Biomimetic two-dimensional mica membranes for specific transmission and method for their production + Biomimetic two-dimensional mica membranes for specific transmission and method for their production

Abstract

The application belongs to the field of separation membrane materials, and particularly relates to a biomimetic two-dimensional vermiculite membrane for K + Specific transport biomimetic two-dimensional vermiculite membrane and preparation method thereof. The biomimetic two-dimensional vermiculite membrane for K + Specific transport biomimetic two-dimensional vermiculite membrane and preparation method thereof. The biomimetic two-dimensional vermiculite membrane for K + Specific transport biomimetic two-dimensional vermiculite membrane and preparation method thereof. The biomimetic two-dimensional vermiculite membrane for K + Under the driving of ion concentration difference, a strong affinity relationship is formed with carbonyl functional groups of PAM polymers in the channel;K + Jumping along the polymer chain, a knock on effect is generated. Therefore, the ion channel membrane exhibits excellent K + The permeation rate of the biomimetic two-dimensional vermiculite membrane is 16 times that of Na + , and has a high permeation rate of 297 mmol m ‑2 h ‑1 . The biomimetic two-dimensional vermiculite membrane provides a substitution strategy for K + separation membranes.

Description

Technical Field

[0001] This invention belongs to the field of separation membrane materials, specifically relating to K + A biomimetic two-dimensional vermiculite film for specific transport and its preparation method. Background Technology

[0002] Potassium is one of the three essential nutrients for plant growth. It exists in ionic form and dissolves in plant sap, directly affecting crop growth. Simultaneously, potassium ions are also one of the most important cations in human and animal cells, directly impacting animal and human health. Therefore, the chemical production of potassium-containing compounds is crucial for agriculture and biomedicine.

[0003] Oceans and salt lakes possess abundant potassium resources. Potassium is the sixth most abundant mineral in seawater, and its content is even higher in salt lake brines. With the continuous increase in potassium consumption due to global economic development, researching efficient separation and extraction technologies for potassium ions from oceans and salt lakes will be an important direction for the development and utilization of global potassium resources. In potassium extraction from salt lakes and potassium enrichment from seawater, sodium ions are the most common associated ions, and a common problem encountered is sodium... + / K + Separation. Traditional separation methods include chemical precipitation, extraction, adsorption, and ion exchange; however, these methods all have some drawbacks, such as high energy consumption, poor adsorption and separation capacity, poor specificity and selectivity, and cumbersome processes. Therefore, researchers are still dedicated to developing new, efficient, and selective methods, processes, and materials for the separation of potassium ions.

[0004] In recent years, two-dimensional materials, such as graphene / graphene oxide (GO), transition metal sulfides (TMDs), two-dimensional MOF / COF, two-dimensional molecular sieves, and MXene, have demonstrated excellent performance in separation membranes due to their unique physicochemical properties, showing promising prospects in the field of separation. Two-dimensional membranes, formed by stacking two-dimensional nanomaterials, are a novel type of membrane with a layered structure, where mass transfer channels are generally the interlayer cavities between two-dimensional nanosheets. The geometric dimensions of two-dimensional membrane channels are close to those of ion channels in cell membranes. Researchers are attempting to modulate the physicochemical properties of micro-regions within two-dimensional channels to control the transport process of substances within the channels, hoping to achieve highly efficient selective separation of substances within artificial biomimetic membrane channels similar to those in cell membranes. Summary of the Invention

[0005] The object of this invention is to provide a method for K + Biomimetic two-dimensional vermiculite membrane for specific transport.

[0006] Another object of the present invention is to provide a method for preparing the vermiculite film described above.

[0007] Another object of the present invention is to provide the application of the above-mentioned vermiculite film.

[0008] In nature, the potassium ion channel KcsA consists of four identical subunits aggregated to form a four-fold symmetrical complex. A negatively charged carbonyl oxygen atom on each subunit is located at the center of the channel, which is composed of four stacked carbonyl groups, each containing four carbonyl groups, providing four bonding sites for potassium ions: S1, S2, S3, and S4. As potassium ions pass through the KcsA ion channel, they shed their hydration layer and interact strongly with the carbonyl groups on the subunits. Potassium ions are transported within the ion channel via cooperative hopping between the dual-orbital domains (S1, S3) and (S2, S4).

[0009] In order to simulate This invention constructs an artificial ion channel membrane with suitable channel size and similar binding sites using vermiculite nanosheets and linear polyacrylamide polymer as building blocks, and studies the potassium ion mass transfer mechanism within the channel.

