Niobate / graphene oxide composite two-dimensional film and application thereof

Abstract

The invention discloses a niobate two-dimensional membrane, a niobate / graphene oxide composite two-dimensional membrane and application thereof, and belongs to the technical field of membrane separation or alkali metal separation. The niobate two-dimensional membrane is used for intercepting Na < + > in alkali metal ions, the niobate / graphene oxide composite two-dimensional membrane is used for realizing preferential passing of Li < + > in the alkali metal ions, the niobate two-dimensional membrane and the niobate / graphene oxide composite two-dimensional membrane are further connected in series, and separation and enrichment of lithium ions are realized in a Na < + > / K < + > / Li < + > system. And a road is developed for sustainable acquisition of strategic metal ion resources.

Description

Technical Field

[0001] This invention belongs to the field of alkali metal ion separation technology, and more specifically, relates to a niobate nanosheet, a niobate two-dimensional membrane and their application in alkali metal ion separation, a niobate / graphene oxide composite nanosheet, a niobate / graphene oxide composite two-dimensional membrane and a two-dimensional membrane combination device and their application in alkali metal ion separation. Background Technology

[0002] Alkali metal ion separation has significant theoretical and practical value. Especially against the backdrop of surging demand for lithium resources driven by sustainable energy development, a deep understanding of the selective ion transport mechanism in nano-confined channels is crucial for advancing applications such as chemical separation and energy storage. Among these, accurately distinguishing monovalent cations (such as Li) is particularly important. + Na + K + Alkali metal ion separation has become a core challenge in ensuring the sustainable supply of critical strategic metals. Previous research has primarily focused on designing separation membranes containing nanochannels, utilizing size sieving effects, Donnan repulsion, or dehydration mechanisms to achieve alkali metal ion separation. However, because alkali metal ions share similar charges and valence states, and their hydrated ionic radii differ very little (approximately 24-51 pm, on the sub-angstrom scale), approaching the thermal fluctuation range of typical ion channel (e.g., KcsA) pore sizes (approximately 50-80 pm), existing separation methods based on nanochannel-sized membranes struggle to effectively distinguish these highly similar ions. Currently, the selectivity of state-of-the-art alkali metal ion separation membranes is generally below 10, highlighting the significant limitations of existing size-based separation strategies in addressing this challenge.

[0003] A prior art technique published in Nature Communications (Nature Communications, 2025, 16, 4626) discloses a molecularly engineered large-area nanoporous single-atom-thickness graphene alkali metal ion separation membrane. The membrane is constructed using porous graphene material to create a MAP-PNG membrane, and Li is separated by controlling the nanopore size distribution, i.e., the nanochannel size. + Na + K + The separation ratio of the two-component K+ / Li+ is 20.8. Its advantages lie in the uniform size of the nanochannels, which improves the separation selectivity while ensuring good mechanical stability and has the potential for extended synthesis. However, its shortcomings are the low ion flux and the difficulty in uniformly coating the polymer during the preparation process, and the separation selectivity still needs to be further improved.

[0004] Prior art published in Science Advances (Science Advances, 2024, 10, eado3998) discloses a conductive MXene alkali metal ion separation membrane with polydopamine-confined angstrom-level channels. The MXene-PDA membrane is constructed using two-dimensional transition metal carbide (MXene) materials. By controlling the membrane channel voltage gating and ion charge, Li is separated primarily through Donnan repulsion. + Na + K + Specifically, Na + / K + The separation ratio was 4.8 (single component), K + / Na + The separation ratio was 3.3 (single component); K + / Li + The separation ratio was 40.9 (two-component), Na + / Li + For 7.1 (two-component), K + / Na + The value is 3.0 (two-component), which has the advantage of being suitable for K. + The high on / off ratio of the transmission exhibits beneficial selectivity and voltage controllability, but its selectivity depends on the exogenous cation Mg. 2+ The concentration of the ions and too many other factors, such as ionic strength, were not studied in greater depth in more practical multi-component systems.

[0005] Based on the foregoing, although many separation membranes for separating alkali metal ions have been reported in the prior art, due to the fact that alkali metal ions (especially Li) are still relatively rare, the separation membranes are not widely used. + Na + K + The two-dimensional separation membrane materials with high separation ratio for separating alkali metal ions have been found in the existing technology because they are highly similar in size and physicochemical properties. Summary of the Invention

[0006] In the prior art, niobates are mainly used in the field of photodegradable dye technology. This invention is the first to prepare them into monodisperse niobate nanosheets that are mainly single-layered, and then prepare them into two-dimensional films. This invention is the first to discover that the special "human" shaped channel and "zigzag" shaped channel structure formed by them can be applied to the separation of alkali metal ions.

[0007] To construct a two-dimensional membrane with excellent separation function for alkali metal ions, monodisperse niobate nanosheets should first be prepared. This invention is the first to prepare monodisperse niobate nanosheets in a predominantly monolayer form. Based on this: The first objective of this invention is to provide a highly efficient method for separating Na.+ With K + and / or Li + Two-dimensional membranes and nanosheet raw materials for preparing the membrane material.

[0008] The second objective of this invention is to provide a highly efficient method for separating K. + With Li + Two-dimensional membranes and nanosheet raw materials for preparing the membranes.

[0009] A third objective of this invention is to provide a two-dimensional membrane assembly device that, through the combination of two-dimensional separation membranes as described in the first and second objectives of this invention, can separate Na... + K + and Li + Efficient separation of Li in ternary systems + .

[0010] 1. Niobate nanosheets A first aspect of the present invention provides a niobate nanosheet, wherein more than 80% of the niobate nanosheet has a thickness of less than 5 nm and a maximum lateral dimension of 100 nm or more.

[0011] Since the thickness of a single-layer niobate nanosheet is about 2 nm, and niobate nanosheets with a thickness of less than 5 nm are single-layer or double-layer niobate nanosheets, niobate nanosheets with the above-mentioned thickness and maximum lateral size characteristics are ideal materials for preparing the two-dimensional membrane with separation properties of the present invention.

[0012] It should be noted that the 80% mentioned here refers to the number of niobate nanosheets. Typically, when observing steps thicker than 1 nm in atomic force microscopy (AFM), the number of niobate nanosheets in the observed area should be no less than 20. When preparing the sample for AFM observation, the niobate nanosheets are dispersed in a volatile solvent (concentration approximately 0.3 mg / mL). A drop is placed onto the support, and after the solvent evaporates, AFM testing is performed to observe the sample's thickness and size. The niobate referred to in this article refers to M... x H y Nb6O 17 Wherein, M is selected from K, Na, or Li; x + y = 4, 2 ≤ x < 4, 0 < y ≤ 2. Preferably, M is potassium (K). Niobium in niobates is pentavalent, for example, K₂H₂Nb₆O. 17 K 2.5 H 1.5 Nb6O 17 K3H1Nb6O 17 , or K 3.5 H 0.5 Nb6O 17The x and y values ​​can be detected and calculated using EDS (Electronic Data Separation).

[0013] The thickness of a single-layer niobate nanosheet is approximately 2 nm. Therefore, when AFM detects a thickness of less than 5 nm for niobate nanosheets, the number of layers typically does not exceed two. Niobate nanosheets with no more than two layers, compared to multilayer (≥3 layers) niobate nanosheets, are more likely to form herringbone channels when constructing two-dimensional films, exhibiting superior Ki properties. + Li + Exchange capacity. However, in microstructures, unlike macrostructures, it is not possible for 100% of the nanosheets to achieve the target thickness and size. Only a majority of the nanosheets need to meet this condition to achieve the invention's objective. Therefore, the first aspect of this invention specifies that the proportion of niobate nanosheets meeting this requirement is above 80%. Niobate nanosheets meeting this requirement can be used to prepare two-dimensional membranes with excellent separation capabilities.

[0014] According to a preferred embodiment of any technical solution of the first aspect of the present invention, more than 80% of the niobate nanosheets have a thickness of less than 3 nm and the maximum lateral dimension of the niobate nanosheets is greater than or equal to 100 nm.

[0015] When AFM detects a thickness of less than 3 nm for niobate nanosheets, the niobate nanosheets typically consist of a single layer. Single-layer niobate nanosheets, compared to those with two or more layers, are more likely to form herringbone channels when constructing two-dimensional films, exhibiting superior K0 properties. + Li + Exchange capacity.

[0016] Preferably, the maximum lateral dimension of the niobate nanosheets is 0.1~10 μm, more preferably 1~7 μm, and most preferably 2~6 μm. Large-sized two-dimensional materials exhibit better long-range order when constructing two-dimensional films.

[0017] According to a preferred embodiment of any technical solution of the first aspect of the present invention, the niobate nanosheets contain 56.55% to 61.28% niobium by mass, excluding 56.55%. The niobate nanosheets shall be calculated on a dry weight basis, and the content of the metallic element niobium shall be determined by XPS method.

[0018] According to a preferred embodiment of any technical solution of the first aspect of the present invention, the niobate nanosheets are potassium niobate nanosheets, and the mass percentage of potassium in the niobate nanosheets is 8.60%~15.86%, excluding 15.86%. The niobate nanosheets shall be calculated on a dry weight basis, and the content of the metallic element potassium shall be determined by XPS method.

[0019] 2. Dispersion of niobate nanosheets A second aspect of the present invention provides a dispersion containing niobate nanosheets as described in any of the technical solutions of the first aspect of the present invention, wherein the dispersion medium of the dispersion contains water.

