A photothermal material for efficient lithium-magnesium separation, its preparation method and application

Abstract

This invention belongs to the field of solar energy resource utilization and lithium extraction from salt lakes, specifically relating to a photothermal material for efficient lithium-magnesium separation, its preparation method, and its applications. The photothermal material PM of this invention comprises a selective layer PM. SL and photothermal layer PM EDL Under sunlight, the photothermal layer PM EDL The absorption of light energy generates heat, driving the continuous evaporation of water at the interface, causing ions in the solution to accumulate at the evaporation interface, while the selective layer PM... SL Its nanochannel structure and surface charge interaction enable the selective separation of magnesium and lithium, thereby achieving efficient enrichment of lithium ions in lithium-containing brine, which has good application prospects in the field of lithium extraction from salt lake brine.

Description

Technical Field

[0001] This invention belongs to the field of solar energy resource utilization and lithium extraction from salt lakes, specifically relating to a photothermal material for efficient lithium-magnesium separation, its preparation method, and its application. Background Technology

[0002] Lithium, known as "white oil," holds a crucial strategic position in the field of new energy materials and is a key raw material for lithium-ion battery production. In recent years, with the rapid development of new energy vehicles, electronic devices, and high-power energy storage technologies, global demand for lithium resources has increased dramatically, projected to grow 8 to 10 times by 2050. This makes efficient, low-consumption, and sustainable lithium resource extraction extremely important. Salt lake brines, as the primary source of recoverable lithium on land, account for approximately 70% of global reserves. Compared to lithium extraction from ore, brine resources are more abundant and have lower extraction costs. Therefore, direct lithium extraction from salt lake brines has become a key approach to ensuring a secure supply of lithium resources to meet rapidly growing demand.

[0003] To effectively address the lithium shortage, exploring innovative approaches to lithium extraction is crucial, particularly the extraction of lithium from low-quality brine, i.e., Li. + Brine with a concentration <260 ppm or a magnesium-to-lithium mass ratio greater than 6.15 has vast untapped reserves that could significantly alleviate supply issues. Traditional lithium extraction evaporation-precipitation methods suffer from inefficiency in low-quality brine. While direct lithium extraction technologies such as solvent extraction, adsorption, membrane separation, and electrochemical separation can effectively extract lithium resources directly from raw brine, these technologies have high energy consumption and costs, complex infrastructure, and release large amounts of greenhouse gases during energy consumption, causing significant environmental impact. These drawbacks hinder the practical application of current lithium extraction technologies in salt lake regions.

[0004] Solar-enhanced lithium extraction (SELE) utilizes photothermal materials to absorb sunlight at the interface and convert it into localized heat, inducing a phase change evaporation of water to produce clean water while simultaneously separating salt ions. Unlike traditional heating methods, SELE minimizes heat loss to the surrounding environment and enables rapid phase change evaporation directly on the surface, generating vapor while leaving behind Li₂. + During evaporation, dissolved interfering salts (such as Mg) 2+ ) and Li + In a brine solution, these ions become increasingly concentrated, and as the water continues to evaporate, they eventually reach supersaturation, thus achieving the desired concentration of Li in the brine lake. + Selective collection. Compared to traditional solar evaporation ponds, SELE offers faster processing speeds, smaller footprint, and higher Li-weighted energy efficiency. +Production. Processing time has been drastically reduced from a year to days or weeks, solving the Li... + This approach addresses key bottlenecks in the supply chain and improves production flexibility. It offers significant advantages in energy efficiency, carbon footprint reduction, and operational sustainability, making it particularly well-suited for addressing the global challenge of water scarcity. However, SELE still faces the following challenges: 1) The salt water contains a large number of interfering ions, which will affect Li + The extraction efficiency and stability are affected. Working in high-concentration brine often leads to salt scaling, which not only clogs water transport channels but also reduces the light absorption and photothermal conversion efficiency of the photothermal material. Li recovery... + Acid washing is required, which inevitably damages the photothermal material and affects its long-term cycling performance.

[0005] 2) Li + The selective separation of photothermal materials is limited by the separation capability of membrane separation technology; therefore, it is necessary to prepare Li with high selectivity and durability. + / Mg 2+ Separation membrane. For Li+ selectively separated photothermal materials that crystallize directly at the photothermal interface, crystallization affects light absorption and photothermal conversion efficiency, leading to poor long-term stability of the design. When using inorganic materials as Li... + In the photothermal material of the storage layer, the low water evaporation rate and layered design hinder the Li + Transportation during the evaporation process. Using hydrogel-based Li + In the photothermal material of the storage layer, Li + Recovery requires soaking, but this does not guarantee complete recovery of Li from the storage layer. + Furthermore, the non-integrated design significantly limits mass transfer during the SELE process, necessitating structural improvements to enhance Li. + Extraction rate.

