Crown ether / graphene oxide photo-thermal ion separation membrane as well as preparation method and application thereof

Abstract

The invention discloses a crown ether / graphene oxide photo-thermal ion separation membrane. The crown ether / graphene oxide photo-thermal ion separation membrane comprises a photo-thermal evaporation layer and an ion separation layer, a vertical porous channel is arranged on the photo-thermal evaporation layer; the ion separation layer is arranged on one side of the photo-thermal evaporation layer. The ion separation layer can separate ions in a solution through the aperture screening effect of crown ether, so that the required single ion passes through the ion separation layer, and all the remaining ions are intercepted. The photo-thermal evaporation layer is arranged on the ion separation layer, is composed of vertical porous channels with a photo-thermal conversion effect, can generate megapascal pressure, and drives water to drive ions to be separated to penetrate through the ion separation layer to the photo-thermal evaporation layer for photo-thermal evaporation, so that ion separation is realized. The separation membrane not only can be used for separating lithium ions and various other ions in a salt lake solution to realize selective recovery of the lithium ions, but also can be used for separating other ions with different radiuses or different charges.

Description

Technical Field

[0001] The invention belongs to the field of ion separation, and specifically relates to a crown ether / graphene oxide photothermal ion separation membrane and a preparation method and application thereof. Background Art

[0002] Lithium (Li), as one of the most valuable resources in the 21st century, is experiencing a sharp increase in demand. On land, salt lake brine has become the main source of lithium, accounting for 70% of recoverable lithium reserves, and plays a vital role in ensuring the healthy development of the lithium battery market. However, lithium ions (Li + ) is abundant, but its concentration is relatively low and is often accompanied by high concentrations of magnesium ions (Mg 2+ ) and a large amount of sodium ions (Na + ), potassium ion (K + ) and other monovalent interfering ions. In the lithium extraction process, especially in the final precipitation step, Li + It is usually recovered in the form of hydroxide or carbonate compounds. However, since Mg(OH)2 or MgCO3 also have low solubility, co-precipitation often occurs during the precipitation process, thus affecting the purity of the final product. In addition, monovalent interfering ions will also be encapsulated and co-precipitated during precipitation, resulting in reduced product purity. Therefore, how to achieve Li before precipitation treatment? + With Mg 2+ and other Na + , K + The efficient and selective separation of monovalent interfering ions has become the key to obtaining high-purity lithium products.

[0003] Although the traditional lithium extraction process based on solar evaporation / precipitation can meet the demand to a certain extent, it requires the use of a large amount of chemicals and is not suitable for lithium ions with high Mg content. 2+ / Li + Mass ratio (MLR) brine treatment is not effective. In contrast, the nanofiltration (NF) process has attracted much attention for its selective separation ability of ions. Nanofiltration membranes can distinguish ions of different valence states and sizes to a certain extent, achieving Li + With Mg 2+ However, due to the high ionic strength of salt lake water, complex raw material composition, and operational problems such as easy scaling, direct nanofiltration technology for lithium extraction faces major challenges. + With Mg 2+ The separation is more effective, but for other ions with similar charge and ionic radius, Na + , K +In order to overcome these difficulties, nanofiltration is usually combined with other pretreatment and post-treatment units to form a complete treatment process. In the pretreatment stage, a series of chemical precipitation or ion exchange methods are used to separate the Li + Pre-enrichment and try to remove or reduce Na + , K + The treated brine is then diluted to a certain ratio and enters the nanofiltration process module to reduce the magnesium-lithium ratio and highly enrich Li + In the nanofiltration process, the Li + In the post-processing stage, the reverse osmosis membrane treatment process module is used to concentrate the permeate from the nanofiltration process module to recover the Li + It is used for the final precipitation step, and clean water is recovered at the same time for dilution of high-concentration brine in the pretreatment stage. Although this integrated nanofiltration treatment process has improved the extraction efficiency of lithium to a certain extent, its process flow is complicated, the operation is cumbersome, and the equipment and facilities involved in the pressure-driven membrane treatment process section (such as nanofiltration membrane and reverse osmosis membrane treatment unit) have high investment costs and great energy consumption. In addition, the separation efficiency for monovalent ions (such as sodium and potassium) still needs to be further improved. Therefore, how to further optimize the lithium extraction process, reduce energy consumption and cost, and ultimately achieve the one-step nanofiltration simultaneous removal of divalent magnesium ions and monovalent sodium and potassium ions has become a problem that needs to be solved urgently. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a crown ether / graphene oxide photothermal ion separation membrane that can separate lithium and other ions in a salt lake solution, and separate other ions with different radii or different charges; another purpose of the present invention is to provide a preparation method and application of the crown ether / graphene oxide photothermal ion separation membrane.