[0020] According to a preferred embodiment of any technical solution of the second aspect of the present invention, the mass concentration of the dispersed phase in the dispersion is 0.01~100 mg / mL, preferably 0.1~10 mg / mL, more preferably 0.1~5 mg / mL, and most preferably 0.1~1 mg / mL. When the mass concentration of the dispersed phase is too high, the dispersed phase is prone to agglomeration.

[0021] 【3. Preparation methods of niobate nanosheets or dispersions】 The third invention provides a method for preparing a dispersion of niobate nanosheets as described in any of the first aspects of the invention, or a dispersion of niobate nanosheets as described in any of the second aspects of the invention, comprising the following steps: Soaking steps: Add M4Nb6O 17 The crystals are immersed in an acidic solution to obtain an acidic dispersion; M is selected from K, Na, or Li; preferably, M is K; wherein, K4Nb6O 17 Crystals can be obtained using existing preparation methods; Intercalation step: The acidic dispersion is subjected to hydrothermal intercalation to obtain an intercalated dispersion; the hydrogen in the acidic solution is exchanged to remove K4Nb6O. 17 The crystal contains a portion of potassium ions; preferably, the portion of potassium ions is no more than half of the total potassium ions. Microfluidization step: The intercalated dispersion is microfluidized using a microfluidic jet injector to obtain a microfluidized dispersion; Centrifugation step: The microfluidic dispersion is centrifuged to obtain a dispersion of niobate nanosheets; if niobate nanosheets are required, they can be separated from the dispersion and dried. Drying methods can include, for example, freeze-drying, spray drying, vacuum drying, or room temperature evaporation.

[0022] According to a preferred embodiment of any technical solution of the third aspect of the present invention, in the microfluidization step, the pressure of the microfluidic ejector is 500~2000 bar, and the microfluidization treatment time is 0.5~10 h. Within this pressure and treatment time range, more monolayer niobate nanosheets can be obtained. Preferably, the pressure of the microfluidic ejector is 800~1600 bar, and the microfluidization treatment time is 1~8 h. More preferably, the pressure of the microfluidic ejector is 1000~1400 bar, and the microfluidization treatment time is 2~6 h.

[0023] According to a preferred embodiment of any technical solution of the third aspect of the present invention, in the centrifugation step, the centrifugation speed is 500~10000 rpm. Controlling the centrifugation speed within this range allows nanosheets with a layer thickness greater than two layers to precipitate, resulting in a low proportion of nanosheets with a thickness greater than two layers in the resulting upper liquid, which is beneficial for obtaining single-layer or double-layer niobate nanosheets. Preferably, the centrifugation speed is 600~2000 rpm. More preferably, the centrifugation speed is 700~1500 rpm.

[0024] According to a preferred embodiment of any technical solution of the third aspect of the present invention, in the soaking step, the acidic solution is a hydrochloric acid solution, and the soaking time is 48~96 h.

[0025] According to a preferred embodiment of any technical solution of the third aspect of the present invention, in the intercalation step, the hydrothermal intercalation temperature is 120±5 ℃ and the reaction time is 48~96 h.

[0026] 4. Niobate two-dimensional membranes This invention is the first to discover, using ACTEM, the presence of "V"-shaped and "Z"-shaped channels between the layers of niobate two-dimensional films. The regular "V"-shaped channels allow preferential passage of lithium or potassium ions with low resistance, while the regular "Z"-shaped channels allow preferential passage of lithium ions but with higher resistance. Both types of channels affect Na+. + All exhibited specific inhibitory effects, making them effective in Li + and / or K + with Na + When coexisting, the niobate two-dimensional film can achieve the protection of Na+. + The interception.

[0027] Based on this, a fourth aspect of the present invention provides a two-dimensional niobate membrane, wherein the two-dimensional niobate membrane comprises niobate nanosheets; The composition of the niobate nanosheets is M x H y Nb6O 17 Where M is selected from K, Na or Li; x+y=4, 2≤x<4, 0<y≤2; In the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 5 nm and a maximum lateral dimension of greater than or equal to 100 nm; preferably, the maximum lateral dimension of the niobate nanosheets is 0.1~10 μm, more preferably 1~7 μm, and most preferably 2~6 μm. Large-size two-dimensional materials exhibit better long-range order when constructing two-dimensional films. The thickness of the niobate two-dimensional film is 0.05~10 μm, preferably 0.1~9 μm, and more preferably 0.5~6 μm; Herman orientation factor of the niobate two-dimensional film f Not less than 0.9.

[0028] Under certain preferred conditions, in K + / Na + In the binary system, niobate two-dimensional films exhibit the highest 45.8 (K) + / Na + The separation factor of ) and in Li + / Na + In the binary system, niobate two-dimensional films exhibit the highest performance at 33.1 (Li + / Na + The separation factor is much higher than that reported in the prior art.

[0029] It should be noted that this invention has discovered that when the Herman orientation factor of a niobate two-dimensional film... f At lower temperatures, the interlayer "V"-shaped channels in the two-dimensional film are larger and more irregular, resulting in insufficient retention of sodium ions by the prepared niobate two-dimensional film, for example, the orientation factor... f When K is 0.82, the single-component K + / Na + and Li + / Na + The separation ratios were only 1.7 and 3.3, respectively.

[0030] It is worth noting that, due to the greater resistance of the zigzag channel, when both the zigzag and human-shaped channels are unobstructed, ions preferentially pass through the human-shaped channel.

[0031] According to a preferred embodiment of any of the fourth aspects of the present invention, the Herman orientation factor of the niobate two-dimensional film... f Not less than 0.92, more preferably not less than 0.95, and most preferably not less than 0.97.

[0032] According to a preferred embodiment of any technical solution of the fourth aspect of the present invention, more than 80% of the niobate nanosheets have a thickness of less than 3 nm and a maximum lateral dimension of niobate nanosheets greater than or equal to 100 nm. As mentioned above, niobate nanosheets with a thickness of less than 3 nm are almost entirely monolayers, and when prepared into two-dimensional films, they exhibit more ideal separation performance.

[0033] Preferably, the maximum lateral dimension of the niobate nanosheets is 0.1~10 μm, more preferably 1~7 μm, and most preferably 2~6 μm. Large-sized two-dimensional materials exhibit better long-range order when constructing two-dimensional films.

[0034] According to a preferred embodiment of any technical solution of the fourth aspect of the present invention, the niobate nanosheets are potassium niobate nanosheets, and the potassium niobate nanosheets have a composition of K. x H y Nb6O 17 , where x+y=4, 2≤x<4, 0<y≤2.

[0035] According to a preferred embodiment of any technical solution of the fourth aspect of the present invention, the niobate two-dimensional membrane contains 56.55% to 61.28% niobium by mass, excluding 56.55%. The niobate two-dimensional membrane shall be calculated on a dry weight basis, and the content of the metallic element niobium shall be determined by XPS method.

[0036] According to a preferred embodiment of any technical solution of the fourth aspect of the present invention, the niobate nanosheets are potassium niobate nanosheets, and the mass percentage of potassium in the niobate two-dimensional membrane is 8.60%~15.86%, excluding 15.86%. The niobate two-dimensional membrane shall be calculated on a dry weight basis, and the content of the metallic element potassium shall be determined by XPS method.

[0037] According to a preferred embodiment of any technical solution of the fourth aspect of the present invention, the Li of the niobate two-dimensional film... + / Na + The separation ratio is greater than 5; the K of the niobate two-dimensional membrane + / Na + The separation ratio is greater than 5. Preferably, the Li in the niobate two-dimensional membrane... + / Na + The separation ratio is greater than 10; the K of the niobate two-dimensional membrane + / Na + The separation ratio is greater than 10. More preferably, the Li in the niobate two-dimensional film... + / Na + The separation ratio is greater than 20; the K of the niobate two-dimensional membrane + / Na + The separation ratio is greater than 20. For example, the Li-type niobate two-dimensional membrane. + / Na + The separation ratio is selected from 5~45, 5~40, 10~40, or 20~40; the K of the niobate two-dimensional membrane + / Na + The separation ratio is selected from 5~70, 5~60, 10~55, or 20~55.

[0038] 【5. Preparation method of niobate two-dimensional membranes】 The fifth aspect of the present invention provides a method for preparing a two-dimensional niobate membrane according to any of the technical solutions of the fourth aspect of the present invention, comprising the step of filtration of the niobate nanosheets onto a substrate.

[0039] Preferably, the substrate can be a nylon substrate.

[0040] 6. Application of niobate two-dimensional membranes in the separation of alkali metal ions The sixth aspect of the present invention provides the application of the niobate two-dimensional membrane described in any of the technical solutions of the fifth aspect of the present invention in the separation of alkali metal ions.

[0041] According to any of the technical solutions of the sixth aspect of the present invention, the alkali metal ion is Na. + The application is from a source containing Na + Separating Na from the system + .

[0042] According to any of the technical solutions of the sixth aspect of the present invention, the Na-containing + The system is selected from one of the following systems: Na + / K + ; Na + / Li + ; Na + / K + / Li + .

[0043] According to any of the technical solutions of the sixth aspect of the present invention, the alkali metal ion is K. + and Li + The application is from a source containing K + and Li + Separating K from the system + and Li + .

[0044] According to any of the technical solutions of the sixth aspect of the present invention, the alkali metal ion is K. + The application is from a source containing K + And it does not contain Li + Separating K from the system + .

[0045] According to any of the technical solutions of the sixth aspect of the present invention, the alkali metal ion is Li + The application is from Li + And does not contain K + Separating Li from the system + .

