A photothermally driven ionic separation device, method of manufacture and use

Abstract

This invention relates to a photothermal-driven ion separation device, its preparation method, and its application. The device includes a porous substrate with a photothermal layer disposed on a first surface of the substrate. The photothermal layer absorbs light and generates heat. An ion separation membrane is disposed on a second surface of the porous substrate, selectively allowing ions from a solution to permeate. The pore structure within the porous substrate connects the first and second surfaces. In use, the ion separation membrane is in contact with the solution. Capillary force generated by a water transport channel drives water and permeable ions in the solution through the ion separation membrane to the pore structure of the porous substrate. Water evaporates in the photothermal layer, and ions are deposited within the pore structure of the porous substrate. It can be used to separate ions with different charges in a solution, such as lithium ions and magnesium ions.

Description

Technical Field

[0001] This invention relates to membrane technology, and more particularly to a photothermal driven ion separation device, its preparation method, and its applications. Background Technology

[0002] Lithium (Li) is a strategic non-renewable resource used in high-tech products such as batteries, ceramics, glass, and alloys. With the surge in consumer electronics and electric vehicles, lithium supply shortages are expected to worsen. Salt lake brines account for approximately 70% of the Earth's recoverable lithium, most of which consists of high concentrations of magnesium ions. Currently, about 59% of lithium is produced from salt lake brines with low magnesium / lithium (Mg / Li) ratios. In my country, 80% of usable lithium is stored in salt lakes, making lithium extraction from these lakes a crucial way to ensure lithium supply. However, compared to the low Mg / Li ratio salt lakes of countries like Peru in South America, the Mg / Li ratios in my country's salt lakes are as high as tens or even hundreds, making lithium extraction from them very difficult using traditional methods. Currently, only a very small number of salt lakes with low Mg / Li ratios are being mined. Therefore, as the world's largest lithium consumer, my country is also a major lithium importer, relying on imports for about 80% of its lithium, posing a significant risk.

[0003] To alleviate the shortage of available lithium resources, there is growing interest in extracting lithium from brines with high Mg / Li ratios. Currently, various methods exist for recovering lithium from brine with high Mg / Li ratios. For example, Li can be extracted from brines with Mg / Li ratios of 325, 40, and 37.5 using tributyl phosphate / FeCl3 extraction, sodium metasilicate nonahydrate precipitation, and lithium-ion sieving. While the Mg / Li ratio of the original brine can be effectively reduced, the problems of lithium resource loss and liquid waste generation remain unresolved. Electrochemical lithium recovery faces challenges related to concentrated Mg... 2+ / Li + The mixture exhibits good selectivity and recovery rate, but current electrochemical devices are costly and have relatively poor recovery stability. Furthermore, significant progress has been made in separating fine chemicals using membrane separation technology. Among these, nanofiltration (NF) membranes, through a combination of size sieving and charge repulsion effects, are emerging as a highly efficient and environmentally friendly alternative for lithium extraction. Given Mg... 2+ and Li + The hydration radii of the ions are very close, and the permeability of Li through polymer membranes is generally similar to that of Mg. 2+ / Li + Selectivity phase trade-offs. Meanwhile, improved membrane separation methods have also been developed for Mg... 2+ / Li + The separation and selectivity of ion mixtures are achieved through nanofluidic devices made of two-dimensional materials and crystalline porous frameworks, which are limited by miniaturization and high cost. From high Mg... 2+ / Li + Simpler preparation methods for extracting lithium from brine more efficiently still do not meet the urgent need.

[0004] Therefore, membrane separation technology is used in high Mg 2+ / Li + Nucleotide (NF) membranes show great potential in the separation of mixed salt solutions. However, high-concentration brine creates a high osmotic pressure gradient across the membrane, requiring applied pressures far exceeding the mechanical strength of the membrane module. Therefore, traditional NF membrane treatment processes typically involve diluting the high-concentration brine 10-20 times with a large amount of fresh water during the pretreatment stage. Furthermore, NF membrane separation processes only produce lithium-rich solutions, requiring further concentration to obtain solid lithium products. This necessitates energy-intensive processes such as thermal distillation or high-pressure reverse osmosis to achieve the desired lithium-rich solution concentration. Summary of the Invention

