hydrolysis reaction, which can generate a large amount of alkaline active substances (OH-). These substances reach the top interface layer through capillary forces and ion transport, thus ensuring the normal adsorption of HMO without the addition of additional alkaline substances.

[0014] The photothermal lithium extraction layer is prepared using coaxial electrospinning technology, with PAN / HMO nanofibers as the sheath layer and PAN / CB nanofibers as the core layer. This core-sheath structure of the photothermal lithium-ion sieve membrane can alleviate the performance limitations caused by nanofiber aggregation. Simultaneously, the heat generated by photothermal conversion can activate adsorption kinetics, promoting water evaporation to produce fresh water while enriching ions in the water at the evaporation interface layer, further promoting Li-ion extraction. + Adsorption.

[0015] In summary, through the integration of multiple functions, this invention successfully solves the problems of low reusability, poor adsorption performance under normal conditions, and lack of adsorption kinetics inherent in HMOs. It achieves synergistic alkalization and photothermal activation of APLS, providing an effective solution for the sustainable extraction of lithium resources and water recycling from saline lake water, overcoming many obstacles of traditional lithium extraction technologies. Compared to traditional ion sieves that require complex pre-control of saline lake alkalinity and temperature to achieve lithium extraction, the APLS of this invention can directly achieve adaptive photothermal drive and online fine-tuning of alkali activity in the natural environment, effectively solving the problem of ion precipitation caused by over-alkalization affecting lithium extraction efficiency.

[0016] Further, in step (1), the alkaline salt is a strong base weak acid salt, such as K2CO3, NaHCO3, Na2CO3, etc., preferably Na2CO3.

[0017] Further, in step (1), the concentration of cellulose acetate in the cellulose acetate solution is 13-15 wt%.

[0018] Further, in step (1), the solvent of the cellulose acetate solution is a mixed solvent of acetone and N,N-dimethylacetamide, wherein the mass ratio of acetone to N,N-dimethylacetamide is (1.5-2.5):1, preferably 2:1.

[0019] Further, in step (1), the concentration of the alkaline salt in the spinning solution is 3-18 wt%.

[0020] Furthermore, in step (1), the electrospinning process parameters include: a spinning needle flow rate of 1.0-1.4 mL·h. -1 The distance between the needle and the collector is 14-16cm, and the operating voltage is 13-15kV.

[0021] Further, in step (1), the hydrophilic fabric substrate is a hydrophilic nonwoven fabric substrate, cotton fabric, or hydrophilic polypropylene (PP) fabric.

[0022] Further, in step (1), the hydrophilic fabric substrate is pretreated, specifically by placing the hydrophilic fabric in an ethanol solution for cleaning to remove impurities and contaminants from the surface and interior of the hydrophilic fabric.

[0023] Further, in step (2), the H 1.6 Mn 1.6 The particle size of O4 particles is 50-150 nm.

[0024] Further, in step (2), the H 1.6 Mn 1.6 The preparation method of O4 particles includes the following steps: mixing lithium source and manganese source, followed by hydrothermal reaction and calcination to obtain a precursor, and then acid washing the precursor to obtain the H. 1.6 Mn 1.6 O4 particles.

[0025] Furthermore, the lithium source is lithium hydroxide monohydrate, and the manganese source includes potassium permanganate and manganese nitrate tetrahydrate.

[0026] Furthermore, the hydrothermal reaction is carried out at a temperature of 150-170°C for a duration of 20-28 hours.

[0027] Furthermore, the calcination temperature is 380-420℃, and the holding time is 5-7h.

[0028] Furthermore, the precursor is Li 1.6 Mn 1.6 O4(LMO).

[0029] Furthermore, the pickling treatment uses hydrochloric acid and the treatment time is 20-28 hours.

[0030] Further, in step (2), the polymer in the polymer solution A is selected from one or more of polyacrylonitrile (PAN), polyvinyl chloride (PVC) and ethylene-vinyl alcohol copolymer (EVOH).

[0031] Further, in step (2), the solvent of the polymer solution A is selected from one or more of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and N,N-dimethylacetamide (DMAc).

[0032] Furthermore, in step (2), the polymer content in the spinning solution A is 6-11 wt%. The viscosity of the spinning solution is a key factor determining the morphology of electrospun fibers, and the viscosity of the polymer mainly depends on its content in the spinning solution.

[0033] Further, in step (2), H in the spinning solution A 1.6 Mn 1.6 The content of O4 particles is 6-14 wt%.

[0034] Further, in step (2), the polymer in the polymer solution B is selected from one or more of polyacrylonitrile (PAN), polyvinyl chloride (PVC) and ethylene-vinyl alcohol copolymer (EVOH).

[0035] Further, in step (2), the solvent of the polymer solution B is selected from one or more of dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and N,N-dimethylacetamide (DMAc).

[0036] Furthermore, in step (2), the polymer content in the spinning solution B is 6-11 wt%.

[0037] Furthermore, in step (2), the content of photothermal nanoparticles in the spinning solution B is 1-5 wt%.

[0038] Further, in step (2), the photothermal nanoparticles are selected from one or more of carbon black (CB), polypyrrole (PPy), gold nanoparticles, silver nanoparticles and MXene nanoparticles, preferably CB.