[0046] In the aforementioned alkali metal ion system, niobate two-dimensional membranes retain Na + Li + / K + Priority approval.

[0047] In K + / Na + In the binary system, niobate two-dimensional films exhibit the highest 45.8 (K) + / Na + The separation factor of ) and in Li + / Na + In the binary system, niobate two-dimensional films exhibit the highest performance at 33.1 (Li + / Na + The separation factor is an order of magnitude higher than that of state-of-the-art alkali metal ion separation membranes (such as MXene-PDA membranes).

[0048] 7. Niobate / graphene oxide composite nanosheets Surprisingly, this invention reveals that, unlike the interlayer structure of "V"-shaped and "Z"-shaped channels formed when niobate nanosheets are used alone to form niobate two-dimensional films, when niobate nanosheets and graphene oxide nanosheets are used to form composite nanosheets and further fabricated into composite two-dimensional films, the "V"-shaped channels of niobate in the composite two-dimensional film are blocked by the graphene oxide nanosheets, resulting in only "Z"-shaped channels in the composite two-dimensional film, without the "V"-shaped channels. The retention of regular "Z"-shaped channels in the composite two-dimensional film is beneficial for the preferential passage of lithium ions. Therefore, using niobate nanosheets and graphene oxide nanosheets to form composite nanosheets can serve as a raw material for preparing composite two-dimensional films that allow preferential passage of lithium ions.

[0049] Based on the above, the seventh aspect of the present invention provides a niobate / graphene oxide composite nanosheet, wherein the composite nanosheet comprises potassium niobate nanosheets and graphene oxide nanosheets. In the potassium niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 5 nm and a maximum lateral dimension of 100 nm or more, preferably 0.1 to 10 μm, more preferably 1 to 7 μm, and most preferably 2 to 6 μm.

[0050] In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1.5 nm and a maximum lateral dimension of greater than or equal to 100 nm, preferably 0.1~10 μm, further preferably 1~7 μm, and most preferably 2~6 μm.

[0051] It should be noted that the 80% mentioned here refers to the number of nanosheets. Typically, when observing steps with a thickness greater than 1 nm in atomic force microscopy (AFM), the number of nanosheets in the observed area should be no less than 20. When preparing the sample for AFM observation, niobate nanosheets are dispersed in a volatile solvent (concentration approximately 0.3 mg / mL). A drop is placed onto the support, and after the solvent evaporates, AFM testing is performed to observe the thickness and size of the sample.

[0052] It should also be noted that the thickness of a single layer of graphene oxide is generally 0.7 nm.

[0053] Preferably, in the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 3 nm and a maximum lateral dimension of 100 nm or more, preferably 0.1 to 10 μm, further preferably 1 to 7 μm, and most preferably 2 to 6 μm.

[0054] In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1 nm and a maximum lateral dimension of greater than or equal to 100 nm, preferably 0.1~10 μm, further preferably 1~7 μm, and most preferably 2~6 μm.

[0055] According to a preferred embodiment of any technical solution of the seventh aspect of the present invention, the niobium mass percentage in the composite nanosheet is 16.15% to 50.13%; A seventh aspect of the present invention provides another niobate / graphene oxide composite nanosheet, wherein the composite nanosheet comprises niobate nanosheets and graphene oxide nanosheets; The mass ratio of niobate nanosheets to graphene oxide nanosheets is (0.4-4.5):1, preferably (1.5-4.5):1, further preferably (2-4):1, even more preferably (2.5-3.5):1, and most preferably (3±0.2):1.

[0056] Preferably, in the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 5 nm and the maximum lateral dimension of the niobate nanosheets is greater than or equal to 100 nm; In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1.5 nm and the maximum lateral dimension of the graphene oxide nanosheets is greater than or equal to 100 nm.

[0057] More preferably, the maximum lateral dimension of the niobate nanosheets is 0.1–10 μm, more preferably 1–7 μm, and most preferably 2–6 μm. The maximum lateral dimension of the graphene oxide nanosheets is preferably 0.1–10 μm, more preferably 1–7 μm, and most preferably 2–6 μm. Larger-sized two-dimensional materials exhibit better long-range order when used to construct two-dimensional films.

[0058] According to a preferred embodiment of any of the seventh aspects of the present invention, in the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 3 nm and the maximum lateral dimension of the niobate nanosheets is greater than or equal to 100 nm. In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1 nm and the maximum lateral dimension of the graphene oxide nanosheets is greater than or equal to 100 nm.

[0059] When AFM detects a thickness of less than 3 nm for niobate nanosheets, the niobate nanosheets typically consist of a single layer. Single-layer niobate nanosheets, compared to those with two or more layers, are more likely to form herringbone channels when constructing two-dimensional films, exhibiting superior K0 properties. + Li + Exchange capacity.

[0060] 8. Dispersion of niobate / graphene oxide composite nanosheets The eighth aspect of the present invention provides a dispersion of niobate / graphene oxide composite nanosheets containing any of the technical solutions of the seventh aspect of the present invention, wherein the dispersion medium of the dispersion contains water.

[0061] According to a preferred embodiment of any technical solution of the eighth aspect of the present invention, the mass concentration of the dispersed phase in the dispersion is 0.01~100 mg / mL, preferably 0.1~10 mg / mL, more preferably 0.1~5 mg / mL, and most preferably 0.1~1 mg / mL. When the mass concentration of the dispersed phase is too high, the dispersed phase is prone to agglomeration.

[0062] [9. Preparation method of dispersion of niobate / graphene oxide composite nanosheets] The ninth aspect of this invention provides a method for preparing a dispersion of niobate / graphene oxide composite nanosheets according to any of the technical solutions of the seventh aspect of this invention, or according to any of the technical solutions of the eighth aspect of this invention, comprising the following steps: A dispersion containing niobate nanosheets and a dispersion containing graphene oxide nanosheets were mixed.

[0063] According to a preferred embodiment of any technical solution of the ninth aspect of the present invention, the mass concentration of niobate nanosheets in the dispersion containing niobate nanosheets is 0.01~100 mg / mL, preferably 0.1~10 mg / mL, further preferably 0.1~5 mg / mL, and most preferably 0.1~1 mg / mL; The mass concentration of graphene oxide nanosheets in the dispersion containing graphene oxide nanosheets is 0.01~100 mg / mL, preferably 0.1~10 mg / mL, more preferably 0.1~5 mg / mL, and most preferably 0.1~1 mg / mL.

[0064] According to a preferred embodiment of any of the ninth aspects of the present invention, the method for preparing the dispersion of niobate nanosheets includes the following steps: Soaking steps: Add M4Nb6O 17 The crystals are immersed in an acidic solution to obtain an acidic dispersion; M is selected from K, Na, or Li; Intercalation step: The acidic dispersion is subjected to hydrothermal intercalation to obtain an intercalated dispersion; Microfluidization step: The intercalated dispersion is microfluidized using a microfluidic jet injector to obtain a microfluidized dispersion; Centrifugation step: The microfluidic dispersion is centrifuged to obtain a dispersion of niobate nanosheets.

[0065] According to a preferred embodiment of any technical solution of the ninth aspect of the present invention, in the microfluidization step, the pressure of the microfluidic ejector is 500~2000 bar, and the microfluidization treatment time is 0.5~10 h. Preferably, the pressure of the microfluidic ejector is 800~1600 bar, and the microfluidization treatment time is 1~8 h. More preferably, the pressure of the microfluidic ejector is 1000~1400 bar, and the microfluidization treatment time is 2~6 h.

[0066] 【10. Niobate / graphene oxide composite two-dimensional film】 As described above, this invention is the first to discover that, unlike the interlayer structure of the "V"-shaped and "Z"-shaped channels formed in niobate two-dimensional films, the "V"-shaped channels of niobate are blocked by graphene oxide nanosheets in the niobate / graphene oxide composite two-dimensional film, resulting in a composite two-dimensional film containing only "Z"-shaped channels and no "V"-shaped channels. Since the retention of "Z"-shaped channels in the composite two-dimensional film facilitates the preferential passage of lithium ions, K0 can be achieved. + / Li + Na + / Li + Or Na + / K + / Li +Separation of lithium ions in the system.

[0067] Based on this, the tenth aspect of the present invention provides a niobate / graphene oxide composite two-dimensional film, wherein the composite two-dimensional film comprises niobate nanosheets and graphene oxide nanosheets; The maximum lateral dimension of more than 80% of the niobate nanosheets and graphene oxide nanosheets is greater than or equal to 100 nm, preferably 0.1~10 μm, more preferably 1~7 μm, and most preferably 2~6 μm; In the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 5 nm; In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1.5 nm; The thickness of the composite two-dimensional film is 0.05~10 μm, preferably 0.1~9 μm, and more preferably 0.5~6 μm.

[0068] Under certain preferred conditions, in Li + / K + In the binary system, the niobate / graphene oxide composite two-dimensional film exhibits the highest Li-value of 27.8. + / K + The separation factor is much higher than that reported in the prior art.

[0069] According to a preferred embodiment of any technical solution of the tenth aspect of the present invention, in the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 3 nm; In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1 nm.

[0070] It is worth noting that when the ratio of niobate nanosheets to graphene oxide nanosheets in the niobate / graphene oxide composite two-dimensional film is within a certain range, the blockage of the "human" shaped channel can be achieved. Simply put, the ratio of niobate nanosheets to graphene oxide nanosheets can be controlled by controlling the content of niobium in the two-dimensional film. When the mass percentage of niobium in the composite two-dimensional film is 16.15% to 50.13%, the above requirements can be met.