[0005] To address the high cost and difficulty of ion separation in salt solutions, this invention provides a photothermal-driven ion separation device. This device utilizes the synergistic effect of an ion separation membrane and a solar evaporator to directly extract lithium chloride (LiCl) powder from salt lake brine. This provides an effective method for obtaining high-purity lithium directly from salt lake brine using only sustainable energy sources. It is environmentally friendly, reduces the integration of energy-intensive processes, and lowers energy consumption and operating costs.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: a photothermal driven ion separation device, comprising a porous substrate with a pore structure, a photothermal layer disposed on a first surface of the porous substrate, and an ion separation membrane disposed on a second surface. The positional relationship between the first and second surfaces is not limited, but preferably the first and second surfaces are arranged opposite each other. In use, the first surface is the upper surface, and the second surface is the lower surface. The pore structure on the porous substrate connects the first and second surfaces, which facilitates the transport of water from the first surface to the second surface. The pore structure can be configured in the following two ways: Method 1, the porous matrix itself can be a water-absorbing material or at least the inner wall material of the pore structure can be a hydrophilic material, and the pore structure can be micropores or nanopores. Water can be transported within the pore structure through capillary force; Method 2, the pore structure of the porous matrix is ​​filled with a hydrophilic material, and micropores or nanopores are provided on the hydrophilic material. The capillary force generated by the water transport channel serves as the driving force for water transport. Under the action of capillary force, water passes through the ion separation membrane to the photothermal layer and evaporates. The ions that have passed through the ion separation membrane are deposited in the water transport channel.

[0007] As a preferred method, the porous matrix is ​​a sand core with a pore size of G1-G6, preferably G6. The pore structure of the sand core is filled with a hydrophilic material, and the hydrophilic material is provided with nanoscale water transport channels. The water transport channels can generate pressure at the level of hundreds of megapascals as the driving force for water transport.

[0008] As a preferred approach, at least one of the ion separation membrane, photothermal layer, and hydrophilic material is synthesized in situ on the sand core to form an integral structure, which is beneficial to improving the performance stability of the device. Even more preferred is that all three are synthesized in situ on the sand core, which improves layer adhesion and device stability.

[0009] As a preferred approach, the photothermal layer is a polymer layer capable of absorbing light and generating heat. This layer has a porous structure to facilitate the evaporation of water molecules. Specifically, it can be polypyrrole, light-absorbing gel, or a polymer that can be blended with a black material to form a porous film. The porous film can be formed through phase inversion or electrospinning processes, or it can be formed in situ on the first surface of a sand core. The black material can be an organic polymer, such as polyaniline (PANI), or an inorganic material, such as carbon nanotubes (CNTs), carbon black, carbon powder, graphene, MXene, etc. The photothermal layer can also be a gel in which photothermal nanomaterials are dispersed, such as a hydrogel or aerogel.

[0010] Another aspect of the present invention provides a method for preparing a photothermal driven ion separation device. First, a porous substrate is selected, and a pore structure is provided on the porous substrate that penetrates a first surface and a second surface. A photothermal layer is provided on the first surface, and an ion separation membrane is provided on the second surface. Preferably, a hydrophilic material with water transport channels is provided in the pore structure.

[0011] In a further preferred embodiment, the photothermal layer is polypyrrole formed by alternating in-situ polymerization on the first surface of the sand core. This polymer has strong light absorption capacity, which is beneficial for improving the evaporation efficiency of the device. Furthermore, it has good compatibility with the sand core, forming a stable bonding strength. The specific preparation method is as follows: S01 Prepare an aqueous solution of pyrrole and an aqueous solution of ammonium persulfate, preferably with a mass ratio of pyrrole to ammonium persulfate of 1:(2-4); S02 Coat the pyrrole aqueous solution onto the first surface of the porous substrate; S03 Coat the ammonium persulfate aqueous solution onto the first surface of the porous substrate obtained in S02, and allow it to react statically; S04 Repeat steps S02 and S03 until the desired photothermal layer is formed. In this invention, under the action of the oxidant (ammonium persulfate), a neutral pyrrole monomer molecule loses an electron and is oxidized into a cationic free radical. Then, the two cationic free radicals combine to generate a dication of dipyrrole. This dication undergoes disproportionation to generate a neutral dipyrrole. Then, the dimerpyrrole is oxidized, combines with cationic free radicals, and then disproportionates to form a trimer. This reaction continues until chain-like PPy molecules with a degree of polymerization n are formed, ultimately creating the photothermal layer. The reaction formula is:

[0012]