[0039] Furthermore, in step (2), the process parameters for coaxial electrospinning include: the propulsion rate of the sheath spinning solution is 0.7-0.9 mL·h. -1 The propulsion rate of the core spinning solution is 0.7-0.8 mL·h. -1 The distance between the coaxial needle and the collector is 14-16cm, and the operating voltage is 15-17kV.

[0040] Furthermore, in step (2), the diameter of the core layer of the fiber obtained by coaxial electrospinning is 120-140 nm, and the thickness of the sheath layer is 60-80 nm.

[0041] In step (3), the photothermal lithium extraction layer is covered on the pre-alkalized layer on the hydrophilic fabric substrate. Thanks to the excellent hydrophilic properties of each layer, the multilayer pre-alkalized nanofiber-based photothermal lithium ion screen can form a tight adhesion between each layer after contacting the water body. Even if subjected to conventional mechanical forces, it will not detach, and the structural stability is significant.

[0042] The second aspect of the present invention provides a multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve prepared by the preparation method described in the first aspect.

[0043] The multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve of this invention can effectively accelerate the lithium extraction process by activating molecular motion and reducing the chemical barrier. The synergistic activation of alkalinity and photothermal properties plays a crucial role: alkaline activation reduces electrostatic potential energy, increases adsorption chemical energy, expands adsorption active sites, and accelerates adsorption kinetics; photothermal activation, through interfacial evaporation induced by solar radiation, further promotes capillary wicking and surface Li-ion adsorption. + Enrichment occurs, and the heat generated by photothermal conversion significantly activates adsorption kinetics. Under the combined effect of these two factors, the adsorption kinetics of the lithium-ion sieve are accelerated, and its adsorption capacity is significantly enhanced.

[0044] This invention, through nanofiber engineering design, not only ensures the cycling stability of HMO, but also precisely controls the electrostatic potential, chemical potential, adsorption active sites, and nano-ion distribution, thereby comprehensively promoting the efficient extraction of lithium.

[0045] The third aspect of this invention provides an application of the multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve described in the second aspect in lithium extraction from salt lakes.

[0046] Inspired by the growth of halophytes in salt lakes, this invention prepares a multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve by regulating the fiber composition and structure, which has the following beneficial effects:

[0047] 1. Highly efficient online control of confined alkali activity was achieved. Alkaline salts were electrospun into nanofiber membranes as a pre-alkalization layer. When salt lake water was transported to the surface of the ion sieve under capillary force, the alkali activity of the ion sieve could be precisely controlled through the hydrolysis reaction of the alkaline salts. This eliminated the need for complex pre-control of the overall alkalinity of the salt lake, effectively avoiding ion precipitation and damage to the ion sieve structure caused by over-alkalization. Simultaneously, it reduced the electrostatic potential energy, providing a more suitable environment for Li... + Adsorption creates a suitable chemical environment.

[0048] 2. Significantly improved lithium adsorption performance and kinetics. The photothermal lithium-ion sieve is formed by coaxial electrospinning into composite nanofibers consisting of a sheath layer of HMO and a core layer of photothermal nanoparticles. The outer HMO provides abundant active sites for lithium adsorption, while the inner CB provides localized heat through photothermal conversion. Under solar radiation, interfacial photothermal evaporation drives ion enrichment, increases adsorption concentration, and activates adsorption kinetics; alkaline activation promotes the HMO at its 8a and 16d sites. + A neutralization reaction occurs, creating crystal vacancies that allow Li to... + The exposed active sites were completely adsorbed, and the synergistic effect of the two significantly accelerated the lithium extraction process, achieving a lithium extraction performance of 24.92 mg·g under 1 sun light intensity. -1 .

[0049] 3. Optimized lithium-magnesium separation effect and cycle stability. With the help of nanofiber engineering design, APLS can precisely adjust the chemical potential energy, adsorption active sites and nano-ion distribution, achieving a lithium-magnesium separation coefficient of up to 6248 in real Qinghai Emerald Lake water; at the same time, the fiber structure effectively solves the problem of HMO particle loss and dissolution, ensuring the cycle stability of the lithium ion screen and extending its service life.

[0050] 4. Excellent environmental adaptability and practicality. Compared with traditional ion sieves that require complex pre-control of alkalinity and temperature in salt lakes to achieve lithium extraction, the APLS of this invention can directly achieve adaptive confined photothermal and alkaline activity micro-control in natural environments (pH can be adjusted to 11.5). It does not require complicated pretreatment equipment and steps, has low energy consumption, is easy to operate, and can directly and efficiently extract lithium resources from salt lakes. It has broad application prospects and extremely strong practical value. Attached Figure Description

[0051] Figure 1 This is a schematic diagram illustrating the preparation of the multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve of the present invention.

[0052] Figure 2 The graph shows the lithium extraction performance test results of LS with different PAN contents in Comparative Examples 1-6.

[0053] Figure 3 The graph shows the lithium extraction performance test results of PAN / HMO nanofiber-based lithium-ion sieves with different HMO particle contents in Comparative Examples 3 and 7-12.