[0006] Li in photothermal enhanced lithium extraction + Insufficient selectivity, Li + Problems such as insufficient extraction rate and insufficient durability necessitate the development of a method that combines high Li- content with high efficiency. + Selectivity, high Li + Flux and controllable Li + Photothermal materials with enrichment and desorption capabilities enable the production of high-purity lithium salts. Summary of the Invention

[0007] The purpose of this invention is to provide a photothermal material for efficient lithium-magnesium separation, its preparation method, and its applications. This invention improves existing interfacial polymerization techniques to obtain Li-magnesium materials with high selectivity. + Separation layer, and simultaneously using temperature-sensitive hydrogel as photothermal layer to construct Li +A transport pathway is established to achieve the production of high-purity lithium salts. This invention achieves the above objective through the following technical solution: A method for preparing a photothermal material for efficient lithium-magnesium separation includes the following steps: Step 1: A polyamide layer is polymerized at the interface of the substrate film material with an aqueous solution of quaternized polyethyleneimine and a solution of trimesoyl chloride to obtain a layer with Mg 2+ / Li + Selective screening function selection layer PM SL ; Step 2: Temperature-sensitive monomers, trehalose, cross-linking agents, and initiators are applied to the selective layer PM. SL A thermosensitive hydrogel is formed on the back side via free radical polymerization. Then, a light absorber is added to the surface of the thermosensitive hydrogel via in-situ polymerization or physical mixing, thereby selectively absorbing PM... SL Photothermal layer PM introduced on the back EDL This yields a photothermal material for efficient lithium-magnesium separation.

[0008] In some embodiments, in step 1, the quaternized polyethyleneimine is prepared by modifying polyethyleneimine with a haloamine or a haloamine salt to obtain quaternized polyethyleneimine. The temperature of the above reaction is 50~100℃ and the reaction time is 5~15h; The mass ratio of haloamine or haloamine salt to polyethyleneimine is 1: (5~20); The structural formula of the haloamine is: X-(CH2) m -NH2, where X is F, Cl, Br, I, and m is 1, 2, 3, 4, 5, or 6; Preferably, the haloamine salt is 2-bromoethylamine hydrobromide or 2-bromoethylamine hydrochloride.

[0009] In some embodiments, in step 1, the concentration of the quaternized polyethyleneimine (QPEI) aqueous solution is 0.5-5 wt%; the concentration of the trimesoyl chloride solution is 0.1-1 wt%; and the solvent of the trimesoyl chloride solution is selected from one or more of n-heptane, n-hexane, dichloromethane, trichloromethane, tetrahydrofuran, acetone, ethyl acetate, methanol, ethanol, DMSO and DMF, preferably n-heptane.

[0010] In some embodiments, in step 1, trimesoyl chloride is dissolved in n-heptane to obtain a TMC solution as the oil phase. Interfacial polymerization of QPEI as the aqueous phase solution and TMC as the oil phase solution is performed on an rGO substrate to obtain PM. SL ; Preferably, the rGO film is immersed in a QPEI aqueous solution. The film is then removed and the excess aqueous solution on its surface is wiped off with a roller, ensuring the aqueous solution is evenly distributed across the film surface. The rGO / QPEI film is placed in a mold, and a certain amount of TMC solution is poured into the mold. At this point, QPEI and TMC react at the water-oil interface (rGO film surface) to form a polyamide film. After the reaction, the TMC solution is poured out, and the film is transferred to an oven. The film is then removed and immersed in deionized water to remove residual solution, yielding PM. SL .

[0011] In some implementations, in step 1, the substrate film material is a reduced graphene oxide film, a graphene oxide film, a carbon nanotube film, or a Ti3C2T film. X MXene membrane.

[0012] In some embodiments, the substrate membrane material is a reduced graphene oxide (rGO) membrane, and its preparation method includes the following steps: Using polytetrafluoroethylene, nylon-6, or nylon-66 as filter membranes, the graphene oxide dispersion is filtered to form a graphene oxide membrane, which is then partially reduced by ultraviolet light irradiation to obtain a reduced graphene oxide membrane. In some implementation schemes, the duration of ultraviolet light irradiation is 0.5 to 5 hours; In some embodiments, the concentration of the graphene oxide dispersion is 0.05–0.5 mg / mL. -1 .

[0013] In some embodiments, the thermosensitive monomer is selected from one or more of N-isopropylacrylamide, N-vinylcaprolactam, polyethylene glycol methyl ether methacrylate, 2-(2-methoxyethoxy)ethyl methacrylate, N-vinylpyrrolidone, hydroxypropyl acrylate, N-hydroxyethylacrylamide, N-hydroxypropylacrylamide, and N-isobutylacrylamide. In some embodiments, the crosslinking agent is selected from one or more of ethylene glycol dimethacrylate (EGDMA), polyethylene glycol diacrylate (PEGDA), N,N'-methylenebisacrylamide (MBAA), pentaerythritol tetraacrylate (PETTA), 1,3-butanediol dimethacrylate (BGDMA), 1,4-butanediol diacrylate (BDDA), 1,6-hexanediol diacrylate (HDDA), 1,6-hexanediol dimethacrylate (HDDMA), neopentyl glycol diacrylate (NPGDA), and trimethylolpropane triacrylate (TMPTA), preferably N,N'-methylenebisacrylamide; In some embodiments, the initiator is a mixture of ammonium persulfate and sodium bisulfite, a mixture of ammonium persulfate and sodium bisulfite, a mixture of sodium persulfate and sodium bisulfite, a mixture of potassium persulfate and sodium bisulfite, a mixture of sodium persulfate and sodium bisulfite, a mixture of potassium persulfate and sodium bisulfite, a mixture of potassium persulfate and tetramethylethylenediamine, a mixture of ammonium persulfate and tetramethylethylenediamine, or a mixture of sodium persulfate and tetramethylethylenediamine. In some embodiments, the mass ratio of the thermosensitive monomer to trehalose is (2~10):1.