[0071] According to a preferred embodiment of any technical solution of the tenth aspect of the present invention, the mass percentage of niobium in the composite two-dimensional membrane is 16.15% to 50.13%.

[0072] The tenth aspect of the present invention provides a niobate / graphene oxide composite two-dimensional film, the composite two-dimensional film comprising niobate nanosheets and graphene oxide nanosheets; the mass ratio of the niobate nanosheets to the graphene oxide nanosheets is (0.4-4.5):1, preferably (1.5-4.5):1, further preferably (2-4):1, even more preferably (2.5-3.5):1, and most preferably (3±0.2):1; The maximum lateral dimension of more than 80% of the niobate nanosheets and graphene oxide nanosheets is greater than or equal to 100 nm, preferably 0.1~10 μm, more preferably 1~7 μm, and most preferably 2~6 μm; In the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 5 nm; In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1.5 nm; The thickness of the composite two-dimensional film is 0.05~10 μm, preferably 0.1~9 μm, and more preferably 0.5~6 μm.

[0073] According to a preferred embodiment of any technical solution of the tenth aspect of the present invention, the Li of the niobate / graphene oxide composite two-dimensional film... + / K + The separation ratio is greater than 5. Preferably, the Li in the niobate / graphene oxide composite two-dimensional film... + / K + The separation ratio is greater than 10. More preferably, the Li in the niobate / graphene oxide composite two-dimensional film... + / K + The separation ratio is greater than 20. For example, the Li in the niobate / graphene oxide composite two-dimensional film. + / K + The separation ratio is selected from 5~40, 5~35, 10~35, 20~30 or 25~30.

[0074] 【11. Preparation method of niobate / graphene oxide composite two-dimensional film】 The eleventh aspect of the present invention provides a method for preparing a niobate / graphene oxide composite two-dimensional membrane, comprising the step of filtration of the niobate / graphene oxide composite nanosheets onto a substrate.

[0075] Preferably, the substrate can be a nylon substrate.

[0076] 【12. Application of niobate / graphene oxide composite two-dimensional membranes in the separation of alkali metal ions】 The twelfth aspect of this invention provides the application of a niobate / graphene oxide composite two-dimensional membrane in the separation of alkali metal ions; preferably, the alkali metal ion is Li. +The application is from Li + Separating Li from the system + Further preferably, the substance containing Li + The system is selected from one of the following systems: K + / Li + Na + / Li + Or Na + / K + / Li + The system. In the above alkali metal ion system, the niobate / graphene oxide composite two-dimensional film allows Li + Priority approval.

[0077] As mentioned earlier, under certain preferred conditions, in Li + / K + In the binary system, the niobate / graphene oxide composite two-dimensional film exhibits the highest Li-value of 27.8. + / K + The separation factor is much higher than that reported in the prior art.

[0078] 【13. Two-dimensional membrane assembly equipment】 Based on the aforementioned ability of niobate two-dimensional membranes to retain sodium ions, and niobate / graphene oxide composite two-dimensional membranes to retain potassium ions, using these two membranes in series can achieve the acquisition of specific ions from various alkali metal ions. For example, in Na+... + / K + / Li + To achieve lithium-ion separation and enrichment in the system.

[0079] Based on this, the thirteenth aspect of the present invention provides a two-dimensional membrane assembly device, the two-dimensional membrane assembly device comprising a niobate two-dimensional membrane and a niobate / graphene oxide composite two-dimensional membrane connected in series; The niobate two-dimensional film comprises niobate nanosheets; In the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 5 nm and a maximum lateral dimension of 100 nm or more, preferably 0.1~10 μm, more preferably 1~7 μm, and most preferably 2~6 μm; The thickness of the niobate two-dimensional film is 0.05~10 μm, preferably 0.1~9 μm, and more preferably 0.5~6 μm; Herman orientation factor of the niobate two-dimensional film f Not less than 0.9; The niobate / graphene oxide composite two-dimensional film is the niobate / graphene oxide composite two-dimensional film described in any embodiment of the tenth aspect of this invention.

[0080] According to a preferred embodiment of any of the technical solutions described in the thirteenth aspect of the present invention, the number of niobate two-dimensional membranes in the two-dimensional membrane assembly device is one or more; the number of niobate / graphene oxide composite two-dimensional membranes in the two-dimensional membrane assembly device is one or more.

[0081] When the number of niobate two-dimensional membranes is greater than 1, the lithium ion content in the ions passing through the two-dimensional membrane will gradually increase with the increase of the number of niobate two-dimensional membranes; when the number of niobate / graphene oxide composite two-dimensional membranes is greater than 1, the lithium ion content in the ions passing through the two-dimensional membrane will further increase with the increase of the number of niobate / graphene oxide composite two-dimensional membranes, thus achieving the enrichment and separation of lithium ions.

[0082] 【14. Application of two-dimensional membrane combination equipment in the separation of alkali metal ions】 The fourteenth aspect of the present invention provides the application of the two-dimensional membrane assembly device of the thirteenth aspect of the present invention in the separation of alkali metal ions, wherein the alkali metal ions are Li + The application is from Li + Separating Li from the system + The one containing Li + The system contains Na + / Li + or K + / Li + Or Na + / K + Or Na + / K + / Li + The system, especially containing Na. + / K + / Li + The system.

[0083] According to a preferred embodiment of any of the technical solutions described in the fourteenth aspect of the present invention, the alkali metal ions first pass through a niobate two-dimensional membrane, and then through a niobate / graphene oxide composite two-dimensional membrane. When passing through the niobate two-dimensional membrane first, Na... + The retention of Na resulted in the separation of Na. + ; and then, by using a niobate / graphene oxide composite two-dimensional film, Ka can be achieved. + The retention and separation of K + Neither of the two two-dimensional films retains Li. + Ultimately, Li + Enrichment and separation.

[0084] Under certain preferred conditions, in Li + / K + / Na +In a ternary system, a combination of niobate two-dimensional membranes and niobate / graphene oxide composite two-dimensional membranes can achieve the enrichment and separation of lithium ions, with a lithium ion abundance of over 90%.

[0085] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention first prepared a two-dimensional niobate membrane using monodisperse niobate nanosheets. For the first time, ACTEM was used to observe "V"-shaped and "Z"-shaped channels between the two-dimensional niobate membrane layers. Experiments showed that the regular "V"-shaped channels allowed lithium or potassium ions to pass preferentially with low resistance, while the regular "Z"-shaped channels allowed lithium ions to pass preferentially but with high resistance. The two channels also showed resistance to Na+. + All exhibited specific inhibitory effects, making them effective in Li + and / or K + with Na + When coexisting, the niobate two-dimensional film can achieve the protection of Na+. + The retention. Under some preferred conditions, in K + / Na + In the binary system, niobate two-dimensional films exhibit the highest 45.8 (K) + / Na + The separation factor of ) and in Li + / Na + In the binary system, niobate two-dimensional films exhibit the highest performance at 33.1 (Li + / Na + The separation factor mentioned above is much higher than the separation factor reported in the prior art.

[0086] (2) In another aspect, the present invention uses niobate / graphene oxide composite nanosheets formed by monodisperse niobate nanosheets and graphene oxide nanosheets to prepare niobate / graphene oxide composite two-dimensional films. Surprisingly, the present invention discovers that, unlike the interlayer structure of the "V"-shaped and "Z"-shaped channels formed when niobate nanosheets are used alone to form niobate two-dimensional films, when niobate nanosheets and graphene oxide nanosheets are used to form composite nanosheets and further fabricated into composite two-dimensional films, the "V"-shaped channels of niobate in the composite two-dimensional film are blocked by graphene oxide nanosheets, resulting in only "Z"-shaped channels in the composite two-dimensional film, and no longer allowing potassium ions to pass through. The retention of regular "Z"-shaped channels in the composite two-dimensional film is beneficial for the preferential passage of lithium ions. Therefore, this composite two-dimensional film can achieve K... + / Li + Or Na + / Li + Or Na + / K + / Li +Lithium ion separation in a system. Under certain preferred conditions, in K + / Li + In the binary system, the composite two-dimensional film exhibits the highest 27.8 (Li) + / K + The separation factor.

[0087] (3) Based on the aforementioned niobate two-dimensional membrane's ability to retain sodium ions, and the niobate / graphene oxide composite two-dimensional membrane's ability to retain potassium ions, this invention, in another aspect, uses these two membranes in series to achieve the acquisition of specific ions from various alkali metal ions. For example, in Na... + / K + / Li + In the system, a two-dimensional niobate membrane is first used to retain Na. + Then, a niobate / graphene oxide composite two-dimensional film is used to retain K. + , obtain Li + This method can extract lithium ions from alkali metal ions, achieving the separation and enrichment of lithium ions. The significance of this cascade separation strategy in this field lies in breaking through the traditional separation upper limit based on static ion properties (such as size, dehydration energy barrier, or Donnan repulsion), providing a highly efficient and stable nanochannel cascade system, which is particularly suitable for the extraction and enrichment of lithium resources in complex salt lake brine systems.

[0088] (4) In the method for preparing monodisperse niobate nanosheets in this invention, a microfluidization step is used for the first time. The intercalated dispersion is microfluidized by a microfluidic jet to obtain a microfluidized dispersion. Under this condition, the niobate nanosheets obtained are larger in size and have fewer layers (single layer or a small number of double layers), which is conducive to forming niobate nanosheets with a larger length-to-thickness ratio. When large-sized two-dimensional materials are used to construct two-dimensional films, they have better long-range order.