[0054] Figure 4 The figures show the pH adjustment performance and lithium adsorption performance of Na2CO3 / cellulose acetate composite nanofiber-based alkali-activated lithium ion sieves with different Na2CO3 contents in Comparative Example 3 (LS) and Comparative Examples 13-18 (LS). In the figure, a is the pH adjustment performance figure and b is the lithium adsorption performance figure.

[0055] Figure 5Solar absorbance data for PAN, ALS4 (Comparative Example 16), and APLS (Examples 1-5) in the 250-2500 nm range.

[0056] Figure 6 The graph shows the lithium adsorption performance of the LS of Comparative Example 3 and the multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieves with different CB contents in Examples 1-5 under dark and light conditions.

[0057] Figure 7 The graph shows the lithium adsorption performance of the nanofiber-based photothermal lithium-ion sieves APLS3 (Example 3), Comparative Example 19, and Comparative Example 20 under illumination conditions.

[0058] Figure 8 Figure 1 shows the results of the indoor photothermal lithium extraction experiment of APLS3 in Example 3; where a is the lithium adsorption performance under different solar radiation, b is the comparison of lithium adsorption performance under different temperatures with and without light, and c is the cycle performance of APLS3.

[0059] Figure 9 The graph shows the ion sieving performance of APLS3 in the water of Qinghai Emerald Salt Lake in Example 3. Detailed Implementation

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0061] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0062] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0063] The preparation method of HMO particles in the following examples and comparative examples includes the following steps: 3 mol of lithium hydroxide monohydrate, 0.015 mol of potassium permanganate, and 0.06 mol of manganese nitrate tetrahydrate were added to 85 mL of deionized water, and then transferred to a reaction vessel for hydrothermal treatment at 160 °C for 24 h. The obtained intermediate product was placed in a muffle furnace and held at 400 °C for 6 h to obtain the lithium-ion sieve precursor Li. 1.6 Mn 1.6O4 (LMO). Finally, LMO was poured into 0.3 mol / L hydrochloric acid and dispersed for 24 h to obtain lithium-ion sieve HMO particles with a particle size of about 100 nm.

[0064] Example 1

[0065] A method for preparing a multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve (APLS1), the preparation schematic diagram is shown below. Figure 1 As shown, it includes the following steps:

[0066] (1) Na₂CO₃ was dissolved in a CA solution (solvents were acetone and N,N-dimethylacetamide, mass ratio 2:1, CA concentration 14 wt%) to obtain a spinning solution, wherein the concentration of Na₂CO₃ in the spinning solution was 12 wt%. Commercial hydrophilic nonwoven fabric was washed in an ethanol solution to remove impurities and contaminants from the fabric surface and interior. The washed hydrophilic nonwoven fabric was fixed on a roller collector as a substrate, and electrospinning was performed on the hydrophilic nonwoven fabric substrate using the spinning solution at a spinning needle flow rate of 1.2 mL·h. -1 The distance between the needle and the collector is 15cm, the working voltage is 14kV, and a pre-alkalization layer is formed.

[0067] (2) HMO particles were dispersed in PAN solution A (solvent: DMF) to obtain spinning solution A, in which the content of PAN in spinning solution A was 8 wt% and the content of HMO particles in spinning solution A was 11 wt%; CB was dispersed in PAN solution B (solvent: DMF) to obtain spinning solution B, in which the content of CB in spinning solution B was 1 wt%; 3 mL of each of spinning solution A and spinning solution B were placed in a coaxially connected syringe, and coaxial electrospinning was performed with spinning solution A as the sheath spinning solution and spinning solution B as the core spinning solution. The propulsion rate of the sheath spinning solution was 0.8 mL·h. -1 The propulsion rate of the core spinning solution is 0.75 mL·h. -1 The distance between the coaxial needle and the collector is 15cm, and the working voltage is 16kV, forming a photothermal lithium extraction layer with a core-sheath structure.

[0068] (3) The photothermal lithium extraction layer is covered on the pre-alkalization layer on the hydrophilic nonwoven fabric substrate to obtain the multi-layer pre-alkalized nanofiber-based photothermal lithium ion sieve, named APLS1.

[0069] Example 2

[0070] A method for preparing a multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve (APLS2) is basically the same as that in Example 1, except that in step (2), the content of CB in spinning solution B is 2wt%.

[0071] Example 3

[0072] A method for preparing a multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve (APLS3) is basically the same as that in Example 1, except that in step (2), the content of CB in spinning solution B is 3wt%.

[0073] Example 4

[0074] A method for preparing a multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve (APLS4) is basically the same as that in Example 1, except that in step (2), the content of CB in spinning solution B is 4 wt%.

[0075] Example 5

[0076] A method for preparing a multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve (APLS5) is basically the same as that in Example 1, except that in step (2), the content of CB in spinning solution B is 5 wt%.

[0077] Comparative Example 1

[0078] A method for preparing a PAN / HMO nanofiber-based lithium-ion sieve (LS) includes the following steps:

[0079] HMO particles were dispersed in a PAN solution (solvent: DMF) to obtain a spinning solution containing 6 wt% PAN and 11 wt% HMO particles. Commercial hydrophilic nonwoven fabric was washed in an ethanol solution to remove impurities and contaminants from the fabric surface and interior. The washed hydrophilic nonwoven fabric was fixed on a roller collector as a substrate, and electrospinning was performed on the substrate using the aforementioned spinning solution at a spinning needle flow rate of 0.8 mL·h. -1 The distance between the needle and the collector was 15cm, and the working voltage was 16kV, resulting in a PAN / HMO nanofiber-based lithium ion sieve (LS).