[0010] According to a specific embodiment of the present invention, for K + A method for preparing a biomimetic two-dimensional vermiculite film for specific transport includes the following steps:

[0011] (1) Vermiculite nanosheets were dispersed in a polyacrylamide solution and assembled into a membrane to obtain a Ver-PAM composite membrane;

[0012] (2) Immerse the Ver-PAM composite membrane obtained in step (1) in a cationic solution, wash it, and dry it to obtain the vermiculite membrane.

[0013] According to a specific embodiment of the present invention, for K + A method for preparing a biomimetic two-dimensional vermiculite membrane with specific transport, wherein the cation solution includes a monovalent metal ion solution or a divalent metal ion solution.

[0014] According to a specific embodiment of the present invention, for K + A method for preparing a biomimetic two-dimensional vermiculite film for specific transport, wherein the monovalent metal ion solution includes lithium ion solution, sodium ion solution, potassium ion solution or cesium ion solution; and / or, the concentration of the cation solution is 0.01-10 mol / L.

[0015] According to a specific embodiment of the present invention, for K + A method for preparing a biomimetic two-dimensional vermiculite film for specific transport, wherein the divalent metal ion solution includes a magnesium ion solution or a strontium ion solution; and / or, the concentration of the cation solution is 0.01-10 mol / L.

[0016] According to a specific embodiment of the present invention, for K+ The preparation method of biomimetic two-dimensional vermiculite film with specific transmission, in step (1), the mass ratio of vermiculite nanosheets to polyacrylamide is 0.3-60:0.1-180.

[0017] The molecular weight of polyacrylamide ranges from 40kDa to 6000kDa.

[0018] According to a specific embodiment of the present invention, for K + The preparation method of biomimetic two-dimensional vermiculite membrane with specific transport: In step (1), vermiculite nanosheets are dispersed in polyacrylamide solution, and assembled into a membrane by vacuum filtration and drying to obtain Ver-PAM composite membrane.

[0019] According to a specific embodiment of the present invention, for K + The preparation method of biomimetic two-dimensional vermiculite membrane for specific transport, in step (2), the Ver-PAM composite membrane obtained in step (1) is immersed in a cation solution to allow the cations to fully enter the interlayer of the Ver-PAM composite membrane, and then dried after being washed with ultrapure water.

[0020] This invention provides K obtained by the above preparation method. + Biomimetic two-dimensional vermiculite membrane for specific transport.

[0021] This invention also provides a highly efficient method for separating Na. + K + The method involves separating the sample to be treated using a vermiculite membrane obtained by the above preparation method. The sample to be treated is a solution involved in potassium extraction from salt lakes or potassium enrichment of seawater.

[0022] The beneficial effects of this invention are:

[0023] This invention provides a vermiculite film, K + Driven by the difference in ion concentration, a strong affinity is formed between K and the carbonyl functional groups of the PAM polymer in the vermiculite membrane channel. + Jumping along polymer chains generates a knock-on effect. Therefore, vermiculite films with ion channels exhibit excellent Kk... + Transport performance, K + The permeation rate can reach Na + It is 16 times higher than that, reaching 297 mmol / L. -2 h -1 High permeability. The vermiculite membrane of this invention is K. + Separation membranes offer an alternative strategy. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the preparation process of the Ver-PAM membrane.

[0026] Figure 2 An atomic force microscope image of a single-layer vermiculite nanosheet, scale bar: 500 nm.

[0027] Figure 3 This displays the elemental distribution of Ver-PAM. Scale bar: 30 μm.

[0028] Figure 4 The infrared spectra of Ver, PAM, and Ver-PAM are shown.

[0029] Figure 5 The XRD results of Ver membrane and Ver-PAM membrane are compared under dry and wet conditions.

[0030] Figure 6 The XRD results of the ions-Ver-PAM membrane are shown in both dry and wet conditions. (a) ions-Ver-PAM 5.82％ (b)ions-Ver-PAM 11.54％ (c)ions-Ver-PAM 33.93％ ;(d)ions-Ver-PAM 50.03％ .

[0031] Figure 7 The XRD results of the Ver-PAM membrane under different conditions are shown; (a) the Ver-PAM membrane is immersed in Na + (a) XRD results at different times (wet state); (b) XRD results of Ver-PAM membrane immersed in aqueous solutions at different temperatures (dry state); (c) XRD results of Ver-PAM membrane immersed in aqueous solution at pH 5.29.

[0032] Figure 8 Results of water vapor permeation rate tests for Ver and Ver-PAM membranes; (a) Water flux of the Ver-PAM membrane; (b) Ka of the Ver-PAM membrane. + and Na + Osmosis flux; (c)H2O 71.90℃ -Ver-PAM membrane K + and Na +Concentration; (d) pH 5.29-Ver-PAM membrane K + and Na + concentration.