[0013] As a more specific implementation method, the photothermal layer is prepared as follows: (1) Prepare a pyrrole aqueous solution: the preferred content range of pyrrole in the pyrrole aqueous solution is 0.5-5wt%, and more preferably, 1.035mL of pyrrole solution is added dropwise to 50mL of aqueous solution, and the pyrrole aqueous solution is obtained after magnetic stirring for 10min; (2) Prepare an ammonium persulfate aqueous solution: the preferred content range of ammonium persulfate in the ammonium persulfate aqueous solution is 1-15wt%. If the content is lower than this, the self-polymerization time of pyrrole monomer will be prolonged, and the reaction product polypyrrole will not cover the surface of the sand core completely; if the content is higher than this, the reaction product polypyrrole will fill the pores inside the sand core, reduce the porosity of the sand core, reduce the pore size of the sand core and reduce the hydrophilicity of the sand core. The optimal solution preparation method is as follows: Add 3.36g of white ammonium persulfate powder to 50mL of aqueous solution, stir magnetically for 10min and set aside; (3) Coating with pyrrole solution: Use a dropper to take a certain amount (determined according to the area of ​​the selected sand core) of pyrrole aqueous solution and add it to the surface of the sand core, and then use a brush to spread it evenly to ensure that the entire surface of the sand core is wetted; (4) Coating with ammonium persulfate solution: Use a dropper to take a certain amount (determined according to the area of ​​the selected sand core) of ammonium persulfate aqueous solution and add it to the surface of the sand core, and use a brush to spread it evenly, and let it stand for 1-20min; (5) After wiping the residual aqueous solution on the surface of the sand core with lint-free paper, add a certain amount of pyrrole aqueous solution again to completely wet the film surface, let it stand for a certain time, the reaction time is selected according to the reaction process, preferably 1-20min; (6) Continue to repeat the above steps (4) and (5) for a total of three cycles, and terminate the reaction by adding ammonium persulfate solution. Thus, a photothermal layer for solar photothermal conversion was prepared by in-situ polymerization reaction on the surface of the sand core.

[0014] As a preferred method, the hydrophilic material is synthesized in situ within the porous structure. This setup allows for the control of the pore size and wettability of the water transport channels by adjusting the polymer composition, content, or synthesis conditions. The hydrophilic material can be formed by the polymerization of two or more monomers, and can be selected from one or more of the following materials: polyethersulfone, polyvinylidene fluoride (PVDF), polyimide (PI), polyester (PP), polytetrafluoroethylene (PTFE), cellulose acetate (CA), polysulfone (PSF or PSU), polyacrylonitrile (PAN), hydrogel, etc., with polyethersulfone being preferred. The preparation method is as follows: S01, dissolve polyethersulfone particles, polyethyleneimine, and polyethylene glycol in N,N-dimethylformamide to form a polymer solution; S02, pour the prepared polymer solution into the porous structure of the porous matrix, ensuring that the porous structure is completely wetted by the polymer solution, and seal it for a set time; S03, remove the porous matrix and place it in deionized water for a non-solvent-induced phase inversion to form a hydrophilic polymer within the porous structure.

[0015] The preferred preparation method for hydrophilic materials is as follows: (1) Polyethersulfone (PES) particles, polyethyleneimine (PEI) and polyethylene glycol (PEG) are added to N,N-dimethylformamide (DMF) solvent to prepare a polymer solution of a certain viscosity. The polymer solution contains 3-15 wt% polyethersulfone (PES) particles, 0.5-10 wt% polyethyleneimine, and 0.5-3 wt% polyethylene glycol. The polymer solution is magnetically stirred at 25-50°C for 6-12 h, and then allowed to stand at room temperature for 8-12 h to remove bubbles before use. (2) Slowly add the prepared polymer solution to the microporous sand core to completely wet it, and seal it for 24 hours; (3) Take out the microporous sand core containing the polymer solution that is completely wetted, quickly place it in deionized water for water bath non-solvent-induced phase transformation, and let it stand for 24 hours to complete the phase transformation of the polymer. After the phase transformation is completed, the pore structure of the sand core is filled with polymer; (4) Take out the sand core and transfer it to new deionized water to allow the internal polymer to fully transform. After the phase transformation is completed, the porous matrix is ​​stored in deionized water for later use. After the polymer solution with N,N-dimethylformamide (DMF) as the continuous phase is made into a uniform liquid film, it is immediately immersed in water. Dimethylformamide and polyethylene glycol (PEG) dissolve in water, so that the polyethersulfone (PES) polymer solution with the solvent as the continuous phase is transformed into a three-dimensional macromolecular network gel with polyethersulfone as the continuous phase, thereby forming a polyethersulfone separation membrane.