[0014] In some embodiments, the light absorber is selected from one or more of carbon black, activated carbon, graphene oxide, carbon nanotubes, Mxene, and polypyrrole; Preferably, the light absorber is polypyrrole; the polypyrrole is added to the surface of the thermosensitive hydrogel by in-situ polymerization; preferably, the polymerizing monomer is pyrrole with a concentration of 0.05~2 wt%; preferably, the initiator used for polymerization is selected from ammonium persulfate, potassium persulfate and sodium persulfate with a concentration of 0.05~2 wt%.

[0015] In some implementations, in step 2, a diffusion cell is used as the reaction carrier for polymerization. The diffusion cell consists of two independent chambers, upper and lower, separated by a selective layer PM. SL The system is separated and clamps are used to ensure its airtightness and stability. During operation, the PMSL is positioned between the two chambers, with the polyamide membrane facing down into the lower chamber and its back facing up into the upper chamber.

[0016] In some implementations, in step 2, the thermosensitive monomer and trehalose are dissolved in deionized water, centrifuged to remove bubbles after complete dissolution, and then the crosslinking agent and initiator are added and stirred thoroughly to obtain the precursor solution of the hydrogel. In some embodiments, a precursor solution for the hydrogel is poured into the upper chamber, where it undergoes free radical polymerization at room temperature to obtain a hydrogel with an unswollen hydrogel thickness of 2-5 mm. The remaining precursor solution is then poured out, and deionized water is added to the upper chamber to fully immerse the hydrogel, resulting in a swollen hydrogel with a thickness of 6-12 mm, preferably 8 mm. The deionized water is then poured out, and a pyrrole solution is added to the upper chamber to fully immerse the swollen hydrogel for 20-30 hours. The remaining pyrrole solution is then poured out, and an initiator solution is added to fully immerse the hydrogel for 0.5-5 hours, initiating in-situ polymerization of pyrrole on the hydrogel surface to form polypyrrole. The remaining initiator solution is then poured out, allowing the selected PM layer to be polymerized. SL A black photothermal layer PM is introduced on the back. EDL .

[0017] On the other hand, the present invention also protects a photothermal material for efficient lithium-magnesium separation, said photothermal material being prepared by the above method.

[0018] On the other hand, the present invention also protects the application of the above-mentioned photothermal materials in lithium extraction from salt lakes or seawater.

[0019] Compared with the prior art, the present invention achieves the following beneficial effects: (1) By constructing a polyamide selective layer on the surface of the substrate membrane material using interfacial polymerization and introducing quaternized polyethyleneimine as an aqueous monomer, the composite membrane surface is given a positive charge, thereby controlling the surface charge properties and nanochannel structure of the membrane and achieving the desired control of Mg. 2+ With Li + Selective transmission.

[0020] (2) By introducing photothermal components into a thermosensitive hydrogel system containing trehalose, a hydrogel material with good photothermal conversion performance and porous structure is prepared, which can efficiently absorb light energy and promote interfacial evaporation under sunlight, while achieving local enrichment of ions in the solution.

[0021] (3) The thermosensitive photothermal hydrogel enrichment layer and the composite membrane are integrated into one assembly. Under solar-driven conditions, the local concentration of lithium ions in the solution is enhanced by interfacial evaporation, and the selective transport characteristics of the composite membrane are utilized to achieve Mg 2+ With Li + Effective separation of lithium ions improves the enrichment efficiency of lithium ions in the brine system.

[0022] (4) The photothermal material of the present invention is available in 1 kW m -2 Under such irradiation intensity, the water evaporation rate reaches as high as 3.42 kg / h. -1 m -2 And Mg in the feed 2+ / Li + When the molar ratios are 1:1 and 20:1, separation factors of 36.46 and 80.25 are achieved, respectively, which are far higher than those of existing technologies. Attached Figure Description

[0023] Figure 1 Selecting layer PM for Example 1 SL A schematic diagram of its preparation.

[0024] Figure 2 This is a schematic diagram of the preparation of the photothermal material PM in Example 1.

[0025] Figure 3 The diagram and physical image show the diffusion cell of Example 1.

[0026] Figure 4 For PM SL and PMEDL A physical image of a double-layer PM (a), PM EDL Stress-strain tensile curves (b) and dynamic mechanical analysis (c) of PNIPAm / PPy hydrogel.

[0027] Figure 5 The images show the SEM and AFM correlation spectra of the photothermal material PM in Example 1.

[0028] Figure 6 For PNIPAm / PPy hydrogel and PM EDL The photothermal conversion performance of the polymer films is shown in the graphs, where (a) PNIPAm / PPy and PM EDL Absorption curves across the entire solar spectrum; (b) PNIPAAm / PPy and PMEDL in the range of 0.25 to 2 kW m -2 Surface temperature variation under illumination intensity; (c) PNIPAm / PPy and PM EDL Thickness variation under illumination intensity. (d) PM EDL Graph showing the volume change of water separated within 300 s; (e) PM EDL Photos of the objects before and after water was separated.