[0080] Comparative Example 2

[0081] A method for preparing a PAN / HMO nanofiber-based lithium ion sieve (LS) is basically the same as that for Comparative Example 1, except that the PAN content in the spinning solution is 7 wt%.

[0082] Comparative Example 3

[0083] A method for preparing a PAN / HMO nanofiber-based lithium ion sieve (LS) is basically the same as that for Comparative Example 1, except that the PAN content in the spinning solution is 8 wt%.

[0084] Comparative Example 4

[0085] A method for preparing a PAN / HMO nanofiber-based lithium ion sieve (LS) is basically the same as that for Comparative Example 1, except that the PAN content in the spinning solution is 9 wt%.

[0086] Comparative Example 5

[0087] A method for preparing a PAN / HMO nanofiber-based lithium ion sieve (LS) is basically the same as that for Comparative Example 1, except that the PAN content in the spinning solution is 10 wt%.

[0088] Comparative Example 6

[0089] A method for preparing a PAN / HMO nanofiber-based lithium ion sieve (LS) is basically the same as that for Comparative Example 1, except that the PAN content in the spinning solution is 11 wt%.

[0090] Comparative Example 7

[0091] A method for preparing a PAN / HMO nanofiber-based lithium-ion sieve (LS) includes the following steps:

[0092] HMO particles were dispersed in a PAN solution (solvent: DMF) to obtain a spinning solution containing 8 wt% PAN and 6 wt% HMO particles. Commercial hydrophilic nonwoven fabric was washed in an ethanol solution to remove impurities and contaminants from the fabric surface and interior. The washed hydrophilic nonwoven fabric was then fixed onto a roller collector as a substrate, and electrospinning was performed on the substrate using the aforementioned spinning solution at a spinning needle flow rate of 0.8 mL·h. -1 The distance between the needle and the collector was 15cm, and the working voltage was 16kV, resulting in a PAN / HMO nanofiber-based lithium ion sieve (LS).

[0093] Comparative Example 8

[0094] A method for preparing a PAN / HMO nanofiber-based lithium ion sieve (LS) is basically the same as that for Comparative Example 7, except that the content of HMO particles in the spinning solution is 7 wt%.

[0095] Comparative Example 9

[0096] A method for preparing a PAN / HMO nanofiber-based lithium ion sieve (LS) is basically the same as that for Comparative Example 7, except that the content of HMO particles in the spinning solution is 8 wt%.

[0097] Comparative Example 10

[0098] A method for preparing a PAN / HMO nanofiber-based lithium ion sieve (LS) is basically the same as that for Comparative Example 7, except that the content of HMO particles in the spinning solution is 9 wt%.

[0099] Comparative Example 11

[0100] A method for preparing a PAN / HMO nanofiber-based lithium ion sieve (LS) is basically the same as that for Comparative Example 7, except that the content of HMO particles in the spinning solution is 10 wt%.

[0101] Comparative Example 12

[0102] A method for preparing a PAN / HMO nanofiber-based lithium ion sieve (LS) is basically the same as that for Comparative Example 7, except that the content of HMO particles in the spinning solution is 12 wt%.

[0103] Comparative Example 13

[0104] A method for preparing a Na2CO3 / cellulose acetate composite nanofiber-based base-activated lithium-ion sieve (ALS1) includes the following steps:

[0105] (1) Na₂CO₃ was dissolved in a CA solution (solvents were acetone and N,N-dimethylacetamide, mass ratio 2:1) to obtain a spinning solution, wherein the concentration of Na₂CO₃ in the spinning solution was 3 wt%. Commercial hydrophilic nonwoven fabric was washed in an ethanol solution to remove impurities and contaminants from the fabric surface and interior. The washed hydrophilic nonwoven fabric was fixed on a roller collector as a substrate, and electrospinning was performed on the hydrophilic nonwoven fabric substrate using the spinning solution at a spinning needle flow rate of 1.2 mL·h. -1 The distance between the needle and the collector is 15cm, the working voltage is 14kV, and a pre-alkalization layer is formed.

[0106] (2) HMO particles were dispersed in a PAN solution (solvent: DMF) to obtain an electrospinning solution. The PAN content in the electrospinning solution was 8 wt%, and the HMO particle content was 11 wt%. Electrospinning was performed on the pre-alkalized layer using the electrospinning solution at a spinning needle flow rate of 0.8 mL·h. -1 The distance between the needle and the collector was 15cm, and the working voltage was 16kV. A PAN / HMO nanofiber-based lithium ion sieve was obtained and named ALS1.

[0107] Comparative Example 14

[0108] A method for preparing a Na2CO3 / cellulose acetate composite nanofiber base-activated lithium ion sieve (ALS2) is basically the same as that of Comparative Example 13, except that in step (1), the concentration of Na2CO3 in the spinning solution is 6wt%.

[0109] Comparative Example 15

[0110] A method for preparing a Na2CO3 / cellulose acetate composite nanofiber base-activated lithium ion sieve (ALS3) is basically the same as that of Comparative Example 13, except that in step (1), the concentration of Na2CO3 in the spinning solution is 9wt%.