[0016] Further preferably, the polymer solution in step (1) is obtained by dissolving 7.5 wt% polyethersulfone (PES) particles, 3.5 wt% polyethyleneimine (PEI), and 2 wt% polyethylene glycol (PEG) in DMF solvent. The polymer solution is magnetically stirred at 40°C for 12 h and then allowed to stand for degassing for 10 h. The type (single-chain or branched) and molecular weight of the polyethyleneimine are not limited, but preferably the molecular weight of the polyethyleneimine is 70,000 and the molecular weight of the polyethylene glycol is 400. This molecular weight provides more positively charged amino groups in the subsequently formed polymer membrane, which can improve the adhesion of the in-situ polymerized nanofiltration layer, as well as improve the hydrophilicity and water flux of the polymer membrane. The type and molecular weight of the non-solvent additives are not limited, nor are the types of solvents used.

[0017] In this invention, the ion separation membrane is a nanofiltration membrane. It can be a commercially available finished membrane laminated onto a sand core, or the membrane layer can be self-made, preferably self-made. This allows for optimization of the nanofiltration membrane's charge properties and pore structure to selectively allow the desired ions to pass through, thereby improving ion separation efficiency. The preparation method of the ion separation membrane in this invention is as follows: S01, prepare an aqueous solution of piperazine and sodium dodecylbenzenesulfonate as the first solution; prepare a hexane solution of trimesoyl chloride as the second solution; S02, immerse the second surface of the porous substrate in the first solution, and after a set immersion time, remove it and immerse it in the second solution for polymerization reaction, generating a polymer on the second surface to obtain the nanofiltration layer. As a preferred embodiment, the mass fraction of piperazine in the first solution is 0.1-5 wt%, the mass fraction of sodium dodecylbenzenesulfonate is 0.1-3.6 mmol / L, and the mass fraction of trimesoyl chloride in the second solution is 0.05-0.3 wt%. Further preferred preparation method of nanofiltration membrane is as follows: (1) Prepare an aqueous solution containing 0.1-5 wt% piperazine (PIP) and 0.1-3.6 mmol / L sodium dodecylbenzenesulfonate (SDBS), and stir magnetically at 20-40℃ for 1-5 h to obtain a completely dissolved PIP aqueous solution; (2) Prepare a n-hexane solution containing 0.05-0.3 wt% trimesoyl chloride (TMC), and stir magnetically at 20-40℃ for 1-5 h to obtain a completely dissolved TMC n-hexane solution; (3) Immerse the second surface of the core in the PIP aqueous solution for 0.5-10 min; (4) Remove the core from the PIP aqueous solution, remove excess water from the surface, and then immerse it in the n-hexane solution containing TMC for 10-360 s for interfacial polymerization reaction. The specific reaction formula is as follows:

[0018] The PIP monomer in the aqueous phase and the TMC monomer in the hexane solution undergo an irreversible rapid polycondensation reaction on the surface of the polymer-filled sand core, eventually forming a dense nanofiltration layer in situ on the surface of the sand core; (5) the sand core is removed from the hexane solution of TMC and slowly rinsed with pure hexane for 1-5 min to remove unreacted chemicals; (6) the microporous sand core with polymer polymerized in situ is placed in an oven at 50-80℃ and left to stand for 1-3 h, preferably at 50℃ for 2 h, to obtain a nanofiltration layer formed integrally with the sand core; (7) the sand core is removed from the oven and soaked in room temperature deionized water for later use. In order to improve the retention rate of the nanofiltration layer and improve the extraction efficiency of lithium ions, in step (1), the mass fraction of PIP in the aqueous solution of PIP & SDBS is 2wt%, the concentration of SDBS is 1.2mmol / L, and the concentration of TMC in the hexane solution is 0.15wt%. All are stirred for 2 h to obtain monomer solutions in the aqueous and oil phases. The immersion times of the sand core in the aqueous solution and the oil solution were 1 min and 30 s, respectively.

[0019] Furthermore, this invention provides applications for the aforementioned ion separation device. During use, the device floats in the solution to be extracted, with its first surface facing upwards to fully absorb sunlight and generate heat. The second surface is in contact with the solution and can be used to extract lithium ions or other ions. When the device is operating, water carries permeable ions through the ion separation membrane into the porous structure of the porous substrate. Water molecules, when heated, convert into water vapor and escape from the upper photothermal layer. Ions are deposited within the porous structure. After the device finishes operating, it is immersed in deionized water or rinsed with deionized water. The deposited ions dissolve in the deionized water, completing the ion extraction process.