[0029] Figure 7 For PNIPAm / PPy hydrogel and PM EDL The correlation spectrum of the photothermal evaporation performance of polymer films, where (a) PM EDL (a) Schematic diagram of the aqueous state of PNIPAm / PPy hydrogel, red represents BW, yellow represents IW, and blue corresponds to FW; (b) Schematic diagram of the aqueous state of PNIPAm / PPy hydrogel; (c) Schematic diagram of PNIPAm / PPy and PM EDL saturated water content; (d) DSC analysis of PNIPAAm / PPy and PM EDL Melting behavior of bulk water and ice water; (e) Bulk water and PNIPAm / PPy / PM EDL Differential scanning calorimetry of the aqueous phase; (f) PNIPAAm / PPy and PM EDL Between 0.25 and 2 kW m -2 Evaporation rate under light intensity.

[0030] Figure 8 The graph shows the correlation between the photothermal lithium extraction performance of the photothermal material PM in Example 1. Detailed implementation method: The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The endpoints and any values ​​of the ranges described in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The raw materials and reagents used in the following examples are commercially available.

[0032] Preparation Example 1: Preparation of Graphene Oxide Dispersion Add 400 mL of concentrated sulfuric acid (98%) to a 1000 mL beaker and fix the beaker in an ice-water bath. Start mechanical stirring and add 16 g of natural flake graphite (200-1000 mesh) and 8 g of sodium nitrate in sequence. Continue stirring in the ice-water bath for 30 min, then slowly add 64 g of potassium permanganate to the above reaction system while ensuring that the temperature of the reaction system is always below 0℃. Then continue the reaction at this temperature for 2 h.

[0033] The reaction system was transferred to a 35°C constant temperature water bath and stirred for 30 min. Then, 600 mL of deionized water was added to the reaction system using a constant flow pump, initially slowly and gradually increasing the rate to ensure the reaction temperature did not exceed 40°C. The reaction system was then transferred to a 98°C constant temperature water bath and stirred for approximately 40 min until the system turned bright yellow. At this point, the reaction was stopped, and the resulting product was slowly poured into 1000 mL of deionized water. 80 mL of hydrogen peroxide (30%) was slowly added while stirring continuously until no more bubbles were generated. Finally, the reaction product was poured into a Buchner funnel and filtered while hot. The filter cake was washed three times with 300 mL of dilute hydrochloric acid (5%). The filter cake was then redispersed in 1000 mL of deionized water and placed in a dialysis bag (molecular weight cutoff, 8000~14000 Da) for dialysis until the conductivity of the dialysate decreased to 8 μS / cm. -1 The following steps involve centrifugation to remove impurities and concentration to obtain a graphene oxide dispersion.

[0034] Example 1 A method for preparing a photothermal material for efficient lithium-magnesium separation includes the following steps: Step 1: Add 10 mL of graphene oxide (GO) (0.1 mg / mL)-1 The dispersion was used as a substrate of Nylon 66 membrane. A GO film with a diameter of 45 mm was obtained by vacuum filtration, and then a partially reduced rGO film was obtained by UV irradiation for 1 hour. 2-Bromoethylamine hydrobromide, polyethyleneimine, and water were mixed at a mass ratio of 1:10:100 and stirred at 70 °C for 12 hours until homogeneous. The resulting solution was then diluted 10 times to obtain a 1.0 wt% QPEI aqueous solution. 0.1 g of trimesoyl chloride (TMC) was dissolved in 100 g of n-heptane to obtain a 0.1 wt% TMC solution as the oil phase.

[0035] The rGO film was completely immersed in a QPEI (quaternized polyethyleneimine) aqueous solution for 3 minutes. The rGO film was then removed, and excess aqueous solution was wiped off the surface with a roller to obtain an rGO / QPEI film. The rGO / QPEI film was then placed in a mold, and an appropriate amount of TMC solution was poured into the mold to completely submerge the rGO / QPEI film. QPEI and TMC reacted on the surface of the rGO film to form a polyamide film. After reacting for 1 minute, the TMC solution was poured out, and the film was transferred to an 80°C container. o After drying in an oven at C for 5 minutes, remove the membrane and immerse it in deionized water to remove residual solution, thus obtaining the membrane with Mg. 2+ / Li + Selective screening function selection layer PM SL .

[0036] Step 2: Add 1.0 g of N-isopropylacrylamide (NIPAm) monomer and 0.25 g of trehalose to a flat-bottomed glass test tube, and dissolve them in 6 mL of deionized water. After thorough dissolution, centrifuge to remove bubbles, and then add a 0.1 mol / L solution of the cross-linking agent N,N'-methylenebisacrylamide (MBAA). -1 120 μL of ammonium persulfate (APS) solution (0.1 mol / L) -1 700 μL of tetramethylethylenediamine (TEMED) and 24 μL of TEMED were mixed thoroughly to obtain a precursor solution for the hydrogel; A diffusion cell is used as the reaction carrier during polymerization. The diffusion cell consists of two independent chambers, upper and lower. SLBetween the two chambers, with the polyamide membrane facing down into the lower chamber and up into the upper chamber, 5 mL of the hydrogel precursor solution was poured into the upper chamber. The precursor solution underwent free radical polymerization at room temperature to obtain a PNIPAm / Tre hydrogel with a thickness of 3 mm. The remaining precursor solution was poured out, and then deionized water was added to the upper chamber to fully soak the PNIPAm / Tre hydrogel, resulting in a swollen PNIPAm / Tre hydrogel with a thickness of 8 mm. The deionized water was then poured out, and then a 1.0 wt% pyrrole solution was added to the upper chamber to fully soak the swollen PNIPAm / Tre hydrogel for 24 hours. The remaining pyrrole solution was poured out, and then ammonium persulfate (APS) solution (0.1 mol L⁻¹) was added. -1 Soak the hydrogel thoroughly for 1 hour to allow in-situ polymerization of polypyrrole on the hydrogel surface. Pour off the remaining ammonium sulfate (APS) solution, and the selected PM layer can then be used. SL A black photothermal layer PM is introduced on the back. EDL (i.e., PNIPAm / Tre / PPy hydrogel), and obtained PM, a photothermal material for efficient separation of lithium and magnesium.