[0005] Technical solution: The crown ether / graphene oxide photothermal ion separation membrane of the present invention comprises a photothermal evaporation layer and an ion separation layer; the photothermal evaporation layer is provided with vertical porous channels; the ion separation layer is provided on one side of the photothermal evaporation layer. The photothermal evaporation layer absorbs light and converts it into heat; the ion separation layer selectively transmits the ions to be separated.

[0006] Preferably, the photothermal evaporation layer is an AAO membrane containing a light-absorbing material, the light-absorbing material is coated in the pores of the AAO membrane, the AAO membrane is an anodized aluminum template with a pore size of 10 to 100 nm; the light-absorbing material is at least one of polyaniline and polypyrrole. The AAO membrane has vertical porous channels with adjustable pore size, has hydrophilic properties, and has the advantage of adjustable hydrophilic properties. After the organic polymer light-absorbing material is compounded with the AAO membrane, the photothermal evaporation layer can have the function of absorbing light and converting it into heat.

[0007] Preferably, the ion separation layer comprises graphene oxide nanosheets providing mass transfer channels and crown ethers providing lithium ion specific recognition in the mass transfer channels; the crown ether is at least one of benzo-9-crown-3, benzo-12-crown-4, and dibenzo-14-crown-4.

[0008] Preferably, the mass fraction of the crown ether in the ion separation layer relative to the graphene oxide solution is 0.1 to 2 wt %, and more preferably 0.5 wt %.

[0009] Preferably, the porous channels on the photothermal evaporation layer have a pore size of 10 to 100 nm, and more preferably the channels have an average pore size of 50 nm.

[0010] Preferably, the photothermal evaporation layer has a thickness of 100-200 μm and a porosity of 10-30%, preferably 15-20%; the water contact angle of the photothermal evaporation layer is 10-30°, more preferably 16°.

[0011] Preferably, the thickness of the ion separation layer is 1-5 μm, more preferably 2 μm.

[0012] Preferably, the graphene oxide sheet has a diameter of 0.5 to 5 μm.

[0013] Preferably, the photothermal evaporation layer and the ion separation layer are formed as an integral structure, and the ion separation layer is prepared by vacuum filtration on one side of the photothermal evaporation layer; this arrangement is conducive to the capillary force of the photothermal evaporation layer to fully act on the ion separation layer, thereby achieving effective transmission of water and ions.

[0014] Preferably, the crown ether / graphene oxide photothermal ion separation membrane is used to separate ions in an aqueous solution, more preferably to separate ions of different valence states, and further preferably to separate lithium ions from all other monovalent ions and divalent ions.

[0015] The method for preparing the crown ether / graphene oxide photothermal evaporation separation membrane of the present invention comprises the following steps:

[0016] (1) Preparing a photothermal evaporation layer: preparing a light-absorbing material monomer into an aqueous solution, immersing an AAO membrane in the solution, and fully absorbing the light-absorbing material monomer in the pores of the AAO membrane; the light-absorbing material monomer is at least one of pyrrole and aniline; preparing an oxidant aqueous solution, immersing the AAO membrane that has fully absorbed the light-absorbing material monomer into the oxidant aqueous solution, and the light-absorbing material monomer is chemically oxidized and polymerized in the pores of the AAO membrane to generate a light-absorbing material; and cleaning the AAO membrane coated with the light-absorbing material to obtain a photothermal evaporation layer;

[0017] (2) Using the photothermal evaporation layer as a substrate, an ion separation layer is prepared on one side of the photothermal evaporation layer: a graphene oxide aqueous solution is prepared as a first solution; a crown ether dimethylformamide solution is prepared as a second solution; the first solution and the second solution are mixed and ultrasonicated until they are uniformly dispersed to obtain a mixed solution; the photothermal evaporation layer is used as a filter membrane, and the mixed solution is filtered thereon to obtain an ion separation layer.

[0018] The ion separation layer prepared by this method is an integrated structure with the photothermal evaporation layer. The ion separation layer has specific nanopores and crown ether Li + Specific recognition site enables it to effectively intercept Mg in the salt solution 2+ 、Na + , K + Interfering impurity ions such as Li + As water flows through the internal nanopores and migrates upward, Li + Enriched inside and on the surface of the evaporation / mass transfer mixing layer.

[0019] Preferably, the mass fraction of the aqueous solution of the light absorbing material monomer is 0.5-2wt%.