[0033] Figure 9 The K-type of the Ions-Ver-PAM membrane is shown. + and Na + Permeation flux.

[0034] Figure 10 The display shows Na+ with different molecular weights of PAM. + -Ver-PAM membrane for K + Na + The effect of permeation flux:

[0035] (a)Na + - Interlayer spacing of Ver-PAM membranes in dry and wet conditions; (b) 150kDa molecular weight PAM; (c) 40kDa molecular weight PAM; (d) 5000-6000kDa molecular weight PAM. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0037] Experimental materials:

[0038] Thermally expanded vermiculite and polyacrylamide (molecular weights of 40 kDa, 150 kDa and 5000-6000 kDa, respectively) were purchased from Sigma-Aldrich (USA).

[0039] Sodium chloride, potassium chloride, lithium chloride, cesium chloride, magnesium chloride, and strontium chloride were all purchased from Aladdin (China).

[0040] The ultrapure water was obtained from the Milli-Q system (Millipore, USA).

[0041] Vermiculite nanosheets are a type of natural mineral material with a layered structure. The single-layer structural unit of a vermiculite nanosheet consists of two layers of silicon-oxygen tetrahedra and one layer of magnesium-oxygen octahedra. The preparation of vermiculite nanosheets typically involves exfoliating natural vermiculite or thermally expanded vermiculite into single-layer or multi-layer two-dimensional nanosheets using chemical or physical methods. These methods include chemical intercalation, liquid-phase exfoliation combined with gradient centrifugation, mechanical exfoliation, spraying, and vacuum filtration.

[0042] The vermiculite nanosheets used in this invention can be prepared by any of the methods described above.

[0043] Molecular self-assembly refers to molecular self-assembly technology, in which molecules spontaneously assemble on a solid surface or at a solid / liquid interface to form a highly ordered ultrathin film.

[0044] This invention provides for K + A method for preparing a selectively transported biomimetic two-dimensional vermiculite film includes the following steps:

[0045] (1) Vermiculite nanosheets were dispersed in a polyacrylamide solution and assembled into a membrane to obtain a Ver-PAM composite membrane.

[0046] The molecular weight of polyacrylamide is 40-6000 kDa;

[0047] The mass ratio of vermiculite nanosheets to polyacrylamide used was 0.3-60:0.1-180;

[0048] (2) Immerse the Ver-PAM composite membrane obtained in step (1) in a cationic solution, wash it, and dry it to obtain the vermiculite membrane.

[0049] Preferably, vermiculite nanosheets are added to a polyacrylamide solution in the form of a solution, that is, the vermiculite monolayer solution is mixed with the polyacrylamide solution and assembled into a film.

[0050] Preferably, the vermiculite monolayer solution is prepared by reacting thermally expanded vermiculite with Na... + Exchange, Li + Obtained by exchange and centrifugation.

[0051] Among them, Na + The exchange process involves placing the thermally expanded vermiculite in a saturated sodium chloride solution, heating and stirring, followed by washing. Specifically...

[0052] Thermally expanded vermiculite was placed in a sodium chloride solution and heated and stirred in an oil bath at 130°C. After the reaction was complete, excess sodium chloride solution was filtered off, and the vermiculite flakes were washed with ultrapure water.

[0053] Li + The exchange process involves placing the cleaned vermiculite flakes in a lithium chloride solution, heating and stirring, and then washing. Specifically...

[0054] The cleaned vermiculite flakes were placed in a lithium chloride solution and heated and stirred in an oil bath at 130°C. After the reaction was complete, the excess lithium chloride solution was filtered off, and the vermiculite flakes were washed with ultrapure water.

[0055] Preferably, the centrifugal separation step is as follows: the vermiculite flakes are washed and filtered with ultrapure water, and after multiple washing and filtrations, the vermiculite nanosheets are dispersed in ultrapure water to obtain a vermiculite monolayer solution.

[0056] The concentration of the vermiculite monolayer solution can be obtained by measurement.

[0057] Preferably, the membrane is formed by filtration, for example, by assembling the membrane using a vacuum-assisted filtration device.

[0058] In step (1), the mass ratio of vermiculite nanosheets to polyacrylamide is 0.3-60:0.1-180. Preferably, the mass ratio is 0.4-55:0.2-170, or 0.5-50:0.3-160, or 0.6-45:0.4-155, or 0.7-44:0.5-150, or 0.8-43:0.8-145, or 0.9-42:0.9-14 0, or 1-41: 1-135, or 2-40: 1.5-130, or 3-39: 2-125, or 4-38: 2.5-120, or 5-37: 3-115, or 6-36: 3.5-110, or 7-35: 4-105, or 8-34: 4.5-100, or 9-33: 5-95, or 10-32: 5.5-90, or 15-31: 6-80.