[0020] The beneficial effects of this invention include: 1. The photothermal driven ion separation device of this invention uses sunlight and capillary force generated by capillary channels as the power source for water and ion transport, without the need for external energy, thus saving energy and being environmentally friendly;

[0021] 2. This invention enables the independent synthesis of hydrophilic materials on a photothermal driven ion separation device, allowing for free control of the hydrophilic properties and pore size of the materials, thereby controlling capillary forces and making them suitable for various application scenarios.

[0022] 3. This invention achieves stable heat transfer on the device and improves the evaporation efficiency of water vapor by integrally forming a photothermal layer on a porous aggregate;

[0023] 4. This invention improves the stability of ion filtration performance by integrally forming a nanofiltration membrane on a porous substrate, and the charge and pore size of the nanofiltration membrane can be adjusted according to the performance of the separated ions, thereby improving the separation efficiency.

[0024] 5. Interfacial solar evaporation is a sustainable and cost-effective clean water production technology that uses the heat generated by concentrated solar energy to promote water evaporation. The device in this invention is an effective method for obtaining high-purity lithium directly from salt lake brine using sustainable energy. It is environmentally friendly, reduces the integration of energy-intensive processes, and lowers energy consumption and operating costs.

[0025] 6. The device in this invention can directly concentrate high-concentration, high magnesium-to-lithium ratio brine from salt lakes. The extraction efficiency can be adjusted by changing the pore size and surface charge properties of the bottom nanofiltration membrane. The device in this invention is particularly effective for concentrating Li in salt lakes. + / Mg 2+ The separation factor can reach over 30, and the lithium chloride crystallization rate can reach 400 mg / m³. 2 The efficiency is above 1000 liters per hour. Compared to existing salt lake ion resource extraction technologies, this device can achieve the cyclical collection of lithium salt crystals by treating high-concentration salt lake water, ensuring that the resource extraction process is green, environmentally friendly, economical, and efficient. Attached Figure Description

[0026] Figure 1 The structural diagram of the device after being encapsulated with a hollow clamp in this invention;

[0027] Figure 2 The evaporation rate of pure water in different salt solutions under three sun irradiations;

[0028] Figure 3 Separation factor of the device in different salt solutions;

[0029] Figure 4 The lithium chloride crystallization rate of the device in different salt solutions.

[0030] In the diagram, 1 is the component, and 2 is the hollow clamping plate. Detailed Implementation

[0031] The present invention will be further explained in detail below with reference to the accompanying drawings and specific embodiments, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0032] The photothermal driven ion separation device of the present invention includes a porous substrate, which includes a first surface and a second surface arranged opposite to each other. The porous substrate has a uniformly distributed pore structure as a channel that runs through the first surface and the second surface. A photothermal layer, which is a porous membrane layer, is disposed on the first surface. A nanofiltration membrane layer is disposed on the second surface. The nanofiltration membrane layer can selectively transmit a certain type of ion, thereby achieving the separation of the ion from other ions. A hydrophilic material is filled in the pore structure. A water transport channel is disposed on the hydrophilic material. The water transport channel is a nanoscale channel, preferably a 10-220 nm nanochannel, which can generate a pressure of more than 18 MPa. In use, the first surface faces upward as the upper surface, and the second surface faces downward as the lower surface. The device floats in the solution to be extracted, with the lower surface in contact with the solution and the upper surface not in contact with the solution. Water and ions to be extracted in the solution permeate through the nanofiltration membrane to the hydrophilic material and are transported along the hydrophilic material. Under the action of the photothermal layer, the water absorbs heat and is converted into water vapor, which escapes through the photothermal layer. The ions to be extracted are deposited in the hydrophilic material, eventually forming solid crystals. The extraction method of the solid crystals is not limited. The solid crystals can be dissolved by immersing the device, or by rinsing the device with deionized water, or by directly separating the solid crystals from the device in other ways.

[0033] To ensure the device can float stably on the solution, the porous substrate can be a buoyancy material, allowing the device to float through its own buoyancy. Alternatively, buoyancy components can be installed on the device to make it float on the water surface. In this embodiment, hollow clamps 2 with buoyancy are installed on both sides of the device 1, such as... Figure 1 A gasket is provided between the hollow clamping plate 2 and the device 1. The hollow clamping plate 2 clamps the device 1. The hollow clamping plate 1 is a ring-shaped body that clamps the device 1 around its perimeter.