[0020] Preferably, the oxidant is one of benzoyl peroxide, ammonium dichromate, hydrogen peroxide, ferric chloride, and ammonium persulfate.

[0021] Preferably, the mass fraction of the aqueous oxidant solution is 3.5-10wt%.

[0022] Preferably, the mass fraction of the aqueous solution of graphene oxide in the first solution is 1-2 mg / ml, and the mass fraction of the crown ether in the second solution is 10-200 mg / ml; the mixing mass ratio of the first solution to the second solution is (10-20): (1-5).

[0023] Preferably, the mass fraction of the crown ether is 50 mg / ml.

[0024] As a preferred embodiment, the preparation method of the photothermal evaporation layer is as follows: a main body of an AAO template porous membrane is selected, an organic polymer light-absorbing material is selected to be mixed with the AAO template to form a porous membrane, and the following steps are performed: (1) an organic polymer monomer and an oxidant are mixed in a solvent in a set amount to form a mixed solution; (2) the AAO membrane is immersed in the solution, and the light-absorbing material monomers such as pyrrole and aniline are fully adsorbed on the surface of the AAO membrane. Preferably, the immersion time is 2 minutes; (3) after the immersion of the polymer monomer is completed, the AAO membrane is immersed in an ammonium persulfate aqueous solution to generate light-absorbing materials such as polyaniline or polypyrrole through chemical oxidation polymerization; (4) the AAO membrane coated with polyaniline or polypyrrole is then immersed in water for washing for multiple times to finally obtain the photothermal evaporation layer.

[0025] Preferably, the organic polymer light-absorbing material is polypyrrole, the content of which in the mixed solution is in the range of 0.5-2wt%, and the mass fraction of the ammonium persulfate aqueous solution is 3.5-10wt%. Ammonium persulfate dissociates into sulfate ions (SO4 2 ) and persulfate ions (S2O 2 ). Persulfate has a strong oxidizing property and can oxidize pyrrole monomers. When the pyrrole monomer comes into contact with APS, the persulfate ion oxidizes the pyrrole monomer into a radical cation. The radical cations of the oxidized pyrrole monomer will combine with each other to form long-chain polypyrrole (PPy) molecules through a conjugated system. When the pyrrole monomer and APS solution are immersed in the AAO template, the pyrrole monomer will penetrate into the nanopores of the AAO. The oxidative polymerization reaction occurs inside the pores, and PPy is gradually deposited in the pores. On the one hand, the polymer is deposited in the pores and partially fills the pores, so the effective pore size becomes smaller. As the amount of polymer increases, the actual diameter of the pores gradually decreases, which is conducive to regulating the pore size of the final photothermal evaporation layer to produce a megapascal pressure. On the other hand, since part of the pores are filled with polypyrrole, the porosity will decrease and the pore size distribution of the AAO membrane will become narrower (the pore size distribution is more uniform).

[0026] As a preferred embodiment, the ion separation layer is prepared by: (1) preparing a graphene oxide aqueous solution containing 1-2 mg / ml and a dimethylformamide solution containing 10-200 mg / ml of benzo-12-crown ether-4; (2) mixing the two in a ratio of (10-20):(1-5) at 20-40°C for 1-5 hours to obtain a completely dispersed mixed solution; (3) using the prepared photothermal evaporation layer as a filter membrane, filtering 5-20 ml of the mixed solution through a solvent filter, and filtering until the surface is completely dried; (4) removing the filtered filter membrane from the solvent filter, and vacuum drying at 50-60°C for 4-12 hours to obtain an ion separation layer.

[0027] Application of the crown ether / graphene oxide photothermal ion separation membrane of the present invention in lithium extraction from salt lakes.

[0028] Preferably, the specific application method is: placing the crown ether / graphite oxide photothermal evaporation ion separation membrane in a lithium-containing solution, the photothermal evaporation layer is hydrophilic, and under the capillary force provided by the photothermal evaporation layer, the ion separation layer intercepts divalent magnesium ions and monovalent sodium ions and potassium ions, water and lithium ions pass through the ion separation layer to the photothermal evaporation layer, water evaporates in the photothermal evaporation layer, and lithium ions are deposited in the pores or on the surface of the photothermal evaporation layer.

[0029] Preferably, in order to make the ion separation membrane float on the liquid surface, the ion separation membrane is encapsulated between two O-type rubber gaskets, which not only play a supporting role but also provide buoyancy, so that the entire device floats on the liquid surface and ensures that the ion separation layer is in contact with the solution.