[0059] More preferably, the mass ratio of vermiculite nanosheets to polyacrylamide is 1:0.1-10, or 1:0.1-9, or 1:0.1-8, or 1:0.1-7, or 1:0.1-6, or 1:0.1-5, or 1:0.2-5, or 1:0.2-4.5, or 1:0.2-4, or 1:0.2-3.

[0060] In the actual preparation process of Ver-PAM composite membrane, the mass ratio of vermiculite nanosheets to polyacrylamide can be any specific ratio within the above-mentioned mass range. For example, the mass ratio of vermiculite nanosheets to polyacrylamide can be 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.5, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, or 1:5, etc., which will not be elaborated here.

[0061] During the preparation of the Ver-PAM composite membrane, the mass of vermiculite nanosheets and polyacrylamide varied within the above-mentioned large range, but the performance of the final Ver-PAM composite membrane did not change significantly. In the prepared Ver-PAM composite membrane, the range of PAM and vermiculite nanosheets was 0-165% (mass percentage).

[0062] In step (1), the molecular weight of the polyacrylamide is 40-6000 kDa. Preferably, the molecular weight of the polyacrylamide is 40 kDa, 150 kDa, or 5000-6000 kDa, or other molecular weights of polyacrylamide available commercially.

[0063] Because polyacrylamide is a low-entropy polymer, on the one hand, polyacrylamide with a relatively large molecular weight is easier to load onto vermiculite nanosheets; on the other hand, the continuous arrangement of carbonyl functional groups in polyacrylamide with a relatively large molecular weight is beneficial for K... + Rapid transport between monolayers of vermiculite nanosheets, when the molecular weight of polyacrylamide is 5000-6000 kDa, K + The osmosis rate can reach 297 mmol m -2 h -1 .

[0064] In step (2), the Ver-PAM composite membrane is immersed in a cationic solution, washed with water, and dried to obtain the vermiculite membrane.

[0065] Preferably, the immersion time of the Ver-PAM composite membrane in the cationic solution is based on the requirement that ions can fully penetrate into the interlayer of the composite membrane. Those skilled in the art can make a judgment based on the actual situation. For example, the immersion time of the Ver-PAM composite membrane is 1h, 2h, 3h, 4h, 6h, 12h, 24h, 36 hours or 48 hours, etc.

[0066] Preferably, the cation solution is selected from monovalent metal ion solutions, including lithium ion solutions, sodium ion solutions, potassium ion solutions, or cesium ion solutions; wherein, the lithium ion solution can be prepared from lithium chloride, lithium hydroxide, lithium sulfate, lithium carbonate, lithium nitrate, lithium phosphate, lithium bromide, or lithium iodide, etc.

[0067] Sodium ion solutions can be prepared from sodium salts such as sodium chloride, sodium hydroxide, sodium chloride, sodium carbonate, sodium sulfate, sodium bicarbonate, sodium nitrate, sodium bromide, or sodium iodide.

[0068] Potassium ion solutions can be prepared from potassium salts such as potassium chloride, potassium hydroxide, potassium sulfate, potassium carbonate, potassium nitrate, potassium bromide, or potassium iodide.

[0069] Cesium ion solutions can be prepared from cesium chloride, cesium fluoride, cesium sulfate, cesium carbonate, or cesium hydroxide, etc.

[0070] This invention introduces cations into the interlayer space of Ver-PAM membranes. Because vermiculite monolayers are negatively charged, they form strong electrostatic interactions with metal ions, which helps maintain a stable interlayer space and avoids the swelling behavior of Ver-PAM membranes in aqueous solutions, effectively controlling the interlayer spacing. Simultaneously, cations adsorb and embed themselves in the hexaoxane vacancies composed of silicon-oxygen tetrahedra on the vermiculite monolayers, forming inner-sphere complexes, further controlling the interlayer spacing. Furthermore, the ability of cations to form inner-sphere complexes with the hexaoxane vacancies on the vermiculite monolayers decreases with increasing hydration radius (hydration radius: Cs). + <K + <Na + <Li + Divalent ions (Mg) 2+ 、Sr 2+ Compared to monovalent cations, divalent ions have a larger hydration radius and cannot trap in hexaoxygen vacancies to form inner-sphere complexes. Therefore, the interlayer space of Ver-PAM membranes soaked with divalent ions is extremely large.