[0034] In this embodiment, the porous substrate is a sand core containing micropores. The sand core thickness is 3mm, the sand core pore diameter is G6, and the pore diameter range is 1.2~10μm.

[0035] The aforementioned devices can be used to separate ions with different charges or different pore sizes, such as allowing Li to... + Monovalent ions can pass through while blocking other polyvalent ions, such as SO42-. 2- Ca 2+ and Mg 2+ One application of this device is the separation of lithium and magnesium ions to extract lithium ions. The device selectively retains magnesium ions while allowing lithium ions to pass through, ultimately causing the lithium salt to crystallize and precipitate on top of the photothermal layer.

[0036] The fabrication method of the device will be further described below with reference to specific embodiments.

[0037] Example 1

[0038] The device fabrication method includes the following steps:

[0039] Step 1 involves in-situ synthesis of a photothermal layer on the first surface of the sand core. The synthesis method is as follows:

[0040] (1) Add 1.035 mL of pyrrole solution (analytical grade) dropwise to 50 mL of aqueous solution, stir magnetically for 10 min, and obtain a pyrrole aqueous solution with a mass fraction of 0.2 wt%.

[0041] (2) Add 3.36 g of ammonium persulfate white powder to 50 mL of aqueous solution and stir magnetically for 10 min to obtain ammonium persulfate solution;

[0042] (3) Using a dropper, a certain amount of pyrrole aqueous solution (determined according to the area of ​​the selected sand core) is added to the surface of the sand core. The amount of pyrrole aqueous solution on a unit area of ​​sand core is 0.4 mL / m². 2 Then use a brush to apply the coating evenly, ensuring that the entire surface of the sand core is wetted;

[0043] (4) Using a dropper, a certain amount of ammonium persulfate aqueous solution (determined according to the area of ​​the selected sand core) is added to the surface of the sand core. The amount of ammonium persulfate aqueous solution added per unit area of ​​sand core is 0.4 mL / m. 2 Apply the mixture evenly with a brush and let it stand for 3 minutes. During this process, pyrrole undergoes a polymerization reaction to form polypyrrole, as shown in the following reaction formula:

[0044]

[0045] (5) After wiping the surface of the sand core with lint-free paper to remove any remaining aqueous solution, apply 0.4 mL / m solution again. 2Add pyrrole aqueous solution dropwise to the sand core to completely wet the membrane surface, and let it stand for 3 minutes to react;

[0046] (6) Repeat steps (4) and (5) above for a total of three cycles, terminating the reaction by adding ammonium persulfate solution dropwise. Thus, a photothermal layer for solar photothermal conversion was prepared through in-situ polymerization on the surface of the sand core.

[0047] Step two involves filling the pore structure of the sand core with a hydrophilic material. The preparation method is as follows:

[0048] (1) Polyethersulfone particles, polyethyleneimine and polyethylene glycol were added to N,N-dimethylformamide (DMF) solvent to prepare a polymer solution with a certain viscosity. The concentration of polyethersulfone particles in the polymer solution was 7.5 wt%, the molecular weight of polyethyleneimine was 70,000 and the concentration was 3.5 wt%, and the molecular weight of polyethylene glycol was 400 and the concentration was 2 wt%. The polymer solution was magnetically stirred at 40°C for 12 h, and then allowed to stand at room temperature for 10 h to remove bubbles before use.

[0049] (2) The prepared polymer solution is slowly dripped into the microporous sand core pore structure from the second surface to completely wet it, and then sealed for 24 hours;

[0050] (3) Take out the microporous sand core containing polymer solution that is completely soaked, quickly place it in deionized water for water bath non-solvent-induced phase transformation, and let it stand for 24 hours to complete the phase transformation of the polymer.