[0037] Comparative Example 1 Based on Example 1, trehalose is omitted, while other operating steps and conditions are the same as in Example 1. This can be done by selecting the PM layer. SL PNIPAm / PPy hydrogel was introduced on the back side to obtain the corresponding photothermal material.

[0038] Performance testing The relevant properties of the photothermal material PM obtained in Example 1 and Comparative Example 1 were tested using the following methods: 1) Scanning Electron Microscopy (SEM): Using a field emission scanning electron microscope (SEM), a high-energy electron beam is used to scan the sample under test and excite secondary electrons. After obtaining the secondary electron information, microscopic imaging is performed to observe the microscopic morphology of the sample.

[0039] 2) Atomic Force Microscopy (AFM): Atomic force microscopy (AFM) determines the surface roughness of electrode samples. The surface roughness test range is 10 × 10 μm.

[0040] 3) Differential Scanning Calorimetry (DSC): The evaporation and melting behavior of the samples were analyzed using a differential scanning calorimeter (HSC-4). After removing surface water from the fully expanded hydrogel, a small amount of hydrogel was weighed and tightly sealed in an aluminum crucible. The hydrogel sample was then incubated at 5°C under a nitrogen atmosphere. o C min -1 The heating rate is at 25 o C Up to 140o Evaporation behavior tests were conducted within a temperature range of C, and the enthalpy of vaporization of the hydrogel was analyzed based on the curves; the hydrogel samples were then subjected to evaporation at 5°C under a nitrogen atmosphere. o C min -1 Cooling rate to -30 o C, and maintain that temperature for 10 minutes, then at 5 o C min -1 The heating rate is at -30 o C to 30 o The melting behavior of the samples was tested within the temperature range of C, and the melting behavior of the samples was analyzed based on the curves.

[0041] 4) Rheometer: The storage modulus (G') and loss modulus (G'') of the sample are measured using a rheometer at different oscillation frequencies. The test system is a parallel plate, with the strain (stress) fixed in oscillation mode, and the frequency variation range is 0.6-600 rad / s. -1 .

[0042] 5) Photothermal interface water evaporation test The photothermal interface evaporation experiment was conducted at an ambient temperature of approximately 22°C. o C. The test was conducted under conditions of approximately 20% relative humidity. A self-made photothermal interface evaporation device was used, which mainly consists of a photothermal layer, a thermal insulation layer (polystyrene foam), and a water transport layer (hydrophilic cotton swabs). A 20 mm × 20 mm sample was placed within the thermal insulation material and then placed above a glass container containing 40 mL of water. Water was continuously transported to the surface of the photothermal material via capillary action through the hydrophilic cotton swabs. The light source was a solar simulator equipped with an AM 1.5G standard optical filter. After the sample surface temperature stabilized for 30 minutes, the change in water mass was monitored in real time using an electronic balance with an accuracy of 0.0001 g to calculate the water evaporation rate and photothermal conversion efficiency.

[0043] Water evaporation rate ( v )for: Where, d m This refers to the change in the mass of the apparatus during the evaporation process. S d represents the irradiation area of ​​the photothermal material. t This refers to the test time.

[0044] 6) Photothermal Enhanced Lithium Extraction Performance Test The SELE apparatus is used for the extraction of Li from different brines. + Extraction. The lower chamber of the SELE device circulates brine, while the open design of the upper chamber allows PM to directly absorb sunlight and convert it into heat energy, triggering evaporation of the water and driving the transmembrane transport of salt ions with the water. At 1 kW m³ / s... -2Li can be achieved by evaporating stably for 1 hour under light intensity. + Selection and enrichment to increase light intensity to 2 kW m -2 Furthermore, by cutting off the circulating brine, the PM temperature exceeded the LCST due to the high light intensity and the loss of circulating water as a cooling source, and the lithium-rich brine was desorbed within 5 minutes. The desorbed lithium-rich brine was collected and tested using atomic absorption spectrometry to obtain detailed salt concentrations in the lithium-rich brine.

[0045] SEIE's lithium-magnesium separation factor ( )for:

[0046] in and Representing Li + and Mg 2+ The concentration.

[0047] Test Example 1: Morphology and Structural Characteristics of PM like Figure 4 As shown in Figure a, the photothermal material PM obtained in Example 1 is composed of PM SL and PM EDL Composed of a two-layer structure, PM SL A hydrophobic, yellowish-brown film, PM EDL As a black gel film, PM maintains excellent adhesion of its bilayer structure even when inverted, effectively avoiding the problem of high mass transfer resistance caused by the physical bonding of the lithium selective layer and the photothermal layer. Compared to PNIPAm / PPy hydrogels, PM incorporates trehalose with abundant hydroxyl structures. EDL It exhibits superior mechanical properties. This is mainly due to the abundant -OH groups in the trehalose polymer chain, which can enhance the mechanical properties of the polymer network structure through strong hydrogen bonding.