[0089] (5) The significance of this invention lies in achieving precise separation of alkali metal ions by controlling the structural symmetry (herringbone or zigzag) of niobate nanochannels, thus paving the way for the sustainable acquisition of strategic metal ion resources. Attached Figure Description

[0090] Figure 1 middle: a is a schematic diagram of the H-shaped cell used for measuring the permeation rate of the unicomponent system of the present invention; b is a schematic diagram of the H-shaped cell used for determining the separation ratio of the binary system in this invention; Figure 2 middle: a is the product obtained in Example 1 of this invention. m- KN nanosheet dispersion (diluted approximately 20 times) m -Partial atomic force microscopy (AFM) image of KN nanosheets; b is the product obtained in Example 1 of this invention. m- KN nanosheet dispersion (undiluted) m -Partial atomic force microscopy (AFM) image of KN nanosheets; c represents the product obtained in Example 1 of this invention. m- KN nanosheet dispersion (diluted approximately 20 times) m - Atomic resolution image of KN nanosheets obtained by field emission transmission electron microscopy (FETEM); in the upper right inset, the gray area is a simulated (TEM) image, and the green area is K4Nb6O. 17 Structure diagram created from a CIF file of a crystal; d represents the sample prepared in Example 1 of this invention. m- KN nanosheet dispersion (diluted approximately 20 times) m Atomic resolution images of KN nanosheets obtained by transmission electron microscopy (TEM); Figure 3 middle: a is the preparation obtained in Example 1 of the present invention. m -KN nanosheets and Comparative Example 1 were prepared to obtain p -Thickness distribution diagram of KN nanosheets; b is the preparation obtained in Example 1 of this invention. m -KN nanosheets and Comparative Example 1 were prepared to obtain p - Maximum lateral size distribution diagram of KN nanosheets; Figure 4 The preparation of Comparative Example 1 of this invention p -KN nanosheet dispersion (diluted approximately 10 times) p -Partial atomic force microscopy (AFM) image of KN nanosheets; Figure 5 middle: a is the product obtained in Example 2 of this invention. m- Aberration-corrected transmission electron microscope (ACTEM) image of the cross-section of the KN two-dimensional membrane; b is the preparation obtained in Example 2 of this invention. m- Field emission scanning electron microscopy (FESEM) image of a cross-section of a KN two-dimensional film (approximately 5 μm thick); the inset in the upper left corner is... m- Photograph of a KN two-dimensional membrane (approximately 5 μm thick); c represents the product obtained in Example 2 of this invention. m- X-ray scattering (WAXS) spectrum of a KN two-dimensional film (approximately 5 μm thick); d represents the sample prepared in Example 2 of this invention. m-X-ray diffraction (XRD) patterns of a KN two-dimensional membrane (approximately 1 μm thick) before and after permeation rate measurement in a uni-component system; Figure 6 middle: a represents the sample prepared in Comparative Example 2 of this invention. p- Field emission scanning electron microscopy (FESEM) image of a cross-section of a KN two-dimensional film; the inset in the upper left corner is... p- Photographs of KN two-dimensional membranes; b represents the sample prepared according to Comparative Example 2 of this invention. p- X-ray scattering (WAXS) spectrum of KN two-dimensional film; Figure 7 middle: a represents the different aspects in Embodiment 3 of the present invention. m- KN / GO mass ratio m- KN-GO two-dimensional film Li under uni-component system conditions + / K + Selectivity diagram; b represents a different embodiment 3 of the present invention. m- KN / GO mass ratio m- X-ray diffraction (XRD) pattern of KN-GO two-dimensional film; c represents the third embodiment of the present invention. m- KN-GO two-dimensional membrane ( m- Aberration-corrected transmission electron microscope (ACTEM) image of the cross section of a KN / GO mass ratio of 3:1; where the black dots represent graphene oxide (GO). d represents the third embodiment of the present invention. m- KN-GO two-dimensional membrane ( m- X-ray diffraction (XRD) patterns of a unicomponent system with a KN / GO mass ratio of 3:1 before and after the permeation rate measurement. It should be noted that KN-GO in the diagram represents m- KN-GO two-dimensional membrane; Figure 8 middle: a represents the different examples in Comparative Example 3 of this invention. m- The mass ratio of KN / PSS under univariate system conditions K + / Na + Selectivity diagram; b represents Comparative Example 3 of this invention. m- KN-PSS two-dimensional membrane ( m- Scanning electron microscope (SEM) image of the cross section of a KN / PSS mass ratio of 1:3; Figure 9 middle: a is the product obtained in Example 2 of this invention. m-Comparison of permeation rates of different ions under uni-component system conditions of KN two-dimensional membrane (thickness approximately 1 μm); b is the preparation obtained in Example 3 of this invention. m- KN-GO two-dimensional membrane ( m- A comparison of the permeation rates of different ions under the condition of a KN / GO mass ratio of 3:1; c represents the sample prepared in Comparative Example 2 of this invention. p- Comparison of permeation rates of different ions under the condition of KN two-dimensional membrane uni-component system; Figure 10 The sample prepared in Example 2 of this invention m- KN two-dimensional membranes (approximately 1 μm thick) are compared with nylon, Mg-AlLDH, MXene, GO, and Vermiculite two-dimensional membranes. + Li + A comparison chart of permeation rates; Figure 11 The sample prepared in Example 2 of this invention m- The KN two-dimensional film (approximately 1 μm thick) and the film prepared in Example 3 of this invention m- KN-GO two-dimensional membrane ( m- A bar chart showing the stability of separation performance in a binary system with a KN / GO mass ratio of 3:1. It should be noted that KN-GO in the diagram represents m- KN-GO two-dimensional membrane; Figure 12 This is a trend graph of lithium-ion abundance under ternary system conditions in Test Examples 1-3 of this invention; Figure 13 middle: a is the product obtained in Example 2 of this invention. m- Powder X-ray diffraction (PXRD) patterns of a KN two-dimensional film (approximately 1 μm thick) placed in water before and after 24 h; b represents the sample prepared according to Comparative Example 2 of this invention. p- Powder X-ray diffraction (PXRD) images of a KN two-dimensional film (approximately 1 μm thick) placed in water for 24 h before and after immersion. Detailed Implementation

[0091] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0092] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0093] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0094] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as "less than about 4.5," which should be interpreted to include all the values ​​and ranges described above. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0095] It should be noted that the hydrothermal intercalation method refers to existing technology (Baudouin F. Synthesis and transfer of nanosheets seed layers on various substrates for the preferentially oriented growth of complex oxides thin films[D]. Université de Rennes, 2021.). The present invention will be further described below with reference to specific embodiments.

[0096] Materials used in preparation: KMoO4, Nb2O5, n-propylamine, tetrabutylammonium hydroxide (TBAOH), and sodium polystyrene sulfonate (PSS) were purchased from Sigma-Aldrich; K2CO3 and 12 M concentrated hydrochloric acid were commercially available, and 6 M hydrochloric acid was obtained by diluting 12 M concentrated hydrochloric acid; graphene oxide (GO) was prepared according to the existing technology (Nature Nanotechnology 12, 546–550 (2017)).

[0097] Test method: 1. Herman Orientation Factorf The determination of ) (1) The overall orientation of the film was measured using wide-angle X-ray scattering (WAXS) spectroscopy, and its azimuth angle was fitted. φ Figure 1 shows the evaluation of the ordering of nanosheets in the niobate two-dimensional film. The WAXS experiment was conducted using a Xenocs Xeuss SAXS / WAXS system equipped with a Cu-Kα radiation source and a Pilatus 3R 300K detector. The sample sheet of the niobate two-dimensional film was 10 mm in length and width, and the X-ray beam was oriented nearly parallel to the plane of the sample sheet, which was placed at a distance of 163.5 mm from the detector. X-rays were captured in WAXS scattering mode using a Pilatus 3R 300k detector.

[0098] (2) Herman orientation factor f Calculation of ) using the Herman orientation factor ( f The alignment degree of nanosheets within the sample is quantified by the Herman orientation factor. f The definition is as follows: (S1) in, (S2) in cos 2 φ It is the average of the squares of the azimuth cosines of the (040) peak of the niobate two-dimensional film sample. I ( φ ) is in φ Intensity at the azimuth angle.

[0099] 2. Determination of the permeation rate of a single-component system: A two-dimensional membrane is sandwiched between a pair of polyethylene terephthalate (PET) cover layers with circulation windows (approximately 8 mm in diameter) and sealed with epoxy resin at the junction of the H-shaped pool, as shown. Figure 1 As shown in (a), one side of the H-shaped cell is a packed chamber (FC) and the other side is a permeation chamber (PC). A 0.2 M aqueous solution of metal ion chloride is filled into the packed chamber (FC); the conductivity meter electrode is inserted into the permeation chamber, and ultrapure water (DI, resistivity: 18.2 MΩ) is added until the liquid level is the same as the liquid level in the packed chamber. Test settings: The test duration is 14400 s, and the conductivity value is taken every 60 s. For salt solutions containing different metal ions, the ion concentration in the osmosis chamber was monitored over time. (t)The slope of the slope can be used to obtain the permeation rate (P, in mol·m⁻¹) of alkali metal ions. –2 ·h –1 ): (S3) Where A represents the effective membrane area (m²) 2 ); V This indicates the volume (L) of the aqueous solution in the permeation chamber (PC). C alkali This is based on data obtained from SevenMulti™ dual-gauge (METTLER TOLEDO). C alkali The concentration of alkali metal ions is calculated from the standard curve between the alkali metal ion concentration and the ionic conductivity (σ).