[0030] Principle of the invention: The crown ether / graphene oxide photothermal ion separation membrane of the present invention can not only be used to separate lithium and other ions in salt lake solutions to achieve lithium extraction, but also can be used to separate other ions with different radii or different charges. The solution targeted can be an aqueous solution or an organic solution. The separation membrane includes a photothermal evaporation layer and an ion separation layer. The ion separation layer can separate ions in the solution through the pore structure and the ion recognition mechanism of the crown ether, so that the required ions pass through the ion separation layer and the remaining ions are intercepted. The photothermal evaporation layer is provided with nano-scale vertical porous channels and has good compatibility with solvents. If the solution is an aqueous solution, the photothermal evaporation layer is a hydrophilic material. If the solution is an organic solution, the photothermal evaporation layer is organic solvent-friendly. The porous channels in the photothermal evaporation layer can generate capillary forces above megapascals, driving water to drive the ions to be separated through the ion separation layer to the photothermal evaporation layer. When in use, the lower surface of the ion separation layer (the side facing away from the photothermal evaporation layer) contacts the solution, and the photothermal evaporation layer is placed above the liquid surface of the solution, absorbs light and converts it into heat, heats the water entering the photothermal evaporation layer and converts it into water vapor or heats the organic solvent and converts it into gas to escape into the air, leaving the desired ions and depositing them in the porous channels of the photothermal evaporation layer or on the upper surface of the photothermal evaporation layer. After the ions accumulate to a certain amount, the ions in the photothermal evaporation layer are removed by soaking, scraping or other methods.

[0031] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0032] (1) The ion separation membrane of the present invention provides the driving force for ion or solute transport through interfacial photothermal evaporation, and utilizes the capillary negative pressure of hundreds of MPa generated during the photothermal evaporation of liquid in the capillary channel to drive the underlying nanofiltration membrane, thereby achieving selective ion separation without the need for external energy consumption; this technology not only has the advantage of being green and environmentally friendly, but also significantly reduces operating costs; in addition, through the photothermal effect, the integrated photothermal evaporation-separation membrane can directly collect lithium salt crystals on the membrane surface, which greatly improves the salt concentration capacity compared to traditional membrane separation technology, thereby realizing an efficient, clean, low-cost, and renewable salt lake lithium extraction process.

[0033] (2) The ion separation membrane of the present invention can directly treat salt lake brine with a high magnesium-lithium ratio and multiple interfering ions, and improve the Na + , K + One-step synchronous separation finally collects high-purity lithium salt crystals on the surface of the separation membrane and can achieve long-term stable operation; lithium salt crystals can be recycled and collected, and are economical and efficient, which further improves the renewability and economy of lithium extraction from salt lakes.

[0034] (3) The photothermal evaporation layer of the present invention integrates photothermal conversion, evaporation and transmission functions, and can be precisely controlled according to the specific properties of the feed solution (such as the salt ion concentration and the lithium-magnesium content ratio in the solution). By adjusting the photothermal conversion rate, pore size and hydrophilicity, the evaporation layer can flexibly adapt to solutions of different properties, ensuring efficient evaporation and separation effects, and improving the system's adaptability and separation performance to a variety of solution environments.

[0035] (4) The ion separation layer of the present invention can be prepared in situ on either side of the photothermal evaporation layer to form an integrated structure, thereby ensuring lossless transmission of capillary force.

[0036] (5) The ion separation membrane of the present invention is not only lightweight and ultra-thin (less than 0.5 mm in thickness) for portability, but is also suitable for large-scale production, further improving the breadth of application and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The structure diagram of the crown ether / graphene oxide photothermal ion separation membrane of the present invention, 1 is the photothermal evaporation layer, 2 is the ion separation layer;

[0038] Figure 2 It is a curve diagram of water evaporation rate of the crown ether / graphene oxide photothermal ion separation membrane in salt solutions of various concentrations in Example 1 of the present invention;

[0039] Figure 3 are the separation factors of lithium magnesium, lithium potassium and lithium sodium of the crown ether / graphene oxide photothermal ion separation membrane in Example 1 of the present invention in salt solutions of various concentrations;

[0040] Figure 4 is the crystallization rate of lithium chloride of the crown ether / graphene oxide photothermal ion separation membrane in Example 1 of the present invention in salt solutions of various concentrations;

[0041] Figure 5 The separation factors of lithium magnesium, lithium potassium and lithium sodium in 1 g / L salt solution of the crown ether / graphene oxide photothermal ion separation membrane in Example 1 of the present invention and the pure graphene oxide membrane in Comparative Example 1 of the present invention;

[0042] Figure 6 It is the lithium chloride crystallization rate of the crown ether / graphene oxide photothermal ion separation membrane in Example 1 of the present invention and the pure graphene oxide membrane in Comparative Example 1 of the present invention in 1 g / L salt solution. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0044] The crown ether / graphene oxide photothermal ion separation membrane of the present invention (such as Figure 1 The photothermal evaporation layer 1 includes a photothermal evaporation layer 1 and an ion separation layer 2. The photothermal evaporation layer 1 is provided with densely arranged vertical nanoscale channels, which can generate strong capillary forces. The photothermal evaporation layer 1 is made of hydrophilic material. Under the action of capillary forces, water flows upward along the channels, ensuring efficient water transmission and evaporation process.