[0111] Comparative Example 16

[0112] A method for preparing a Na2CO3 / cellulose acetate composite nanofiber base-activated lithium ion sieve (ALS4) is basically the same as that of Comparative Example 13, except that in step (1), the concentration of Na2CO3 in the spinning solution is 12wt%.

[0113] Comparative Example 17

[0114] A method for preparing a Na2CO3 / cellulose acetate composite nanofiber base-activated lithium ion sieve (ALS5) is basically the same as that of Comparative Example 13, except that in step (1), the concentration of Na2CO3 in the spinning solution is 15wt%.

[0115] Comparative Example 18

[0116] A method for preparing a Na2CO3 / cellulose acetate composite nanofiber base-activated lithium ion sieve (ALS6) is basically the same as that of Comparative Example 13, except that in step (1), the concentration of Na2CO3 in the spinning solution is 18wt%.

[0117] Comparative Example 19

[0118] A method for preparing a nanofiber-based photothermal lithium-ion sieve includes the following steps:

[0119] (1) Na₂CO₃ was dissolved in a CA solution (solvents were acetone and N,N-dimethylacetamide, mass ratio 2:1, CA concentration 14 wt%) to obtain a spinning solution, wherein the concentration of Na₂CO₃ in the spinning solution was 12 wt%. Commercial hydrophilic nonwoven fabric was washed in an ethanol solution to remove impurities and contaminants from the fabric surface and interior. The washed hydrophilic nonwoven fabric was fixed on a roller collector as a substrate, and electrospinning was performed on the hydrophilic nonwoven fabric substrate using the spinning solution at a spinning needle flow rate of 1.2 mL·h. -1 The distance between the needle and the collector is 15cm, the working voltage is 14kV, and a pre-alkalization layer is formed.

[0120] (2) HMO particles and CB were dispersed in a PAN solution (solvent: DMF) to obtain a spinning solution. The PAN content in the spinning solution was 8 wt%, the HMO particle content was 11 wt%, and the CB content was 1 wt%. 3 mL of the spinning solution was placed in a syringe, and the propulsion rate of the spinning solution was 0.8 mL·h. -1The distance between the needle and the collector is 15cm, the working voltage is 16kV, and a photothermal lithium extraction layer is formed.

[0121] (3) The photothermal lithium extraction layer is covered on the pre-alkalization layer on the hydrophilic nonwoven fabric substrate to obtain the nanofiber-based photothermal lithium ion sieve.

[0122] Comparative Example 20

[0123] A method for preparing a nanofiber-based photothermal lithium-ion sieve includes the following steps:

[0124] (1) Na₂CO₃ was dissolved in a CA solution (solvents were acetone and N,N-dimethylacetamide, mass ratio 2:1, CA concentration 14 wt%) to obtain a spinning solution, wherein the concentration of Na₂CO₃ in the spinning solution was 12 wt%. Commercial hydrophilic nonwoven fabric was washed in an ethanol solution to remove impurities and contaminants from the fabric surface and interior. The washed hydrophilic nonwoven fabric was fixed on a roller collector as a substrate, and electrospinning was performed on the hydrophilic nonwoven fabric substrate using the spinning solution at a spinning needle flow rate of 1.2 mL·h. -1 The distance between the needle and the collector is 15cm, the working voltage is 14kV, and a pre-alkalization layer is formed.

[0125] (2) HMO particles were dispersed in PAN solution A (solvent: DMF) to obtain spinning solution A, in which the content of PAN in spinning solution A was 8 wt% and the content of HMO particles in spinning solution A was 11 wt%; CB was dispersed in PAN solution B (solvent: DMF) to obtain spinning solution B, in which the content of CB in spinning solution B was 1 wt%; 3 mL of each of spinning solution A and spinning solution B were placed in a coaxially connected syringe, and coaxial electrospinning was performed with spinning solution B as the sheath spinning solution and spinning solution A as the core spinning solution. The propulsion rate of the sheath spinning solution was 0.8 mL·h. -1 The propulsion rate of the core spinning solution is 0.75 mL·h. -1 The distance between the coaxial needle and the collector is 15cm, and the working voltage is 16kV, forming a photothermal lithium extraction layer with a core-sheath structure.

[0126] (3) The photothermal lithium extraction layer is covered on the pre-alkalization layer on the hydrophilic nonwoven fabric substrate to obtain the nanofiber-based photothermal lithium ion sieve.

[0127] Test Example 1

[0128] The lithium extraction performance of LS with different PAN and HMO particle contents was tested in Comparative Examples 1-12. The test method was to place the LS into Li + Li adsorption in a lithium-containing solution with a concentration of 50 mg / L +The adsorption was carried out in a constant temperature shaker at 25℃ and 100rpm for 24 hours, and the test results are as follows. Figure 2 and Figure 3 As shown.