[0100] Ideal permeability selection ( α ideal The ratio of the osmotic rates of ions A and B is equal to the ratio of their osmotic rates. (S4) 3. Determination of the separation ratio of a binary system: To maintain the same ionic strength in the FC, a mixture of two alkali metal chloride aqueous solutions, each with a concentration of 0.1 M, was used as the feed, and HCl with an equal chloride ion concentration was added to the PC to counteract concentration polarization. For example... Figure 1 As shown in (b), in the binary system, the ion concentration of alkali metal ions and the permeation rate were determined by ion chromatography (Eco IC, Metrohm) according to ASTM standard D6919-17, and the system was calibrated against a standard sample before testing, as described below: (S5) (S6) C i molar concentration (mol·L) –1 ); m i Indicates ion mass concentration (ppm); M i Indicates the molar mass of an ion; Permeation rate (mol·m) –2 ·h –1 ); C 1 indicates the ion concentration at the time of the first measurement. C 2 indicates the ion concentration during the second measurement; V This indicates the volume (L) of the aqueous solution in the permeation chamber (PC). A Represents the effective membrane area (m²) 2 ); t This indicates the time interval between the first and second measurements.

[0101] The ion selectivity of a binary system is defined as: (S7) 4. Determination of separation in ternary systems: A ternary mixture solution of LiCl, NaCl, and KCl, each with a concentration of 0.067 M, was used as the feed and loaded into 1... st FC room, will m -KN membrane is used as the first-stage separation membrane in 1 st The PC chamber is filled with an equal volume of HCl at the same chloride ion concentration. Similar to the separation of the binary system described above, ion chromatography is also used to measure 1. st The concentrations of each alkali metal ion in the PC chamber solution; according to 1 st The abundance ratio of each alkali metal ion in the PC chamber was determined, and a new solution with the same abundance ratio and a total alkali metal ion concentration of 0.2 M was prepared. 2 nd FC room, with m -KN membrane as the second-stage separation membrane, similarly, 2 nd The PC chamber is filled with an equal volume of HCl at an equal chloride ion concentration. Similarly, the abundance ratio of each alkali metal ion in the FC chamber is always maintained the same as that in the previous stage PC chamber, and the total alkali metal ion concentration is 0.2 M. The third-stage separation membrane uses... m -KN membrane, the 4th and 5th stage separation membranes are used m- KN-GO membrane.

[0102] Example 1 This embodiment provides a method for preparing monodisperse potassium niobate nanosheets (denoted as...). m- The preparation method of KN nanosheets specifically includes the following steps: S1: Add K2CO3, KMoO4 and Nb2O5 in a molar ratio of 2:19:3 to a ball mill and mix them evenly to obtain a mixture; S2: The mixture was placed in an alumina crucible in a muffle furnace. The muffle furnace was heated from room temperature to 1100 °C at a heating rate of 43 °C / min and held at that temperature for 24 hours. Subsequently, the temperature inside the muffle furnace was reduced to 500 °C at a cooling rate of 5 °C / min, and then allowed to cool naturally to room temperature to obtain centimeter-scale K4Nb6O. 17 Crystals; S3: Take 0.1 g of K4Nb6O 17 The crystals were immersed in 50 mL of 6 M HCl and shaken thoroughly for 3 days to obtain K4Nb6O. 17 Hydrochloric acid dispersion; S4: The K4Nb6O obtained in S3 17 The hydrochloric acid dispersion was transferred to a 100 mL Teflon beaker, and 22 mL of n-propylamine solution (n-propylamine to water volume ratio of 1:10) was added for hydrothermal intercalation at 120 °C for 3 days, yielding the intercalated dispersion (K). 4-x H x Nb6O 17 ); S5: The intercalation dispersion (K) was prepared using a microfluidic injector (NLM100, Ilshin Autoclave) at 1200 bar. 4- x H x Nb6O 17 Microfluidize for 4 hours to obtain a microfluidic dispersion.

[0103] S6: Centrifuge the microfluidic dispersion at 1000 rpm (Multifuge X1R, ThemoFisher) for 10 min to remove unexfoliated portions, obtaining monodisperse potassium niobate nanosheets (denoted as...). m- KN nanosheet dispersion, with a concentration controlled at 0.3 mg / mL.

[0104] Characterization: The following results were obtained using atomic force microscopy (AFM, with a tip force constant of 10⁻¹³⁰ N / m). m -Atomic force microscopy (AFM) image of KN nanosheets, with a partial AFM image as shown below. Figure 2 a (diluted approximately 20 times) and Figure 2 As shown in b (undiluted), the AFM results show that... m- KN nanosheets are mainly composed of one layer (2 nm thick) or two layers (4 nm thick). Regarding... m -Atomic force microscopy measurements and statistical analysis of KN nanosheets were obtained. m -KN nanosheet thickness distribution as shown Figure 3 As shown in figure a, the maximum lateral dimension distribution is as follows Figure 3 As shown in b; from Figure 3 a and Figure 3 b shows that m- More than 80% of the two-dimensional nanosheets in KN nanosheets have a thickness of less than 2 nm, which are monodisperse potassium niobate nanosheets; at the same time, nearly 60% of the two-dimensional nanosheets have a maximum lateral dimension between 1 and 3 μm.

[0105] Obtained using field emission transmission electron microscopy (FETEM) and transmission electron microscopy (TEM) m Atomic resolution images of KN nanosheets, such as Figure 2 As shown in cd, where... Figure 2The gray area in the upper right corner of the illustration is a simulated (TEM) image, and the green area is K4Nb6O. 17 The structure diagram is created from the crystal's CIF file. Figure 2 As can be seen from c, m Transmission electron microscopy (FETEM) images of the KN nanosheets show a clear two-dimensional morphology, indicating... m -KN nanosheets are uniform monolayers. From Figure 2 As can be seen from d, m The lattice on the surface of the KN nanosheets is essentially consistent with the simulated (TEM) image, further illustrating... m -KN nanosheets are single-layer nanosheets, and also two-dimensional. m -KN has an orthogonal lattice along the (010) axis (a=0.78 nm, c=0.64 nm), which is consistent with the periodicity of the niobium-oxygen octahedral zigzag assembly of the bilayer structure.

[0106] The typical mass concentration of monodisperse potassium niobate nanosheets in the dispersion is in the range of 0.1~100 mg / mL. Excessive mass concentration will lead to agglomeration.

[0107] from Figure 2 ad and Figure 3 As can be seen from ab, the microfluidic method prepares... m -KN nanosheets are characterized by being monodisperse, thin, and having large lateral dimensions, providing ideal building blocks with periodic nanoconfined space for constructing differentiated ion channels.

[0108] Comparative Example 1 This comparative example provides a method for preparing polydisperse niobate nanosheets. p The preparation method of (-KN nanosheets) is the same as that in Example 1 for S1~S3, except that: S4: Tetrabutylammonium hydroxide (TBAOH) was dissolved in 20 mL of deionized water to obtain a 12.5 wt% tetrabutylammonium hydroxide solution, and then reacted with the K4Nb6O obtained in S3. 17 The hydrochloric acid dispersion was mixed in a 100 mL Teflon beaker for hydrothermal intercalation at a temperature of 120 °C for 3 days to obtain the intercalated dispersion. S5: Centrifuge the intercalated dispersion at 1000 rpm (Multifuge X1R, ThemoFisher) for 10 min to remove unexfoliated portions, obtaining polydisperse potassium niobate nanosheets (denoted as...). p- KN nanosheet dispersion, with a concentration controlled at 0.3 mg / mL.

[0109] Characterization: p -Atomic force microscopy measurements and statistical analysis of KN nanosheets were obtained.p -KN nanosheet thickness distribution as shown Figure 3 As shown in figure a, the maximum lateral dimension distribution is as follows Figure 3 As shown in b, it can be seen from the figure that the thickness of the untreated niobate nanosheets is mainly distributed in the range of 3-10 nm. Figure 3 a) The maximum lateral dimension of the nanosheets is 15-20 μm (a) Figure 3 (b) indicates that polydisperse potassium niobate nanosheets were obtained using conventional synthesis methods. This was confirmed by atomic force microscopy (AFM, tip force constant 10⁻¹³⁰ N / m). p -Atomic force microscopy (AFM) image of KN nanosheets, with a partial AFM image as shown below. Figure 4 (Diluted approximately 10 times) as shown.

[0110] Example 2 This embodiment is m- KN two-dimensional membrane, obtained from Example 1 m- KN nanosheet dispersions were vacuum filtered onto a nylon microporous substrate (Jinteng Company) with a pore size of 0.22 μm to prepare two sheets with thicknesses of approximately 1 μm and 5 μm. m- KN two-dimensional membrane.

[0111] Characterization: Field emission scanning electron microscopy (FESEM) was used to obtain a thickness of approximately 5 μm. m- FESEM cross-sectional image of the KN two-dimensional membrane is shown below. Figure 5 As shown in b, no defects, pores, or interlayer defects were found, indicating that the nanosheets were orderly assembled into regular channels. Wide-angle X-ray scattering (WAXS) spectroscopy measurements were performed. f The factor is 0.97, such as Figure 5 As shown in c, this indicates that the membrane as a whole possesses periodic ion channels, providing symmetrical niobate units for the interaction of hard-soft acid-base (HSAB) with alkali metal ions. Among currently known two-dimensional membrane materials, m -KN two-dimensional membrane f The values ​​exhibit a leading orderliness. m- A photograph of the KN two-dimensional membrane (approximately 5 μm thick) is shown below. Figure 5 As shown in the illustration in Figure b, the transparency indicates that the channels are more ordered and the nanosheets are stacked more regularly, providing a more intuitive demonstration. m - Orderliness of KN two-dimensional membranes.