[0048] like Figure 4 As shown in b, PM EDL The strain can reach 94.9%, and the corresponding stress is 161.54 kPa, both of which are better than the PNIPAm / PPy hydrogel without trehalose (strain: 85.2%, stress: 150.75 kPa).

[0049] like Figure 4 As shown in Figure c, the energy stored and dissipated by the hydrogel under oscillating stress is represented by the storage modulus (G') and loss modulus (G''), respectively. PNIPAm / PPy hydrogel and PM EDL In the frequency range of 0.1 ~ 100 rad / s -1 The internal G' is always greater than G'', which indicates the elastic behavior of the well-crosslinked polymer network in conventional hydrogels. EDLThe G' value of PM2.5 is higher than that of PNIPAm / PPy hydrogel, indicating that the strong hydrogen bonding of trehalose enables its polymer network to form a more robust and durable cross-linked structure, thereby enhancing the overall elastic properties. PM2.5, on the other hand, exhibits higher G' than PNIPAm / PPy hydrogel. EDL The G'' of PM2.5 is also higher than that of PNIPAm / PPy hydrogel. This is because although the strong hydrogen bonding has high bond energy, it is still a reversible bond. Under external force, it will break and recombine. This dynamic process itself requires the absorption and dissipation of a large amount of energy, providing the system with a strong viscous dissipation mechanism. Therefore, PM2.5... EDL The simultaneous increase of G' and G'' indicates that the polymer network structure has both a superior elastic structure and dissipates more energy (greater viscous resistance).

[0050] like Figure 5 As shown in diagram a-5f, PM exhibits a tightly integrated two-layer structure. Figure 5 a) By the top-level PM EDL and the bottom-level PM SL Composition, with a top layer of lithium photothermal PM exhibiting thermostrictive properties. EDL It exhibits a typical porous structure, with pore sizes of 10-15 μm at temperatures below the lower LCST. Figure 5 b). Due to PM EDL Due to its thermosensitive properties, when the temperature rises above LCST, the PNIPAm chains undergo a phase transition related to "dehydration-induced shrinkage," resulting in a significant shrinkage of the porous network and a reduction in pore size to 2-5 μm. Figure 5 c). PM SL The cross-sectional SEM image (bottom) shows that a dense, ultrathin polyamide layer was formed on the graphene substrate. Figure 5 d). Compared to the natural wrinkle morphology of the original rGO surface, PM SL After interfacial polymerization, a representative polyamide layer is formed, characterized by irregular ripples and valley-like surface features. Figure 5 e). This morphology originates from the difference in rapid interfacial polymerization and shrinkage between the QPEI-containing aqueous phase and the TMC-containing oil phase during the formation of the polyamide layer, resulting in a more pronounced ridge-valley structure. This corrugated surface effectively increases the interfacial area, which is beneficial for accelerating Li... + Through PM SL The transmission was further identified using AFM. SL Compared to the original rGO surface, the PM surface morphology after interface aggregation... SL The surface exhibits a more pronounced wrinkled structure. Figure 5 f).

[0051] Test Example 2: Photothermal Evaporation Performance Test like Figure 6As shown in figure a, the introduction of black PPy makes the PNIPAm / PPy hydrogel and PM... EDL All of them possess excellent broadband light absorption capabilities, achieving an absorption rate of approximately 99% across the entire solar spectrum.

[0052] like Figure 6 As shown in b-6c, at the air-water interface, absorbed solar energy is efficiently converted into thermal energy. This is achieved under different solar radiation intensities (0.25-2 kW m²). -2 Under ) PNIPAm / PPy and PM EDL The surface temperatures all showed a gradual upward trend. At 1.25 kWm -2 Under these conditions, the temperature rise showed a significant accelerating trend, with the PNIPAm / PPy hydrogel exhibiting a slightly faster heating rate than PM. EDL This stems from the fact that both hydrogels reached the LCST (approximately 32°C) of PNIPAm, at which point the surface state changed from hydrophilic to hydrophobic, triggering rapid interfacial heating. Simultaneously, PM, rich in trehalose... EDL The abundance of -OH groups in the network makes its dehydration process much slower than that of PNIPAm / PPy hydrogels. When the surface temperature exceeds LCST, water is expelled from the hydrogel, resulting in a thickness reduction of approximately 75% for PNIPAm / PPy, while PM... EDL The thickness reduction rate is 60%.

[0053] like Figure 6 As shown in d-6e, a PM with a diameter of 45mm and a thickness of 8mm is used. EDL Test at 2 kW m -2 Desorption under light intensity ( Figure 6 d) PM within the first 60 seconds EDL No significant desorption occurred because the surface temperature did not reach above LCST in the initial stage of illumination, and PM2.5 temperature increased after 60 seconds. EDL The surface temperature is greater than LCST and the aqueous solution desorbs outward. The aqueous solution is carefully collected using a syringe, and its volume is recorded. (PM) EDL Desorption occurs rapidly within 180 s, allowing for the collection of 2 mL of aqueous solution, at which point the PMEDL thickness decreases to 2 mm. Figure 6 e).