[0129] from Figure 2 As can be seen, when the PAN content in the spinning solution is 6, 7, 8, 9, 10, and 11 wt% (at which point the HMO particle content is 11 wt%), the lithium-ion adsorption capacities of LS are 9.22, 12.17, 13.23, 10.19, 8.16, and 6.33 mg·g, respectively. -1 The results showed that with increasing PAN content, LS had a greater effect on Li. + The adsorption capacity of LS showed a trend of first increasing and then decreasing. Specifically, in the initial stage with low PAN content, the viscosity of the spinning solution was low, which prevented HMO particles from stably adhering to the inside and surface of the fiber, resulting in a low adsorption capacity. When the PAN content was 8 wt%, the adsorption capacity of LS reached its maximum value of 13.23 mg·g. -1 Subsequently, as the PAN content continued to increase, the HMO particles were severely encapsulated by the excessive PAN, limiting their distribution to only localized areas and making it difficult for them to interact with Li in the solution. + Sufficient contact leads to a decrease in lithium extraction performance. Therefore, controlling the PAN content in LS is a key factor in improving the overall adsorption capacity. Thus, LS with a PAN content of 8 wt% was selected to further investigate the effect of different HMO contents on its lithium adsorption capacity.

[0130] from Figure 3 As can be seen, the effect of HMO particle content on LS adsorption capacity shows a "first increase, then decrease" trend. Specifically, in the stage of low HMO particle loading, as its content increases, more HMO particles can be uniformly dispersed and exposed inside and on the surface of the fiber, thus enhancing the adsorption capacity of Li in the solution. + Contact with HMO particles provides more reaction sites, thus increasing the adsorption capacity; when the HMO particle content is 11 wt%, the lithium extraction performance of LS reaches its peak at 13.23 mg·g⁻¹. -1 However, when the HMO particle content exceeded 12 wt%, the lithium extraction performance of LS actually decreased. This may be because when the HMO particle loading is too high, the loading inside and on the surface of the fiber reaches saturation, and excess HMO particles are prone to agglomeration or detachment, making it difficult for effective reaction sites to react with Li. + Sufficient contact is crucial. Therefore, controlling the loading of HMO particles in the PAN / HMO nanofiber-based lithium-ion sieve is also key to improving the overall adsorption capacity.

[0131] In summary, the prepared PAN / HMO nanofiber-based lithium ion sieve extraction performance is optimal when the PAN content in the spinning solution is 8 wt% and the HMO particle content is 11 wt%.

[0132] Test Example 2

[0133] The pH adjustment performance and lithium adsorption performance of LS (Comparative Example 3) and Na2CO3 / cellulose acetate composite nanofiber-based alkaline activated lithium ion sieves (ALS) with different Na2CO3 contents in Comparative Examples 13-18 were tested by placing ALS in deionized water.

[0134] ALS can achieve alkaline activation at the adsorption interface. Its internally interconnected hydrophilic channels can form directional capillary flow, effectively promoting water circulation and ion interactions. As a strong electrolyte, Na₂CO₃ rapidly dissociates in aqueous media, first forming a transient NaHCO₃ intermediate and some OH⁻. - Subsequently, a large amount of OH- is generated through a hydrolysis reaction. - This creates a stable alkaline interfacial environment for lithium extraction from HMO. By controlling the amount of Na2CO3 incorporated and the nanofiber network structure, the interfacial alkalinity can be precisely adjusted, such as... Figure 4 As shown in Figure a.

[0135] Test results showed that the initial pH of the deionized water was 6.9. As the Na₂CO₃ concentration increased, the pH rose rapidly in the initial stage; when the Na₂CO₃ concentration reached 12 wt%, the pH of the deionized water rose to 11.4. Further observation revealed that as the Na₂CO₃ content increased from 0 to 18 wt%, the pH of the deionized water showed a gradual upward trend. Furthermore, when the Na₂CO₃ content reached 12 wt% (i.e., ALS₃), the pH value remained essentially unchanged after rising from the initial 6.9 to 11.5. This indicates a positive correlation between Na₂CO₃ content and solution pH.

[0136] Furthermore, lithium brine exhibits a metastable dissolution equilibrium in the high-salt environment formed by Na₂CO₃. Ion interactions compress the electric double layer around Na₂CO₃ particles through the Debye shielding effect, weakening Coulomb forces and forming local concentration gradients. Therefore, under strong alkaline activity, the adsorption kinetics of ALS are significantly accelerated, and the adsorption capacity is effectively enhanced, such as... Figure 4 As shown in b.

[0137] Test Example 3

[0138] The solar absorbance of PAN nanofibers, ALS4 (Comparative Example 16), and the multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieves of Examples 1-5 in the 250-2500 nm range was measured using a UV-IR-Vis spectrometer (UV3600). The PAN nanofibers were prepared by washing commercial hydrophilic nonwoven fabric in an ethanol solution to remove impurities and contaminants from the fabric surface and interior. The washed hydrophilic nonwoven fabric was then fixed onto a roller collector as a substrate. Electrospinning was performed on the hydrophilic nonwoven fabric substrate using a PAN solution (DMF solvent, PAN content 8 wt%) at a spinning needle flow rate of 0.8 mL·h. -1 The distance between the needle and the collector was 15cm, and the working voltage was 16kV, resulting in PAN nanofibers.