[0112] Obtained using aberration-corrected transmission electron microscopy (ACTEM) m- An ACTEM cross-sectional image of a KN two-dimensional film (approximately 5 μm thick) is shown below. Figure 5 As shown in a. For m- XRD characterization was performed on a KN two-dimensional film (approximately 1 μm thick), such as... Figure 5As shown in the bottom image (d).

[0113] Using aberration-corrected transmission electron microscopy (ACTEM) and X-ray diffraction (XRD) to... m- Ion channels in the KN two-dimensional membrane were characterized. Similar to the bulk phase, in m- In the KN film, NbO6 layers can be observed to be symmetrically and orderly assembled in zigzag and herringbone patterns.

[0114] Comparative Example 2 This comparative example provides a... p- KN two-dimensional film, obtained by Comparative Example 1 p- KN nanosheets were prepared by vacuum filtration on a nylon microporous substrate (Jinteng Company) with a pore size of 0.22 μm. p- The thickness of the KN two-dimensional film is approximately 1 μm.

[0115] Characterization: Obtained using field emission scanning electron microscopy (FESEM) p- FESEM cross-sectional image of the KN two-dimensional membrane is shown below. Figure 6 As shown in figure a. Measurements were performed using wide-angle X-ray scattering (WAXS) spectroscopy. f The factor is 0.82, such as Figure 6 As shown in b, this indicates poor orderliness in the assembly. p- Photo of KN two-dimensional membrane as shown Figure 6 As shown in the illustration in Figure a, the blurred transparency indicates that the channels are irregular and the nanosheets are randomly stacked, which also visually demonstrates... p -KN two-dimensional membranes have poor order.

[0116] p -KN two-dimensional membranes exhibit various textures and interlayer pores in their layered structure, leading to significant expansion in water. Furthermore, in p In the KN two-dimensional film, the Herman orientation factor corresponding to the (040) crystal plane drops to 0.82, indicating that the niobate group has a low degree of order.

[0117] Example 3 This embodiment provides a m- Preparation of KN-GO two-dimensional membrane.

[0118] This invention discovers that incorporating monolayer graphene oxide (GO) nanosheets... m In a KN two-dimensional membrane, partial blocking is possible. m- The herringbone channel in the KN two-dimensional membrane; after the herringbone channel is blocked, K... + The penetration rate decreased, and based on this, this embodiment constructed... m- Prepared from KN monodisperse nanosheets and GO monodisperse nanosheets m-KN-GO two-dimensional membrane. By adjusting... m -KN (prepared in Example 1) and graphene oxide synthesized by the improved Hummer method were prepared in a mass ratio of 9:1 to 1:9. m- The KN-GO two-dimensional membranes all have a thickness of approximately 1 μm.

[0119] Screening for excellent Li + / K + Selective Transparency m- KN-GO membrane m- KN to GO mass ratio: Measurement of different m- Two-dimensional films obtained with KN / GO ratios (9:1~1:9) under unicomponent system conditions for Li + / K + Select permeability to evaluate m- The degree of blockage in the KN herringbone channel is used to screen for the optimal Li + / K + Selective Transparency m- KN / GO ratio.

[0120] The measurement results are as follows Figure 7 As shown in a, m- When the mass ratio of KN to GO is 3:1, Li + / K + Choose the option that maximizes permeability, i.e., Li + Priority is given to K, while K + Blocked, while at the same time m- XRD tests were performed on the KN-GO (3:1) two-dimensional film, such as... Figure 7 As shown in b, the XRD diffraction peaks corresponding to the herringbone channels disappear, indicating that the graphene oxide intercalation statistically blocks most of the herringbone channels, retaining only the zigzag channels that facilitate lithium ion passage. In contrast, other mass ratios... m The two-dimensional film formed by -KN and GO exhibits slightly lower Li... + / K + Selectivity, such as Figure 7 As shown in a. When m When the KN / GO mass ratio is higher than 3:1, some herringbone channels are not blocked, exhibiting characteristics similar to... m -KN membranes have similar low K content + / Li + Selectivity. However, when m When the KN / GO mass ratio is less than 3:1, the newly emerging ion channels are in K + and Li + The choice between them is non-selective, leading to Li + / K +The selectivity of Li decreases rapidly. Therefore, to improve Li + / K + With selectivity as the goal, m The optimal mass ratio of KN / GO is 3:1, based on which it is possible to build one Layer-by-layer assembly m- In the KN-GO membrane structure, the herringbone channels are blocked, leaving zigzag channels that dominate lithium-ion transport. Therefore, m- KN-GO membranes exhibit single lithium permeation selectivity.

[0121] Obtained using aberration-corrected transmission electron microscopy (ACTEM) m- ACTEM cross-sectional image of the KN-GO membrane is shown below. Figure 7 As shown in c, it was found that... m- The herringbone channels in the KN-GO membrane are blocked, and only the zigzag channels exist.

[0122] right m XRD characterization of the -KN-GO (3:1) two-dimensional film was performed, such as Figure 7 As shown in d.

[0123] Comparative Example 3 This comparative example provides a... m- KN-PSS membrane, by adjusting m- KN (prepared in Example 1) and PSS were prepared by different mass ratios. m- KN-PSS two-dimensional membrane. The preparation steps are basically the same as in Example 3. The KN-PSS membrane prepared in Example 1 was used... m -KN and PSS (M w =80k, AR, Sigma-Aldrich Co. Ltd.) Figure 8 After mixing at different mass ratios as shown in figure a, vacuum filtration was performed to obtain various... m- The thickness of the KN-PSS two-dimensional membrane is 1 μm.

[0124] The method for determining the permeation rate of a unicomponent system was used for testing. m- KN and PSS with different mass ratios m- KN-PSS two-dimensional membrane K + and Na + The permeation rate and K were calculated. + / Na + The selectivity, such as Figure 8 As shown in Figure a, it can be seen that as the amount of sodium polystyrene sulfonate inserted increases, m The alkali metal ion selectivity of the -KN-PSS two-dimensional membrane also gradually decreased, indicating that sodium polystyrene sulfonate disrupted the alkali metal ion selectivity. m- The interlayer channels of the KN film also demonstrate the important role of channel ordering. This was obtained using SEM.m- KN-PSS two-dimensional membrane ( m SEM cross-sectional image of (KN / PSS mass ratio of 1:3) is shown below. Figure 8 As shown in b, it can be seen from the figure that m- Although the cross-section of the KN-PSS (1:3) two-dimensional membrane still maintains a compact structure, it does not exhibit... Figure 5 The structure shown in b is not a clearly two-dimensional film stacking structure, but a dense structure close to that of a polymer film, indicating that the insertion of sodium polystyrene sulfonate disrupts the interlayer channels.

[0125] Test Example 1-1 This test example is for determining the permeation rate of a unary system, used to measure the permeation rate of the system prepared in Example 2. m- KN two-dimensional film (approximately 1 μm thick), prepared in Example 3 m- KN-GO two-dimensional membrane and Comparative Example 2 prepared p- KN two-dimensional membranes are effective against different metal ions (Li). + , K + Al 3+ Mg 2+ Na + Ca 2+ Ba 2+ The permeation rates of the unicomponent system are as follows: Figure 9 As shown in ac.

[0126] for m- The KN two-dimensional membrane (Example 2) has an average permeability of 0.002-0.02 mol·m⁻¹ for most ions. –2 ·h –1 ( Figure 9 a). However, Li + and K + It exhibited rapid permeation, reaching 2.02 and 2.85 mol·m⁻¹, respectively. –2 ·h –1 Compared to other cations (Al) 3+ Mg 2+ Na + Ca 2+ ,Ba 2+ ) is 1-2 orders of magnitude higher (of which Na) + The permeability is 0.054 mol·m –2 ·h –1 ), approaching 88% of free diffusion. + / Na + and K + / Na +The selectivity reached 37.4 and 52.8 respectively, which is far higher than the selectivity reported in existing technologies and exceeds the latest record of alkali metal separation membranes.

[0127] In contrast. p -KN membrane (Comparative Example 2) permeability for different metal ions, such as Figure 9 As shown in c, Li + / Na + and K + / Na + The selectivity decreased to 3.3 and 1.7, respectively. Therefore, the highly ordered ion channels in this invention... m -KN two-dimensional films exhibit unusual Li content compared to other cations. + or K + Selectivity.

[0128] and m- The results of the permeation rate determination of the KN-GO (3:1) two-dimensional membrane monolithic system are as follows: Figure 9 As shown in b, consistent with the theoretical derivation in Example 3, it exhibits a high Li... + / K + and Li + / Na + The selectivity.

[0129] We after penetration testing m -KN film was characterized by XRD, such as Figure 5 As shown in d, the ion transport pathways within the membrane are analyzed.

[0130] In the preparation m In the KN film, the diffraction between the (020), (040), and (120) crystal planes is located in the 3-5°, 7-10.5°, and 11.6-14° regions, respectively. Figure 5 d). As an indicator of the spacing between the two NbO6 octahedral layers, two (040) peaks appear at 8.59° and 8.94° (labeled as (040) respectively). H and (040) Z ), respectively corresponding to m -KN layers combine herringbone and zigzag patterns. After Na... + After the permeation test, due to Na + Almost failed m- KN membrane, m- The XRD peaks of the KN film remained almost unchanged; while those of the Li film remained almost unchanged. + or K + After the penetration test, (040) Z The peak remains at 8.90°, while (040) HThe peak part (green) is shifted to 8.22°, indicating the expansion of the herringbone channel and that Li + or K + both preferentially pass through the herringbone channel.