[0071] Preferably, the concentration of the cation solution is 0.1-10 mol / L, or 0.2-9 mol / L, 0.3-8 mol / L, 0.4-7 mol / L, 0.5-6 mol / L, 0.5-5 mol / L, 0.5-4 mol / L, 0.5-3 mol / L, 0.2-2 mol / L, 0.5-1.5 mol / L, 0.5-1.4 mol / L, 0.5-1.3 mol / L, 0.5-1.2 mol / L, 0.5-1.1 mol / L, 0.5-1 mol / L, or any value within the above range, such as 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 0.1 mol / L, 1.2 mol / L, etc.

[0072] When the concentration of the cation solution is low, the rate at which cations enter the interlayer is slow, while when the concentration of cations is high, the rate at which cations enter the interlayer is fast. In order to maintain the consistency of the interlayer distance and avoid the differences caused by the cation concentration, the Ver-PAM composite membrane can be immersed in the cation solution for a relatively long time.

[0073] Example 1: Preparation of vermiculite monolayers

[0074] (1) Na + exchange

[0075] 300-600 mg of thermally expanded vermiculite and 300 mL of saturated sodium chloride solution were placed separately in 500 mL round-bottom flasks and heated and stirred in an oil bath at 130 °C for 24 h, with a 25 °C water bath used as the circulating cooling water. After the reaction was completed, excess sodium chloride solution was filtered out while hot using a vacuum filter, and the vermiculite flakes were washed with ultrapure water.

[0076] (2)Li + exchange

[0077] The cleaned vermiculite flakes were mixed with 300 mL of 2 mol L... -1 Lithium chloride solution was placed in 500 mL round-bottom flasks and heated and stirred in an oil bath at 130 °C for 24 h, with a 25 °C water bath used as circulating cooling water. After the reaction was completed, excess lithium chloride solution was filtered out while hot using a vacuum filtration device, and vermiculite flakes were washed with ultrapure water.

[0078] (3) Centrifugal separation

[0079] The cleaned vermiculite flakes were dispersed in ultrapure water and centrifuged at 10,000 rpm until the conductivity of the supernatant was below 2 μS / cm. -1 .

[0080] The vermiculite precipitate in the centrifuge tube was dispersed in ultrapure water, centrifuged at 3000 rpm for 10 min, and the supernatant was collected. The precipitate was then dispersed in ultrapure water again and sonicated at 100 Hz for 10 min. After sonication, the mixture was centrifuged at 3000 rpm for 10 min, and the supernatant was collected.

[0081] The collected supernatant was centrifuged at 3000 rpm until no precipitate was found at the bottom of the centrifuge tube. At this point, the supernatant was a vermiculite monolayer solution.

[0082] After centrifuging the supernatant at 12,000 rpm for 10 minutes, collect the precipitate at the bottom of the centrifuge tube and disperse it in ultrapure water to obtain a vermiculite monolayer solution.

[0083] (4) Concentration determination

[0084] The concentration of the vermiculite monolayer solution was determined using the differential method. A blank silicon wafer was weighed using an electronic analytical balance and recorded as m1. Then, 1 mL of the vermiculite monolayer solution prepared above was added dropwise to the blank silicon wafer, and it was placed on a 100°C drying rack to dry. After drying, it was cooled to room temperature and the silicon wafer was weighed again using an electronic analytical balance and recorded as m2. The concentration of the vermiculite monolayer can be calculated using Formula 1:

[0085]

[0086] Wherein, c(mg mL) -1 m1(mg) is the concentration of the vermiculite monolayer solution; m2(mg) is the total mass of the silicon wafer and the vermiculite monolayer; m1(mg) is the mass of the blank silicon wafer; V(mL) is the volume of the vermiculite monolayer solution added to the silicon wafer.

[0087] Example 2: Preparation of blank vermiculite film (Ver)

[0088] After the concentration of the vermiculite monolayer solution was determined, a vermiculite monolayer solution containing 6 mg of vermiculite monolayer was added to 100 mL of ultrapure water. A blank vermiculite membrane with a thickness of 2 μm was prepared by vacuum filtration using a PES membrane with a pore size of 220 nm and a diameter of 47 nm as the substrate membrane.

[0089] Example 3: Preparation of Vermiculite-Polyacrylamide Membrane (Ver-PAM)

[0090] PAM was dispersed in deionized water to obtain a PAM solution, and its concentration was maintained at 1 mg / mL. -1 Store in a cool, dark place.

[0091] A solution containing 6 mg of vermiculite nanosheets was mixed with 1.2 mL, 3 mL, 6 mL, and 18 mL of PAM solution for 5 min, respectively, and then assembled into membranes using a vacuum-assisted filtration device. The membranes were named Ver-PAMX%, where X% represents the mass percentage of PAM in the Ver-PAM solution measured by thermogravimetric analysis. The Ver-PAM membranes were then treated under vacuum at 60 °C for 4 h. Finally, a Ver-PAM composite membrane with confined channels was obtained.