[0045] The ion separation layer 2 achieves a selective ion separation function by regulating the pore size and / or the crown ether mass fraction. This layer allows specific ions to pass through and intercepts other ions. In this embodiment, the ion separation layer 2 can selectively pass lithium ions while effectively intercepting divalent magnesium ions and monovalent sodium ions and potassium ions, thereby achieving precise ion separation.

[0046] During use, the double-layer structure is fixedly connected along the four sides of the membrane by rubber gaskets, so that the ion separation membrane floats on the surface of the solution. The photothermal evaporation layer 1 is located in the upper layer, and the ion separation layer 2 is located in the lower layer. The ion separation layer 2 is in direct contact with the solution and is used to separate lithium ions and other interfering impurity ions in the solution. During the separation process, lithium ions pass through the ion separation layer and are deposited in the form of salt crystals on the top of the photothermal evaporation layer 1, while magnesium ions, sodium ions, and potassium ions are partially or mostly blocked and cannot pass through the ion separation layer 2. Finally, high-purity lithium ion crystals can be obtained by scraping or flushing the top of the evaporation / mass transfer mixed layer, and the device can be used to cyclically extract lithium salt crystals to further improve the recovery efficiency.

[0047] The device has a simple structure and excellent ion selective separation performance. Through the small aperture channel and efficient photothermal conversion capability of the photothermal evaporation layer 1, the device can collect concentrated lithium salt crystals directly on the top of the photothermal evaporation layer 1 under the drive of solar energy, achieving efficient lithium ion separation and recovery.

[0048] Example 1

[0049] The preparation method of the crown ether / graphene oxide photothermal ion separation membrane comprises the following steps:

[0050] S01 Preparation of photothermal evaporation layer:

[0051] (1) preparing an aqueous solution containing 1 wt% pyrrole, and immersing an AAO membrane with a pore size of 100 nm in the pyrrole aqueous solution for 2 min, so that the pyrrole monomer is fully adsorbed on the surface of the AAO membrane;

[0052] (2) preparing an ammonium persulfate oxidant into an aqueous solution with a mass fraction of 3.5 wt%, and then immersing the AAO membrane fully adsorbing the pyrrole monomer in the ammonium persulfate aqueous solution for 2 minutes, so that the pyrrole monomer is polymerized in the AAO membrane by chemical oxidation to generate a polypyrrole polymer light-absorbing material;

[0053] (3) immersing the AAO film coated with the polypyrrole polymer light-absorbing material in water and washing it multiple times to obtain a photothermal evaporation layer;

[0054] S02 Preparation of ion separation layer:

[0055] (1) preparing an aqueous solution containing 1 mg / ml graphene oxide, and magnetically stirring at 25° C. for 4 h to obtain a completely dispersed and uniform graphene oxide aqueous solution;

[0056] (2) preparing a dimethylformamide solution containing 50 mg / ml of benzo-12-crown-4, and stirring magnetically at 25° C. for 4 h to obtain a dimethylformamide solution in which benzo-12-crown-4 was completely dissolved;

[0057] (3) mixing the graphene oxide aqueous solution and the benzo-12-crown-4-dimethylformamide solution in a mass ratio of 10:1, and magnetically stirring at 25° C. for 4 h to obtain a uniformly mixed solution;

[0058] (4) Take 10 ml of the mixed solution, use the prepared photothermal evaporation layer as the substrate, and perform vacuum filtration in a solvent filter until the surface water is completely drained;

[0059] (5) The filtered membrane was peeled off from the solvent filter and vacuum dried at 60° C. for 12 h to obtain a crown ether / graphene oxide crown ether / graphene oxide photothermal ion separation membrane.