[0051] (4) Remove the polymer-filled microporous sand core and transfer it to fresh deionized water for storage until use. Step 3 involves in-situ synthesis of a nanofiltration membrane on the second surface of the sand core. The preparation method is as follows:

[0052] (1) Prepare an aqueous solution containing 2 wt% piperazine (PIP) and 0.15 mmol / L sodium dodecylbenzenesulfonate (SDBS), and stir magnetically at 35°C for 2 h to obtain a completely dissolved PIP aqueous solution;

[0053] (2) Prepare a solution of n-hexane containing 0.15 wt% trimesoyl chloride (TMC), and stir magnetically at 35 °C for 2 h to obtain a completely dissolved TMC n-hexane solution;

[0054] (3) Immerse the second surface of the sand core in PIP aqueous solution for 1 minute, then remove it and remove excess water from the surface;

[0055] (4) The second surface is immersed in a hexane solution containing TMC for 30 seconds to carry out interfacial polymerization. The polymerization reaction formula is:

[0056]

[0057] In the formula, ※ represents piperazine or trimesoyl chloride monomer. During the reaction, the PIP monomer in the aqueous phase and the TMC monomer in the n-hexane solution undergo an irreversible rapid condensation reaction on the second surface of the sand core, ultimately forming a dense nanofiltration layer in situ on the sand core surface.

[0058] (5) Remove the surface-polymerized sand core from the hexane solution containing TMC and rinse it slowly with pure hexane for 1 minute to remove unreacted chemicals.

[0059] (6) Place the sand core in a 50℃ oven and let it stand for 2 hours to dry;

[0060] (7) Remove the sand core from the oven and soak it in room temperature deionized water. Remove it when using it.

[0061] The resulting device was encapsulated using a hollow clamp and gaskets, both of which were annular, securing the device around its upper and lower surfaces. The hollow clamp provided buoyancy, allowing the device to float on water. The device was placed in a mixed salt solution of magnesium chloride and lithium chloride with a total concentration of 80 g / L, where the mass ratio of lithium ions to magnesium ions was 1:1. The lithium extraction efficiency of the device was tested under three different sunlight intensities for 48 hours.

[0062] Example 2

[0063] The difference from Example 1 is that the salt solution to be extracted is different. In this example, the device is placed in a mixed solution of lithium chloride and magnesium chloride, with a lithium-magnesium ion mass ratio of 1:1 and a total concentration of 20 g / L for lithium chloride and magnesium chloride.

[0064] Example 3

[0065] The difference from Example 1 is that the salt solution to be extracted is different. In this example, the device is placed in a mixed solution of lithium chloride and magnesium chloride, with a lithium-magnesium ion mass ratio of 1:1 and a total concentration of 30 g / L for lithium chloride and magnesium chloride.

[0066] Example 4

[0067] The difference from Example 1 is that the salt solution to be extracted is different. In this example, the device is placed in a mixed solution of lithium chloride and magnesium chloride, with a lithium-magnesium ion mass ratio of 1:1 and a total concentration of 40 g / L for lithium chloride and magnesium chloride.

[0068] The water evaporation rate, separation factor, and lithium chloride crystallization rate of the devices in Test Examples 1-4 were measured. The separation factor was calculated as follows: Separation factor = Mass ratio of lithium to magnesium ions after separation / Mass ratio of lithium to magnesium ions before separation. Taking a mass ratio of lithium ions to magnesium ions in the salt solution to be extracted as 1:1 as an example, and assuming that the mass ratio of lithium ions to magnesium ions entering the sand core pore structure is 20:1, then the separation ratio is (20:1) / (1:1) = 20.

[0069] The lithium chloride crystallization rate is calculated as follows: lithium is the mass of lithium chloride powder collected per unit area of ​​the device per unit time via solar energy. In this invention, the lithium chloride powder collected by the device is dissolved in a certain volume of aqueous solution. The mass concentration of lithium ions in the aqueous solution is measured using an inductively coupled plasma spectrometer (ICP-SPS) to deduce the mass of the lithium chloride powder. For example, if the lithium ion concentration is 1 mg / L and the aqueous solution volume is 0.1 L, the mass of lithium is 0.1 mg. The mass of lithium chloride is then obtained, divided by the working area of ​​the separation membrane and the working time to finally obtain the lithium chloride crystallization rate.

[0070] Test results are as follows Figure 2-4 As shown, by Figure 2 It can be seen that as the concentration of the mixed salt solution of magnesium chloride and lithium chloride increases, the water evaporation rate and the separation factor remain essentially unchanged. Figure 4 It can be seen that the crystallization rate of lithium chloride increases with the increase of the mixed salt solution of magnesium chloride and lithium chloride, indicating that the device can adapt to salt solutions of various concentrations, and the separation efficiency is stable at over 30%. Moreover, in high-concentration salt solutions, it is beneficial to increase the crystallization rate of salt.