[0092] The preparation process of Ver-PAM membrane is as follows: Figure 1 As shown.

[0093] The thickness and size distribution of the vermiculite monolayer in Example 2 were examined using atomic force microscopy (AFM, BRUKER, Germany).

[0094] like Figure 2 As shown in the atomic force microscope (AFM) images, the vermiculite nanosheets exhibit an ultrathin thickness of approximately 1.20 nm (due to the presence of some water molecules on the surface of the vermiculite nanosheets, the measured thickness of the vermiculite nanosheets is greater than the theoretical thickness of 0.83 nm). The size distribution of the vermiculite nanosheets is 2-3 μm, which is beneficial for constructing uniform and ordered layered channels.

[0095] The Ver-PAM film in its dry state was characterized using a scanning electron microscope (SEM, TM3030, Hitachi, Japan). The interlayer spacing of the Ver and Ver-PAM films in both dry and wet states was analyzed using X-ray diffraction (XRD, Empyrean). The infrared spectra of Ver, PAM, and Ver-PAM were obtained using Fourier transform infrared spectroscopy (FT-IR, Nicolet iS50, USA).

[0096] like Figure 3 As shown, the energy dispersive X-ray spectroscopy (EDX) results of the Ver-PAM film surface show that C and N elements are uniformly distributed in the Ver-PAM film, indicating that the PAM polymer is uniformly distributed between the vermiculite monolayers.

[0097] From Fourier Transform Infrared (FTIR) spectroscopy ( Figure 4 2930cm can be observed in ) -1 The nearby peak, which corresponds to the stretching vibration peak of the methylene group in the PAM framework, is located at 1651 cm⁻¹. -1 The nearby peaks represent the C=O stretching vibrations of the amide groups in the PAM framework, proving that PAM was successfully introduced into the interlayer of vermiculite monolayers.

[0098] Meanwhile, the interlayer spacing of the Ver membrane is Under humid conditions, the interlayer spacing of the Ver membrane is Because the PAM polymer in the Ver-PAM film exists in a coiled form between the layers, two types of interlayer spacing occur. Specifically, Ver-PAM... 33.93％ The interlayer spacing of the membranes are respectively and Under humid conditions, the Ver-PAM membrane exhibits swelling behavior, and its Bragg peak almost disappears, as shown in the XRD results. Figure 5 As shown, the Ver-PAM membrane exhibits swelling behavior in aqueous solution, making it difficult to maintain a stable interlayer spacing.

[0099] Example 4: Preparation of vermiculite-polyacrylamide membranes (Ions-Ver-PAM) with different interlayer cations

[0100] The Ver-PAM composite membrane (Ver-PAM) prepared in Example 3 was used. 5.82％ Ver-PAM 11.54％ Ver-PAM 33.93％ and Ver-PAM 50.03％ Soak in 1 mol L of water respectively -1Ions-Ver-PAM membranes were obtained by immersing the membranes in solutions of lithium chloride, sodium chloride, potassium chloride, cesium chloride, magnesium chloride, and strontium chloride for 24 hours to ensure that the cations could fully penetrate into the interlayer of the Ver-PAM composite membrane. + -Ver-PAM membrane, Na + -Ver-PAM membrane, K + -Ver-PAM membrane, Cs + -Ver-PAM membrane, Mg 2+ -Ver-PAM membrane, Sr 2+ -Ver-PAM membrane.

[0101] After cleaning the surface of these composite membranes with ultrapure water to remove ions, they were placed in an oven at 60°C and vacuum dried for 4 hours.

[0102] The interlayer spacing of the ions-Ver-PAM film under dry and wet conditions was analyzed by X-ray diffraction (XRD, Empyrean).