[0060] Example 2

[0061] The preparation method of the crown ether / graphene oxide photothermal ion separation membrane comprises the following steps:

[0062] S01 Preparation of photothermal evaporation layer:

[0063] (1) preparing an aqueous solution containing 2 wt% aniline, and immersing an AAO membrane with a pore size of 50 nm in the aqueous solution of aniline for 2 min, so that the aniline monomer is fully adsorbed on the surface of the AAO membrane;

[0064] (2) preparing an ammonium persulfate oxidant into an aqueous solution with a mass fraction of 10 wt%, and then immersing the AAO membrane that has fully adsorbed the aniline monomer in the ammonium persulfate aqueous solution for 2 minutes, so that the aniline monomer is chemically oxidized and polymerized in the AAO membrane to generate a polyaniline polymer light-absorbing material;

[0065] (3) immersing the AAO film coated with the polyaniline polymer light-absorbing material in water and washing it multiple times to obtain a photothermal evaporation layer;

[0066] S02 Preparation of ion separation layer:

[0067] (1) preparing an aqueous solution containing 1.5 mg / ml graphene oxide, and magnetically stirring at 25° C. for 4 h to obtain a completely dispersed and uniform graphene oxide aqueous solution;

[0068] (2) preparing a dimethylformamide solution containing 10 mg / ml dibenzo-14-crown-4, and stirring magnetically at 25° C. for 4 h to obtain a dimethylformamide solution in which dibenzo-14-crown-4 is completely dissolved;

[0069] (3) mixing the graphene oxide aqueous solution and the dibenzo-14-crown-4-dimethylformamide solution in a mass ratio of 10:5, and magnetically stirring at 25° C. for 4 h to obtain a uniformly mixed solution;

[0070] (4) Take 10 ml of the mixed solution, use the prepared photothermal evaporation layer as the substrate, and perform vacuum filtration in a solvent filter until the surface water is completely drained;

[0071] (5) The filtered membrane was peeled off from the solvent filter and vacuum dried at 60° C. for 12 h to obtain a crown ether / graphene oxide crown ether / graphene oxide photothermal ion separation membrane.

[0072] Example 3

[0073] The preparation method of the crown ether / graphene oxide photothermal ion separation membrane comprises the following steps:

[0074] S01 Preparation of photothermal evaporation layer:

[0075] (1) preparing an aqueous solution containing 0.5 wt% pyrrole and aniline (mass fraction ratio is 1:1), immersing an AAO membrane with a pore size of 10 nm in the aqueous solution of pyrrole and aniline for 2 min, so that the pyrrole and aniline monomers are fully adsorbed on the surface of the AAO membrane;

[0076] (2) preparing an ammonium persulfate oxidant into an aqueous solution with a mass fraction of 7 wt%, and then immersing the AAO membrane fully adsorbing pyrrole and aniline monomers in the ammonium persulfate aqueous solution for 2 minutes, so that the pyrrole and aniline monomers are chemically oxidized and polymerized in the AAO membrane to generate polypyrrole and polyaniline polymer light-absorbing materials;

[0077] (3) immersing the AAO film coated with polypyrrole and polyaniline polymer light-absorbing materials in water and washing it multiple times to obtain a photothermal evaporation layer;

[0078] S02 Preparation of ion separation layer:

[0079] (1) preparing an aqueous solution containing 2 mg / ml graphene oxide, and magnetically stirring at 25° C. for 4 h to obtain a completely dispersed and uniform graphene oxide aqueous solution;

[0080] (2) preparing a dimethylformamide solution containing 200 mg / ml of benzo-9-crown-3, stirring under magnetic stirring at 25° C. for 4 h, to obtain a dimethylformamide solution of completely dissolved benzo-9-crown-3;

[0081] (3) mixing the graphene oxide aqueous solution and the benzo(9-crown-3-dimethylformamide) solution in a mass ratio of 20:5, and magnetically stirring at 25° C. for 4 h to obtain a uniformly mixed solution;

[0082] (4) Take 10 ml of the mixed solution, use the prepared photothermal evaporation layer as the substrate, and perform vacuum filtration in a solvent filter until the surface water is completely drained;

[0083] (5) The filtered membrane was peeled off from the solvent filter and vacuum dried at 60° C. for 12 h to obtain a crown ether / graphene oxide crown ether / graphene oxide photothermal ion separation membrane.

[0084] Comparative Example 1

[0085] It only contains an ion separation layer but no photothermal evaporation layer, that is, no light-absorbing material is added to the pores of the AAO membrane, and no crown ether molecules are introduced into the ion separation layer.