[0054] like Figure 7 As shown in a-7f, the water phase in the hydrogel is mainly divided into bound water (BW), intermediate water (IW), and free water (FW). EDL Because trehalose contains a relatively high number of hydroxyl groups ( Figure 7 a), compared to PNIPAm / PPy ( Figure 7 b), contains more BW and IW. PNIPAm / PPy and PMEDL The saturated water content was 32 g g. -1 and 36.4 gg -1 ( Figure 7 c). PM EDL The high water absorption rate is due to the introduction of trehalose, whose abundant hydroxyl groups can form a strong hydrogen bond network. Differential scanning calorimetry (DSC) melting curves show that PM... EDL Its enthalpy of fusion is lower than that of water and PNIPAm / PPy, indicating that it is transitioning from aqueous state to bound water and intermediate water. Figure 7 d). Accordingly, PM EDL The enthalpy of evaporation of the treated water was measured to be 1061.8 J g. -1 The concentration was significantly lower than that of pure water (2450.0 J g). -1 ) and PNIPAm / PPy (1586.7 J g -1 () Figure 7 e). Therefore, under different solar radiation intensities, PM EDL It exhibits a water evaporation rate (WER) higher than PNIPAm / PPy. This is when the solar radiation intensity is 1 kWm. -2 At that time, PMEDL reached 3.42 kg m -2 h -1 The WER was significantly better than that of PNIPAm / PPy (2.08 kg m -2 h -1 () Figure 7 These results demonstrate that the polymer film designed in this invention can withstand low solar radiation intensity (1 kW m). -2 This achieves a high water evaporation rate, promoting rapid lithium-ion transport and accumulation. Simultaneously, when solar radiation intensity increases to 1 kW m², [the process is similar to achieving this]. -2 This can accelerate lithium-ion desorption and collection.

[0055] Test Example 3: Photothermal Lithium Extraction Performance Test like Figure 8 As shown in a-8f, this invention explores PM containing different Mg 2+ / Li + The performance of SELE in brine with varying molar ratios alters the Mg content. 2+ / Li + The molar ratio ranges from 1:1 to 20:1, with a fixed Li + The concentration is 100 mmol / L -1 With Mg 2+ / Li + As the molar ratio gradually increases, the separation factor tends to increase. In Mg 2+ / Li +At a molar ratio of 1:1, the separation factor reaches as high as 36.46. However, in Mg... 2+ / Li + When the molar ratio is 20:1, the corresponding separation factor is as high as 80.25 ( Figure 8 a). Regardless of low or high Mg 2+ / Li + In comparison, PM demonstrated excellent Li + / Mg 2+ The separation performance is far superior to currently reported membrane-based SELE systems. It also verifies that Li... + Able to PM EDL Li continued to accumulate in Li, and after 200 min, Li + The concentration gradually increases until it matches the concentration in the original feed solution (Li). + = 100 mmol L -1 Mg 2+ / Li + (Molar ratio = 1). At 300 min, the concentration had already exceeded the original solution concentration, reaching 300 mmol / L. -1 ( Figure 8 b). As a control experiment, it only used PM2.5. SL The layer is used for photothermal lithium extraction. In Li + = 100 mmol L -1 Mg 2+ / Li + When the molar ratio is 1, its separation factor is only 2.44, and its separation performance is far worse than that of PM (which has continuous lithium-ion channels). Figure 8 c). Additionally, commercial nanofiltration membranes NF90 and NF270 are used instead of PM. SL A control experiment was conducted, and its Li + / Mg 2+ The separation factors are 5.0 and 5.5 ( Figure 8 d), This indicates that the SEIE system of the present invention possesses Li + / Mg 2+ It exhibits both high separation performance and a degree of scalability. The above results verify the selective passage of Li under continuous sunlight irradiation. + Able to continuously improve from PM SL To PM EDL This technology enables efficient transport and enrichment of lithium ions in low-grade brine, achieving superior SELE performance. Thanks to the integrated PM with continuous lithium-ion channels, Li-ion extraction can be achieved even with varying sunlight intensity. + Continuous selection, enrichment, and desorption effectively alleviate PM2.5 pollution. SL Interface concentration polarization enhances Li + / Mg2+ Separation performance.

[0056] This invention further validates the use of PM for extracting nutrients from low-grade brine (Li). + Concentration below 0.26 g / L -1 or Mg 2+ / Li + SELE application is performed when the mass ratio is greater than 6.15. Fixed Mg 2+ / Li + With a molar ratio of 10:1, the PM-based SELE system was tested at lower Li... + The ability to extract lithium resources from brine of varying concentrations, including Li + Concentration range from 100 mmol / L -1 Up to 20 mmol / L -1 With the original Li + As the concentration gradually decreases, the Li in the lithium-rich solution... + The concentration also decreased accordingly. It is worth noting that this did not affect the PM's ability to react with various Li+ molecules. + Concentration, high Mg 2+ / Li + Separation performance of brine solutions with varying molar ratios. Even in Li + Concentrations as low as 20 mmol / L -1 At that time, its separation factor was still as high as 69.50, verifying that PM has the ability to efficiently extract lithium from low-grade brine. Figure 8 Therefore, PM exhibits superior lithium selectivity and enrichment performance, exceeding that of SEIE (previously reported membrane separation technology). Figure 8 f).