[0103] Ver-PAM 5.82％ Ver-PAM 11.54％ Ver-PAM 33.93％ and Ver-PAM 50.03％ Immersed in 1 mol / L Li + Na + K + Cs + Mg 2+ and Sr 2+ After 24 hours in the solution, the membranes were washed and dried in a 60℃ oven for 4 hours, and their XRD patterns were measured in the dry state. XRD data for the wet state were obtained by immersing the dried membranes in pure water for 24 hours. Results are as follows: Figure 6 As shown in the image. Compared to Ver-PAM (including Ver-PAM) soaked in pure water. 5.82％ Ver-PAM 11.54％ Ver-PAM 33.93％ and Ver-PAM 50.03％ The interlayer spacing of the Li film changed significantly after an ionic solution was introduced into the interlayer. + -Ver-PAM, Na + -Ver-PAM, K + -Ver-PAM, Cs + -Ver-PAM, Mg 2+ -Ver-PAM and Sr 2+ The interlayer spacing of -Ver-PAM films, from narrowest to widest, is Cs + <K +<Na + <Li + <Sr 2+ ≈Mg 2+ On the one hand, due to the negative charge of vermiculite monolayers, a strong electrostatic interaction is formed with metal ions, maintaining a stable interlayer space in the ions-Ver-PAM film in aqueous solution. On the other hand, Cs + -Cs between Ver-PAM membrane layers + Adsorbed and trapped within the hexaoxane cavities composed of silicon-oxygen tetrahedra on vermiculite monolayers, they form inner-sphere complexes. The ability of monovalent ions to form inner-sphere complexes with hexaoxane cavities on vermiculite monolayers decreases with increasing hydration radius (hydration radius: Cs). + <K + <Na + <Li + Divalent ions (Mg) 2+ 、Sr 2+ Due to its excessively large hydration radius, it cannot embed itself within hexaoxygen cavities to form inner-sphere complexes. Therefore, the interlayer space of the divalent ion Ver-PAM membrane is extremely large after immersion.

[0104] from Figure 7 The XRD pattern of a showed that as the Ver-PAM film was applied to Na... + As the immersion time in the solution increases, the Bragg peak changes from a bimodal to a single peak. Due to van der Waals forces and hydrogen bonds between non-bonded atoms, groups, and molecules in the PAM polymer, it often exists in a coiled form between vermiculite monolayers. However, high concentrations of ionic solution compete with the polymer for water molecules, causing the hydrogen bonds between water molecules and polymer chains to break (salting out). Simultaneously, H and O in the ion-hydrated layer can also form hydrogen bonds with H, O, and N in the polymer, further weakening the hydrogen bonding. Therefore, the PAM between vermiculite layers changes from a coiled state to a stretched state.

[0105] like Figure 7 As shown in bc, the conformation of the vermiculite monolayer interlayer polymer can also be changed in many ways, such as by immersing it in an aqueous solution, increasing the temperature, or changing its pH value.

[0106] Example 5 Performance Test

[0107] The water vapor permeation rates of the Ver membrane and Ver-PAM membrane were measured using a water vapor diffusion device. Figure 8 As shown in Figure a, because the PAM polymer blocks the interlayer space, the path for water to pass through becomes longer, and the water vapor permeation rate decreases with the increase of PAM content.

[0108] Na+ in Ver and Ver-PAM membranes was measured using an ion diffusion apparatus. + K + Permeation rate, such as Figure 8 As shown in b, Na + and K + The permeation rate increases with the addition of AM polymer. This phenomenon is due to the strong affinity between ions and the carbonyl functional groups on the PAM polymer between vermiculite monolayers. Driven by the ion concentration gradient, ions are transported by jumping along the polymer chains. However, the swelling behavior of the Ver-PAM membrane under humid conditions causes it to lose angstrom-sized interlayer channels, and Na... + K + All can pass quickly (among which, Ver-PAM) 33.93％ Membrane transport K + The permeation rate is only higher than that of Na + (Approximately 3 times faster).

[0109] In addition, Ver-PAM was altered by increasing the temperature and adjusting the pH of the aqueous solution. 33.93％ The conformation of the PAM polymer in the membrane and the measurement of Na were performed separately. + K + Permeation rate, such as Figure 8 As shown in cd. Due to the lack of suppression of Ver-PAM. 33.93％ Swelling behavior of membranes under humid conditions, Na + K + The permeation rates did not show a significant difference.

[0110] Select ions-Ver-PAM 33.93％ The membrane serves as a research model and is used to measure Na. + K + Diffusion rate. ions-Ver-PAM 33.93％ Equal amounts of salt solution (feed side) and ultrapure water (pure water side) were added to the left and right sides of the membrane, respectively. After diffusion for 24 hours, the ion concentration on the pure water side was measured, and the ion permeation rate could be calculated using Formula 2.

[0111]

[0112] Wherein, P(mol m -2 h -1 ) represents the ion permeation rate; V (mL) represents the volume of the pure water solution; c (mg / L) represents the volume of the pure water solution. -1 A(m) represents the ion concentration on the pure water side; 2 ) represents the effective diffusion area of ​​the membrane; t(h) represents the diffusion time.