[0139] Test results are as follows Figure 5 As shown, without the loading of photothermal nanoparticles CB, the full-spectrum solar energy absorption capacity of PAN nanofibers is weak; when only HMO is loaded, the overall solar energy absorption performance of ALS is not improved, and the absorption capacity remains at a low level; while the light absorption rate of APLS3 (with 11 wt% HMO particles in spinning solution A and 1 wt% CB content in spinning solution B) can reach over 90%. This is because under the action of solar radiation, electrons in CB nanoparticles are excited to higher energy levels, then relax through non-radiative transitions and release heat in the form of lattice vibrations, thereby significantly enhancing the absorption capacity of solar energy.

[0140] Test Example 4

[0141] The lithium adsorption performance of multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieves with different CB contents in Examples 1-5, LS in Comparative Example 3, and nanofiber-based photothermal lithium-ion sieves in Comparative Examples 19 and 20 under dark and light conditions (1 sun) was tested. The test method was as follows:

[0142] Dark conditions: Different lithium ion sieves were placed in 40 mL of Li + The solution was prepared in a lithium-containing solution with a concentration of 100 mg / L, and then transferred to a constant-temperature shaker at 25°C and 100 rpm for 6 hours.

[0143] Irradiation conditions: Different lithium-ion sieves were placed on suspended insulating foam and then placed in a beaker, where the Li in the solution... + The concentration is 100 mg / L, and a water-guiding cloth strip is connected. The beaker is wrapped with heat-insulating foam to prevent heat loss and placed under a xenon lamp at room temperature to simulate real sunlight, with a light intensity of 1 kW / m². 2 (i.e., 1 sun), the test duration is 6 hours.

[0144] Test results are as follows Figure 6 and Figure 7As shown, with the increase of CB content, photothermal nanoparticles are uniformly distributed on the surface of nanofibers, which is beneficial to enhancing solar energy absorption and interfacial evaporation. However, excessive CB coverage on the surface reduces the accessible HMO active sites. Excessive CB will adversely affect lithium adsorption under any radiation conditions. Under illumination, the adsorption capacity of APLS shows a "first increase, then decrease" trend with increasing CB content: initially, increasing CB content can improve the light absorption performance of APLS, promote photothermal conversion efficiency and ion enrichment, thereby enhancing the adsorption effect; however, when the CB content is too high, its excessive coverage on the surface reduces the accessible HMO sites, leading to a decrease in the lithium extraction performance of APLS.

[0145] Under illumination (1 sun), compared with the nanofiber-based photothermal lithium-ion sieves with the hybrid core-sheath structure of Comparative Example 19 and Comparative Example 20, the APLS3 of Example 3 with the core CB / sheath HMO structure can promote lithium extraction through photothermal evaporation and avoid the performance limitations caused by particle aggregation, thus exhibiting superior lithium extraction performance.

[0146] Test Example 5

[0147] An indoor photothermal lithium extraction experiment was conducted on APLS3 from Example 3. The experiment was performed at room temperature. + The content is 250 mg·L -1 The adsorption was carried out in a lithium-containing solution for 6 hours.

[0148] Test results are as follows Figure 8 As shown in Figure a, when the light intensity increases from 0.8 sun to 2.0 sun, the adsorption kinetic constant (0.061-0.078 g·mg) changes. -1 ·h -1 The change confirmed the increase in equilibrium adsorption capacity (22.91 mg·g). -1 -42.01 mg·g -1 The results showed that the adsorption capacity increased significantly with increasing light intensity, indicating that the lithium-ion sieve possesses excellent thermodynamic adsorption performance and is suitable for long-term continuous adsorption processes. The adsorption of lithium by APLS3 is a typical endothermic reaction; under enhanced radiation conditions, increased photothermal input promotes Li adsorption. + Migration and interaction with ion sieves.

[0149] Under different temperatures and with and without light (same as the test conditions in Test Example 4, except that the Li in the lithium-containing solution...), + The content is 250 mg·L -1 The adsorption capacity of APLS3 is as follows: Figure 8As shown in Figure b, the correspondence between light intensity and temperature is as follows: 0.8 sun corresponds to 25℃, 1.2 sun corresponds to 30℃, 1.6 sun corresponds to 35℃, and 2.0 sun corresponds to 40℃. The results show that the adsorption capacity is significantly higher under light conditions: at 25℃, the adsorption capacity of APLS3 under light conditions is 22.91 mg·g⁻¹. -1 The level increased by 6.3 mg / g compared to the absence of light. -1 At 40℃, the increase reached 11.48 mg·g. -1 The adsorption capacity is as high as 42.01 mg·g. -1 This indicates that interfacial water evaporation can promote ion transport and enrichment, while photothermal drive can further enhance its adsorption performance.

[0150] Figure 8 Figure c shows the cycling performance of APLS3. The APLS3, saturated with adsorption, was acid-washed in a 0.3 mol / L hydrochloric acid solution for 24 h to allow the adsorbed Li to... + Desorption was performed using an ICP spectrometer to test the initial and stable values ​​of the solution after adsorption, and then calculated according to the formula. The test results show that after multiple cycles, the adsorption capacity of APLS3 can still be maintained at a high level, especially after 10 cycles, only a slight decrease is observed, proving that the APLS of the present invention has excellent cycling stability.