[0086] Comparative Example 1 The preparation steps are as follows:

[0087] (1) preparing an aqueous solution containing 1 mg / ml graphene oxide, and magnetically stirring at 25° C. for 4 h to obtain a completely dispersed and uniform graphene oxide aqueous solution;

[0088] (2) taking 10 ml of graphene oxide aqueous solution, using an AAO membrane with a pore size of 100 nm as the substrate, and vacuum filtering in a solvent filter until the surface water is completely drained;

[0089] (3) The filtered membrane was peeled off from the solvent filter and vacuum dried at 60° C. for 12 h to obtain the ion separation membrane of Comparative Example 1.

[0090] test:

[0091] Prepare the following solution:

[0092] Solution 1: The salt solution is a mixed salt solution of magnesium chloride, sodium chloride, potassium chloride and lithium chloride with a total concentration of 1 g / L, wherein the mass ratio of each ion is 1:1:1:1.

[0093] Solution two:

[0094] The salt solution is a mixed salt solution of magnesium chloride, sodium chloride, potassium chloride and lithium chloride with a total concentration of 2 g / L, wherein the mass ratio of each ion is 1:1:1:1.

[0095] Solution three:

[0096] The salt solution is a mixed salt solution of magnesium chloride, sodium chloride, potassium chloride and lithium chloride with a total concentration of 3 g / L, wherein the mass ratio of each ion is 1:1:1:1.

[0097] Solution four:

[0098] The salt solution is a mixed salt solution of magnesium chloride, sodium chloride, potassium chloride and lithium chloride with a total concentration of 4 g / L, wherein the mass ratio of each ion is 1:1:1:1.

[0099] Solution 5:

[0100] The salt solution is a mixed salt solution of magnesium chloride, sodium chloride, potassium chloride and lithium chloride with a total concentration of 5 g / L, wherein the mass ratio of each ion is 1:1:1:1.

[0101] The above solutions were poured into square containers with dimensions of 20 cm × 20 cm × 10 cm, and the crown ether / graphene oxide photothermal ion separation membrane prepared in Example 1 was placed on the surface of the solution in the corresponding container, ensuring that the crown ether / graphene oxide photothermal ion separation membrane floated above the solution and the ion separation layer was in contact with the solution. Due to the presence of nanoscale pores in the photothermal evaporation layer, a capillary force of 100 MPa was generated, and the pressure was transmitted to the ion separation layer, thereby driving the filtration process of the membrane and selectively intercepting Mg. 2+ 、Na + , K + , and allow Li +The lithium ions finally crystallize and precipitate on the top of the photothermal evaporation layer. The lithium salt crystals can be collected directly by brushing, or collected by washing and dissolving. The test time is 72 hours. Under the irradiation of 1 sun intensity, lithium salt crystals precipitate on the top of the photothermal evaporation layer.

[0102] The water evaporation rate, separation factor and lithium chloride crystallization rate of Example 1 in each square container were tested. The results are as follows: Figure 2 , Figure 3 and Figure 4 As shown. Figure 2 and Figure 3 It can be seen that with the increase of the concentration of the mixed brine solution, the water evaporation rate and the separation factor remain basically unchanged, indicating that the crown ether / graphene oxide photothermal ion separation membrane can maintain a stable separation efficiency in salt solutions of different concentrations, and the separation performance is not significantly affected by the salt concentration. Figure 4 It shows that with the increase of the concentration of the mixed brine solution, the crystallization rate of lithium chloride increases significantly, indicating that high-concentration salt solutions help to accelerate the crystallization process of lithium chloride. Among them, the calculation method of the separation factor is: separation factor = ratio of ion mass after separation / ratio of ion mass before separation. Taking the mass ratio of lithium and magnesium ions in the mixed solution to be separated as 1:1 as an example, if the mass ratio of lithium and magnesium ions measured in the salt reservoir after separation is 10:1 (which can be measured by inductively coupled plasma spectrometry), the separation factor is (10:1) / (1:1)=10.

[0103] The crystallization rate of lithium chloride is defined as the mass of lithium chloride powder collected at the top of the photothermal evaporation layer by the interfacial evaporation driven by solar energy per unit area of ​​the separation membrane per unit time. In the present invention, the salt crystal powder collected at the top of the photothermal evaporation layer is first dissolved in a certain volume of aqueous solution, and the mass concentration of lithium ions in the aqueous solution is measured by an inductively coupled plasma spectrometer. For example, if the lithium ion concentration is measured to be 1 mg / L, assuming that the volume of the aqueous solution is 0.1 L, it can be known that the mass of lithium in the salt crystals collected at the top of the evaporation / mass transfer mixed layer is 0.1 mg. According to the molar mass ratio of lithium chloride, the mass is converted into the mass of lithium chloride, and then divided by the effective working area and working time of the separation membrane to obtain the crystallization rate of lithium chloride.