[0113] like Figure 9 As shown, Na +-Ver-PAM 33.93％ The membrane significantly improved K + The permeation rate is higher than that of Na + It's about 9 times faster, while other membranes didn't show significant differences. Na + K + Entering the narrow passageway between floors, K + -Ver-PAM 33.93％ Cs + -Ver-PAM 33.93％ The membrane needs to overcome a higher dehydration energy barrier, which significantly hinders the dehydration of Na+. + K + The operation of Mg. 2+ -Ver-PAM 33.93％ 、Sr 2+ -Ver-PAM 33.93％ The interlayer channels of the membrane lost their angstrom size, causing Na... + K + The permeation rates are all very high. Li + Li has a higher hydration energy than other monovalent ions, making it more likely to combine with water. + Carrying a large number of water molecules into the interlayer causes Li + -Ver-PAM 33.93％ The interlayer structure of the membrane is unstable. Therefore, it possesses a certain interlayer space. Furthermore, structurally stable membranes have potential applications in the field of ion separation.

[0114] Choose Na + -Vermiculite membranes with PAM content increasing from 0 to 50.03% by mass (concentration gradients of 0%, 5.82%, 11.54%, 33.93%, and 50.03%) were used, and Na was measured. + K + Diffusion rate.

[0115] like Figure 10 As shown in a, Na + The interlayer channels of the Ver-PAM membrane no longer narrow.

[0116] like Figure 10 As shown in b, with the increase of PAM content, K + The diffusion rate increased from 34.33 mmol / m³. -2 h -1 Increased to 101.32 mmol m -2 h -1 This further improved K + The permeation rate, relatively speaking, at a PAM concentration of 5.82%, Na + The diffusion rate was 7.19 mmol m-2 h -1 Furthermore, at PAM concentrations of 5.82-33.93%, Na + The diffusion rate did not change significantly, but as the PAM content increased to 50.03%, Na... + The diffusion rate increased to 30.90 mmol m -2 h -1 .

[0117] It is evident that, in addition to inhibiting interlayer swelling of vermiculite monolayers and regulating channel size, PAM concentration also mediates K... + It plays an important role in transmission. + Hydration energy is greater than K + Na + A higher dehydration energy barrier needs to be overcome to enter the narrow interlayer. Simultaneously, it interacts with hydrated Na... + In comparison, hydrated K + The hydration diameter is smaller when entering the sub-nanometer channel, resulting in stronger dehydration capacity. Partially dehydrated K... + Entering the interlayer, the carbonyl oxygen in the interlayer reacts with K + Coordination, to compensate for the energy loss caused by dehydration, is driven by external concentrations, K + Transported by skipping along the polymer chain (similar to the KcsA channel).

[0118] In addition to the 150 kDa PAM used in the above experiments, PAMs with molecular weights of 40 kDa and 5000-6000 kDa were also selected. The different molecular weights of PAM were introduced into vermiculite monolayers according to the methods described in the examples, and the effects of Na were investigated. + K + Diffusion rate.

[0119] like Figure 10 As shown in cd, Na + -Ver-PAM 27.57％ (40kDa) and Na + -Ver-PAM 11.42％ (5000-6000kDa) K + The permeation rate is respectively higher than that of Na + The values ​​are 4 times and 16 times higher. Due to the low entropy of PAM polymers, 5000-6000 kDa PAM is more easily loaded onto vermiculite monolayers than 40 kDa and 150 kDa PAM. Meanwhile, the continuous arrangement of carbonyl functional groups makes K... + Interlayer transport is extremely fast, reaching 297 mmol / m². -2 h -1 .

[0120] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for K + manufacturing a biomimetic two-dimensional mica film for specific transmission, characterized by, The preparation method comprises the following steps: (1) adding vermiculite nanosheets in the form of a solution into a polyacrylamide solution, assembling into a film, and obtaining a Ver-PAM composite film; the mass ratio of vermiculite nanosheets to polyacrylamide is 0.3-60:0.1-180; the molecular weight of polyacrylamide is 40 kDa-6000 kDa; (2) soaking the Ver-PAM composite film obtained in step (1) in a cation solution, washing, and drying, to obtain the vermiculite film; the cation solution comprises a lithium ion solution, a sodium ion solution, or a strontium ion solution, and the concentration of the cation solution is 0.01-10 mol / L.

2. The production method according to claim 1, characterized by, In step (1), the vermiculite nanosheets are dispersed in the polyacrylamide solution, assembled into a film through vacuum filtration, dried, and then the Ver-PAM composite film is obtained.

3. The preparation method according to claim 2, characterized in that, In step (2), the Ver-PAM composite film obtained in step (1) is soaked in a cation solution, the cations are fully introduced into the interlayer of the Ver-PAM composite film, washed with ultrapure water, and then dried.

4. The biomimetic two-dimensional vermiculite film for K+ specific transport obtained by the preparation method of any one of claims 1-3.

5. A method for efficient separation of Na + , K + , characterized in that, The method comprises the step of separating a sample to be treated using the vermiculite film obtained by the preparation method of any one of claims 1-3, or using the vermiculite film of claim 4.

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