[0057] The above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a photothermal material for efficient lithium-magnesium separation, comprising the following steps: Step 1: A polyamide layer is polymerized at the interface of the substrate film material with an aqueous solution of quaternized polyethyleneimine and a solution of trimesoyl chloride to obtain a layer with Mg 2+ / Li + Selective screening function selection layer PM SL ; Step 2: Temperature-sensitive monomers, trehalose, cross-linking agents, and initiators are applied to the selective layer PM. SL A thermosensitive hydrogel is formed on the back side via free radical polymerization. Then, a light absorber is added to the surface of the thermosensitive hydrogel via in-situ polymerization or physical mixing, thereby selectively absorbing PM... SL A photothermal layer PM is introduced on the back. EDL This yields a photothermal material for efficient lithium-magnesium separation.

2. The preparation method according to claim 1, characterized in that, In step 1, the preparation method of the quaternized polyethyleneimine is as follows: quaternized polyethyleneimine is obtained by modifying polyethyleneimine with a haloamine or a haloamine salt. The temperature of the above reaction is 50~100℃ and the reaction time is 5~15h; The mass ratio of haloamine or haloamine salt to polyethyleneimine is 1: (5~20); The structural formula of the haloamine is: X-(CH2) m -NH2, where X is F, Cl, Br, I, and m is 1, 2, 3, 4, 5, or 6; Preferably, the haloamine salt is 2-bromoethylamine hydrobromide or 2-bromoethylamine hydrochloride.

3. The preparation method according to claim 1, characterized in that, In step 1, the concentration of the quaternized polyethyleneimine aqueous solution is 0.5~5 wt%; the concentration of the pyromellitic pyromellitic chloride solution is 0.1~1 wt%; and the solvent of the pyromellitic pyromellitic chloride solution is selected from one or more of n-heptane, n-hexane, dichloromethane, chloroform, tetrahydrofuran, acetone, ethyl acetate, methanol, ethanol, DMSO and DMF.

4. The preparation method according to claim 1, characterized in that, In step 1, the substrate film material is a reduced graphene oxide film, a graphene oxide film, a carbon nanotube film, or a Ti3C2T film. X MXene membrane.

5. The preparation method according to claim 4, characterized in that, The substrate film material is a reduced graphene oxide film, and its preparation method includes the following steps: Using polytetrafluoroethylene, nylon-6, or nylon-66 as filter membranes, the graphene oxide dispersion is filtered to form a graphene oxide membrane, which is then partially reduced by ultraviolet light irradiation to obtain a reduced graphene oxide membrane. The duration of ultraviolet light irradiation is 0.5 to 5 hours. The concentration of the graphene oxide dispersion was 0.05–0.5 mg / mL. -1 .

6. The preparation method according to claim 1, characterized in that: The thermosensitive monomer is selected from one or more of N-isopropylacrylamide, N-vinylcaprolactam, polyethylene glycol methyl ether methacrylate, 2-(2-methoxyethoxy)ethyl methacrylate, N-vinylpyrrolidone, hydroxypropyl acrylate, N-hydroxyethylacrylamide, N-hydroxypropylacrylamide, and N-isobutylacrylamide. The crosslinking agent is selected from one or more of ethylene glycol dimethacrylate (EGDMA), polyethylene glycol diacrylate (PEGDA), N,N'-methylenebisacrylamide (MBAA), pentaerythritol tetraacrylate (PETTA), 1,3-butanediol dimethacrylate (BGDMA), 1,4-butanediol diacrylate (BDDA), 1,6-hexanediol diacrylate (HDDA), 1,6-hexanediol dimethacrylate (HDDMA), neopentyl glycol diacrylate (NPGDA), and trimethylolpropane triacrylate (TMPTA). The initiator is a mixture of ammonium persulfate and sodium bisulfite, a mixture of ammonium persulfate and sodium bisulfite, a mixture of sodium persulfate and sodium bisulfite, a mixture of potassium persulfate and sodium bisulfite, a mixture of sodium persulfate and sodium bisulfite, a mixture of potassium persulfate and sodium bisulfite, a mixture of potassium persulfate and tetramethylethylenediamine, a mixture of ammonium persulfate and tetramethylethylenediamine, or a mixture of sodium persulfate and tetramethylethylenediamine. The mass ratio of the thermosensitive monomer to trehalose is (2~10):

1.

7. The preparation method according to claim 1, characterized in that, The light absorber is selected from one or more of carbon black, activated carbon, graphene oxide, carbon nanotubes, Mxene, and polypyrrole; Preferably, the light absorber is polypyrrole; the polypyrrole is added to the surface of the thermosensitive hydrogel by in-situ polymerization; preferably, the polymerizing monomer is pyrrole with a concentration of 0.05~2 wt%; preferably, the initiator used for polymerization is selected from ammonium persulfate, potassium persulfate and sodium persulfate with a concentration of 0.05~2 wt%.

8. The preparation method according to claim 1, characterized in that, In step 2, a diffusion cell is used as the reaction carrier for polymerization. The diffusion cell consists of two independent chambers, upper and lower, connected by a selective layer PM. SL Separation.

9. A photothermal material for efficient lithium-magnesium separation, characterized in that, The photothermal material is prepared by any one of the methods described in claims 1-8.

10. The application of the photothermal material of claim 9 in lithium extraction from salt lakes or seawater.

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