[0104] The separation factor and lithium chloride crystallization rate of comparative example 1 were tested using solution 1. The results are as follows: Figure 5 and Figure 6 As shown. Figure 5 It can be seen that since comparative example 1 does not add a crown ether with a specific recognition function for lithium ions, it only has a limited separation effect on magnesium ions, and has no separation effect on sodium ions and potassium ions, and the separation factor is close to 1. Example 1 has a good separation effect on all ions. Figure 6It can be seen that due to the absence of the photothermal evaporation layer, the crystallization rate of lithium chloride in Comparative Example 1 is much lower than that in Example 1.

Claims

1. A crown ether / graphene oxide photothermal ion separation membrane, characterized in that: It comprises a photothermal evaporation layer and an ion separation layer; the photothermal evaporation layer is provided with a vertical porous channel; the ion separation layer is arranged on one side of the photothermal evaporation layer.

2. The crown ether / graphene oxide photothermal evaporation separation membrane according to claim 1, characterized in that: The photothermal evaporation layer is an AAO film containing a light-absorbing material, the light-absorbing material is coated in the pores of the AAO film, and the AAO film is an anodized aluminum template with a pore size of 10 to 100 nm; the light-absorbing material is at least one of polyaniline and polypyrrole.

3. The crown ether / graphene oxide photothermal evaporation separation membrane according to claim 1, characterized in that: The ion separation layer comprises graphene oxide nanosheets and crown ethers; the crown ether is at least one of benzo-9-crown-3, benzo-12-crown-4, and dibenzo-14-crown-4.

4. The crown ether / graphene oxide photothermal ion separation membrane according to claim 1, characterized in that: The photothermal evaporation layer has a thickness of 100-200 μm and a porosity of 10-30%; and a water contact angle of the photothermal evaporation layer is 10-30°.

5. The crown ether / graphene oxide photothermal evaporation separation membrane according to claim 1, characterized in that: The thickness of the ion separation layer is 1-5 μm; the diameter of the graphene oxide sheet is 0.5-5 μm.

6. The crown ether / graphene oxide photothermal ion separation membrane according to claim 1, characterized in that: The photothermal evaporation layer and the ion separation layer are formed as an integral structure, and the ion separation layer is prepared by vacuum filtration on one side of the photothermal evaporation layer.

7. A method for preparing the crown ether / graphene oxide photothermal evaporation separation membrane according to claim 1, comprising the following steps: (1) Preparing a photothermal evaporation layer: preparing a light-absorbing material monomer into an aqueous solution, immersing an AAO membrane in the solution, and fully absorbing the light-absorbing material monomer in the pores of the AAO membrane; the light-absorbing material monomer is at least one of pyrrole and aniline; preparing an oxidant aqueous solution, immersing the AAO membrane that has fully absorbed the light-absorbing material monomer into the oxidant aqueous solution, and the light-absorbing material monomer is chemically oxidized and polymerized in the pores of the AAO membrane to generate a light-absorbing material; Cleaning the AAO film coated with the light absorbing material to obtain a photothermal evaporation layer; (2) Using the photothermal evaporation layer as a substrate, an ion separation layer is prepared on one side of the photothermal evaporation layer: a graphene oxide aqueous solution is prepared as a first solution; a crown ether dimethylformamide solution is prepared as a second solution; the first solution and the second solution are mixed and ultrasonicated until they are uniformly dispersed to obtain a mixed solution; the photothermal evaporation layer is used as a filter membrane, and the mixed solution is filtered thereon to obtain an ion separation layer.

8. The method for preparing the crown ether / graphene oxide photothermal ion separation membrane according to claim 7, characterized in that: The mass fraction of the aqueous solution of graphene oxide in the first solution is 1-2 mg / ml, and the mass fraction of the crown ether in the second solution is 10-200 mg / ml; the mixing mass ratio of the first solution to the second solution is (10-20): (1-5).

9. Use of the crown ether / graphene oxide photothermal ion separation membrane according to claim 1 in lithium extraction from salt lakes.

10. The use according to claim 9, characterized in that: The specific application method is: placing the crown ether / graphite oxide photothermal evaporation ion separation membrane in a lithium-containing solution, the photothermal evaporation layer is hydrophilic, and under the capillary force provided by the photothermal evaporation layer, the ion separation layer intercepts divalent magnesium ions and monovalent sodium ions and potassium ions, water and lithium ions pass through the ion separation layer to the photothermal evaporation layer, water evaporates in the photothermal evaporation layer, and lithium ions are deposited in the pores or on the surface of the photothermal evaporation layer.

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