[0071] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A photothermally driven ionic separation device, characterized by: The porous substrate includes a first surface and a second surface, and the first surface and the second surface are connected by a pore structure. A photothermal layer is arranged on the first surface of the porous substrate, and the photothermal layer generates heat by absorbing light. An ion separation membrane is arranged on the second surface of the porous substrate, and the ion separation membrane selectively transmits ions in a solution. The pore structure of the porous substrate is connected to the first surface and the second surface, and the first surface is an upper surface and the second surface is a lower surface in use. The pore structure of the porous substrate is filled with a hydrophilic material, and the hydrophilic material is provided with micro-porous or nano-scale water transport channels. Capillary force generated by the water transport channels drives water and permeable ions in the solution to pass through the ion separation membrane to the pore structure of the porous substrate. The hydrophilic material is a hydrophilic polymer, and a polymer solution formed by dissolving polyether sulfone particles, polyethyleneimine with a molecular weight of 70,000, and polyethylene glycol with a molecular weight of 400 in N,N-dimethylformamide is used as raw material to be synthesized in situ in the pore structure of the porous substrate.

2. The photothermally driven ionic separation device of claim 1, wherein: The photothermal layer is formed by in-situ polymerization on the first surface of the porous substrate, and the ion separation membrane is formed by in-situ polymerization on the second surface of the porous substrate.

3. A method of fabricating a photothermally driven ionic separation device, the method comprising: The photothermal layer is polypyrrole, and the ion separation membrane is a nanofiltration membrane. The method comprises the following steps: A porous substrate is prepared, and the porous substrate includes a first surface and a second surface, and the first surface and the second surface are connected by a pore structure. A hydrophilic material is generated in situ in the pore structure, and the hydrophilic material is provided with nano-scale water transport channels. A photothermal layer is formed by in-situ polymerization on the first surface of the porous substrate. An ion separation membrane is formed by in-situ polymerization on the second surface of the porous substrate. The method for generating the hydrophilic material in situ in the pore structure of the porous substrate comprises the following steps: S1-1: Dissolve polyether sulfone particles, polyethyleneimine with a molecular weight of 70,000, and polyethylene glycol with a molecular weight of 400 in N,N-dimethylformamide to form a polymer solution. S1-2: Pour the prepared polymer solution into the pore structure of the porous substrate, so that the pore structure is completely infiltrated with the polymer solution, and then seal for a set time. S1-3: Take out the porous substrate and perform non-solvent induced phase inversion in deionized water to form a hydrophilic polymer in the pore structure. The method for generating the photothermal layer by in-situ polymerization on the first surface of the porous substrate comprises the following steps: S2-1: Prepare an aqueous pyrrole solution and an aqueous ammonium persulfate solution, and the mass fraction of ammonium persulfate in the aqueous ammonium persulfate solution is 1-15 wt%. S2-2: Apply the aqueous pyrrole solution to the first surface of the porous substrate. S2-3: Apply the aqueous ammonium persulfate solution to the first surface of the porous substrate obtained in S2-2, and then stand for reaction. S2-4: Repeat steps S2-2 and S2-3 until the desired photothermal layer is formed.

4. The method of claim 3, wherein: In S1-1, the mass fraction of polyether sulfone in the polymer solution is 3-15 wt%, the mass fraction of polyethyleneimine is 0.5-10 wt%, and the mass fraction of polyethylene glycol is 0.5-3 wt%.

5. The method of claim 3 or 4, wherein: In step S2-1, the mass fraction of pyrrole in the aqueous solution is 0.5-5 wt%.

6. The method of claim 3 or 4, wherein: The method for generating the ion separation membrane by in-situ polymerization on the second surface of the porous substrate comprises the following steps: S3-1 configures an aqueous solution of piperazine and sodium dodecyl benzene sulfonate as the first solution; configures a solution of trimesoyl chloride in n-hexane as the second solution; S3-2 immerses the second surface of the porous substrate in the first solution, takes out after immersing for a set time, immerses in the second solution to perform a polymerization reaction, generates a polymer on the second surface, and obtains a nanofiltration layer.

7. The method of claim 6, wherein: In S3-1, the mass fraction of piperazine in the first solution is 0.1-5wt%, and the mass fraction of sodium dodecyl benzene sulfonate is 0.1-3.6mmol / L; The mass fraction of trimesoyl chloride in the second solution is 0.05-0.3wt%.

8. Use of a photothermal driven ionic separation device, characterized in that: The ion separation device driven by photothermal is used to extract ions in a solution, the ion separation device driven by photothermal floats on the solution, and the ion separation membrane is in contact with the solution.

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