[0151] Test Example 6

[0152] Photothermal lithium extraction experiments were conducted on APLS3 from Example 3 in real Qinghai Emerald Salt Lake water. ICP-OES was used to measure the Li content in the Qinghai Emerald Salt Lake water. + Na + K + Ca 2+ Mg 2+ The contents were 95.42, 4814.57, 5380.68, 119.14, and 53820.05 mg·L, respectively. -1 APLS3 was placed in the water of Qinghai Emerald Salt Lake for 6 hours under conditions of no light and in a constant temperature vibrator at 25°C for adsorption. The test results are as follows: Figure 9 As shown, APLS3 exhibits excellent lithium extraction performance when treating complex saline lake water containing a large number of competing ions—its lithium adsorption capacity can reach 15.99 mg·g⁻¹. -1 Furthermore, it has extremely low adsorption capacity for other ions such as sodium, potassium, calcium, and magnesium.

[0153] Calculations show that, under solar radiation conditions, the separation coefficients of APLS3 for lithium ions and the aforementioned competing ions are: sodium ions 695.55, potassium ions 739.6, calcium ions 19.65, and magnesium ions 6248.38, which fully demonstrates its excellent ion selectivity.

[0154] In summary, the multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve provided by this invention adopts a multi-level scale structural design. By integrating a microporous capillary network with functionalized nanoparticles, it achieves synergistic enhancement of directional brine transport and selective lithium adsorption. Its core components and technical features are as follows: A hydrophilic fabric serves as the substrate, combining water transport channels and structural support functions; it integrates alkaline sodium carbonate (Na₂CO₃) as a pH-regulating active substance, carbon black (CB) as a photothermal conversion material, and a lithium-ion sieve (HMO) loaded on nanofibers as the core component for lithium capture. The nanofibers themselves possess a high specific surface area and abundant interfiber gaps, providing favorable conditions for ion transport and water circulation.

[0155] This invention provides a multi-layer pre-alkalized nanofiber-based photothermal lithium-ion sieve. Utilizing nanofiber engineering, it endows the ion sieve with high cycling stability. Simultaneously, it employs a confined alkali activity online control technology constructed through a nanofiber network, achieving precise regulation of the interfacial alkaline environment. A core-sheath nanofiber design is used to construct a photothermal evaporation-driven ion enrichment system, combined with a selective adsorption mechanism to enhance the targeted capture of lithium ions. This forms an ion sieve structure system with synergistic effects of alkali activation and photothermal effects. Through the synergistic regulation of these two aspects, lithium extraction efficiency and selectivity are comprehensively improved. This invention, through the integration of multi-level structures and functions, achieves the integration of brine transport, alkalinity regulation, photothermal conversion, ion enrichment, and selective adsorption, providing an innovative solution for efficient lithium extraction.

[0156] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve, characterized in that, Includes the following steps: (1) Dissolve an alkaline salt in a cellulose acetate solution to obtain a spinning solution, and use the spinning solution to perform electrospinning on a hydrophilic fabric substrate to form a pre-alkalized layer. (2) H 1.6 Mn 1.6 O4 particles are dispersed in polyacrylonitrile solution A to obtain spinning solution A, and photothermal nanoparticles are dispersed in polyacrylonitrile solution B to obtain spinning solution B. Coaxial electrospinning is performed using spinning solution A as the sheath spinning solution and spinning solution B as the core spinning solution to form a photothermal lithium extraction layer with a core-sheath structure. (3) The photothermal lithium extraction layer is covered on the pre-alkalization layer on the hydrophilic fabric substrate to obtain the multilayer pre-alkalized nanofiber-based photothermal lithium ion sieve.

2. The preparation method according to claim 1, characterized in that, In step (1), the concentration of the alkaline salt in the spinning solution is 3-18 wt%.

3. The preparation method according to claim 1, characterized in that, In step (1), the electrospinning process parameters include: a spinning needle flow rate of 1.0-1.4 mL·h. -1 The distance between the needle and the collector is 14-16cm, and the operating voltage is 13-15kV.

4. The preparation method according to claim 1, characterized in that, In step (2), the H 1.6 Mn 1.6 The preparation method of O4 particles includes the following steps: mixing lithium source and manganese source, followed by hydrothermal reaction and calcination to obtain a precursor, and then acid washing the precursor to obtain the H. 1.6 Mn 1.6 O4 particles.

5. The preparation method according to claim 1, characterized in that, In step (2), the PAN content in the spinning solution A is 6-11 wt%.

6. The preparation method according to claim 1, characterized in that, In step (2), H in the spinning solution A 1.6 Mn 1.6 The content of O4 particles is 6-14 wt%.

7. The preparation method according to claim 1, characterized in that, In step (2), the content of photothermal nanoparticles in the spinning solution B is 1-5 wt%.

8. The preparation method according to claim 1, characterized in that, In step (2), the process parameters for coaxial electrospinning include: the propulsion rate of the sheath spinning solution is 0.7-0.9 mL·h. -1 The propulsion rate of the core spinning solution is 0.7-0.8 mL·h. -1 The distance between the coaxial needle and the collector is 14-16cm, and the operating voltage is 15-17kV.

9. A multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve prepared by the preparation method according to any one of claims 1-8.

10. The application of the multilayer pre-alkalized nanofiber-based photothermal lithium-ion sieve of claim 9 in lithium extraction from salt lakes.

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