[0131] For the m- KN-GO two-dimensional membrane after the penetration test, XRD characterization was carried out, as Figure 7 shown in d, to analyze the ion transport path within the membrane.

[0132] As can be seen from Figure 7 d, after the alkali metal ion penetration test, the characteristics of the channel structure change. Specifically, before the penetration test, the (040) m peak of the -KN-GO membrane is located at 8.94° (corresponding to the zigzag channel), while the (040) Z peak has basically disappeared or its intensity has significantly decreased, indicating that the herringbone channel has been effectively blocked by GO and does not participate in ion transport. After the Na H or K + penetration test, the position of the (040) + peak hardly changes and there is no obvious expansion of the channel; however, after the Li Z penetration test, the (040) + peak is partially shifted to about 8.22°, indicating the expansion of the zigzag channel and that Li Z preferentially passes through the zigzag channel. This shows that in the prepared + -KN-GO membrane, the insertion of GO causes the herringbone channel to be blocked and ion transport mainly occurs through the zigzag channel. m The K

[0133] The penetration rates of K Figure 9 and Li m- in the KN two-dimensional membrane (prepared in Example 2, with a thickness of 1 μm) in a were compared with the penetration rates of K + [[ID= 、Li + and Li + in nylon, Mg-Al LDH, MXene, GO, and Vermiculite two-dimensional membranes in the prior art. All the two-dimensional membranes use a nylon substrate (pore size: 0.22 μm, Jinteng Company), as + shown in, Figure 10 The penetration rates of the KN two-dimensional membrane for K m- and Li + and Li + exceed most of the two-dimensional membranes in the prior art.

[0134] Test Example 1-2 This test example is for the determination of the binary system separation ratio.

[0135] To evaluate the separation factor of alkali metal ions, the separation performance of the membrane in a binary system was further determined by separating a mixture of binary alkali metal ions.

[0136] This test case examined three separate two-dimensional membranes. Evaluation was performed using ion chromatography at room temperature. m -KN (Example 2, thickness 1 μm) and m- The separation performance of the KN-GO membrane (Example 3, 3:1, thickness 1 μm) in the binary system is shown in Table 1.

[0137] Table 1. Room temperature m -KN and m- Separation performance of KN-GO membrane in binary systems (permeability unit: mol·m⁻¹) –2 ·h –1 )

[0138] As can be seen from the data in Table 1, K + / Na + In a binary system m -KN membrane Na + The average permeability is 0.0243 mol·m⁻². –2 ·h –1 K + The average permeability is 1.1133 mol·m⁻². –2 ·h –1 K + / Na + The separation ratio was 45.8.

[0139] Li + / Na + In a binary system m -KN membrane Na + The average permeability is 0.029 mol·m⁻². –2 ·h –1 Li + The average permeability is 0.96 mol·m –2 ·h –1 Li + / Na + The separation ratio was 33.1.

[0140] Li + / K + In a binary system m -KN-GO membrane K + The average permeability is 0.0313 mol·m⁻². –2 ·h –1 Li +The average permeability is 0.87 mol·m –2 ·h –1 Li + / K + The separation ratio was 27.8.

[0141] Evaluation by ion chromatography at room temperature m -KN (Example 2, thickness 1μm) and m- The stability of the separation performance of the KN-GO membrane (Example 3, 3:1, thickness 1 μm) in the binary system is as follows: Figure 11 As shown.

[0142] Test Example 1-3 This test example demonstrates the determination of lithium-ion separation in a ternary system.

[0143] Previous work has not reported the successful separation of ternary mixtures containing monovalent alkali metal ions. Based on the successful separation of binary alkali metal ion mixtures described above, we propose a method for sodium-retaining... m- KN membrane and lithium permeable m- The KN-GO membrane sequentially combines three... m- KN film (Example 2, thickness 1 μm) and 2 m- KN-GO membranes (Example 3, 3:1, 1 μm thickness) were connected in series, allowing a ternary mixed ion of sodium, potassium, and lithium to pass sequentially through the five two-dimensional membranes, resulting in the following... Figure 12 The graph shows the abundance trend of lithium ions.

[0144] As can be seen from the diagram, after three layers... m After selective separation by the KN membrane, the lithium-ion abundance increased from 33.3% to 68.9%. Subsequently, through two additional layers... m- KN-GO membrane separation further increased the lithium-ion abundance to 91.1%.

[0145] Test Example 2 This test case is... m- Stability testing of KN two-dimensional membranes.

[0146] To evaluate the stability of the membrane, the membrane prepared in Example 2 was used. m- When a KN two-dimensional membrane (1 μm thick) was placed in water for 24 hours, no cracks or expansion were observed, indicating that it has good anti-expansion properties. m- The PXRD diffraction patterns of the KN two-dimensional membrane before and after continuous immersion in liquid water for 24 hours are shown below. Figure 13 As shown in Figure a, the peak positions before and after soaking show only slight differences, indicating that the product prepared in Example 1... m- The KN membrane exhibits good stability. In contrast, the membrane prepared in Comparative Example 1... p-KN two-dimensional membranes can be immediately disintegrated and completely collapsed upon contact with deionized water. p- PXRD diffraction patterns of the KN membrane before and after continuous immersion in liquid water for 24 hours are shown below. Figure 13 As shown in b, this indicates that the (020), (040), and (120) diffraction peaks disappeared or decreased after soaking, indicating that... p- KN membranes have poor stability. Therefore, based on the above comparison, m- KN membranes exhibit better stability as separation membranes.

[0147] In summary, this invention utilizes a niobate two-dimensional membrane to separate Li + Na + or K + .for m -KN membrane, as shown in Table 1, K + / Na + and Li + / Na + The separation factors in the binary mixture reached 45.8±4 and 33.1±2, respectively, and can be used to retain or remove Na. + .

[0148] for m- KN-GO membrane ( m -KN to GO mass ratio is 3:1), as shown in Table 1, Li + / K + The separation factor is as high as 27.8±3, suitable for the retention or removal of potassium ions or the enrichment of lithium ions. It is worth noting that most current reports give the ideal selective permeability by calculating the ratio of alkali metal ion permeation rates, while in this invention, the separation factor is directly determined using a binary mixture, providing a more valuable reference for practical applications. The above-mentioned separation factor fluctuates by less than 20% over 12 hours (e.g., Figure 11 As shown in the figure, it exhibits excellent stability.

[0149] Furthermore, the ion permeability of the niobate two-dimensional membrane of the present invention is 3-10 times higher than that of two-dimensional material-based membranes reported in the prior art, such as... Figure 10 As shown, this is close to the level of ion diffusion through the nylon substrate in the bulk solution.

[0150] based on m -KN and m- The ion selectivity of KN-GO membranes is above 25. We used two membranes in series to purify lithium ions and explored their application potential in more complex ternary systems. Figure 12 As shown, after three layers m -KN membrane and two layers m-KN-GO membrane separation increased lithium-ion abundance to 91.1%, exceeding industrial-grade levels. Based on these results, the niobate two-dimensional membrane and its composite membrane provided by this invention exhibit significantly higher alkali metal ion separation performance than existing technologies.

[0151] The above description provides an illustrative overview of the present invention and its embodiments. This description is not restrictive, and the embodiments shown are merely one example of the invention's implementation. Actual implementations are not limited to these examples. Therefore, if those skilled in the art are inspired by this description and design similar implementations and examples without departing from the spirit of the invention, such designs should fall within the scope of protection of the present invention.

Claims

1. Niobate / graphene oxide composite nanosheets, wherein the composite nanosheets comprise niobate nanosheets and graphene oxide nanosheets; In the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 5 nm and the maximum lateral dimension of the niobate nanosheets is greater than or equal to 100 nm. In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1.5 nm and the maximum lateral dimension of the graphene oxide nanosheets is greater than or equal to 100 nm.

2. The niobate / graphene oxide composite nanosheet according to claim 1, characterized in that: In the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 3 nm and the maximum lateral dimension of the niobate nanosheets is greater than or equal to 100 nm. In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1 nm and the maximum lateral dimension of the graphene oxide nanosheets is greater than or equal to 100 nm.

3. The niobate / graphene oxide composite nanosheet according to claim 1 or 2, characterized in that: The niobium content in the composite nanosheets ranges from 16.15% to 50.13% by mass.

4. Niobate / graphene oxide composite nanosheets, wherein the composite nanosheets comprise niobate nanosheets and graphene oxide nanosheets; The mass ratio of the niobate nanosheets to the graphene oxide nanosheets is (0.4-4.5):

1.

5. The niobate / graphene oxide composite nanosheet according to claim 4, characterized in that, In the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 5 nm and the maximum lateral dimension of the niobate nanosheets is greater than or equal to 100 nm. In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1.5 nm and the maximum lateral dimension of the graphene oxide nanosheets is greater than or equal to 100 nm.

6. A dispersion containing the niobate / graphene oxide composite nanosheets according to any one of claims 1 to 5, wherein the dispersion medium of the dispersion contains water; and the mass concentration of the dispersed phase in the dispersion is 0.01 to 100 mg / mL.

7. A method for preparing a dispersion of niobate / graphene oxide composite nanosheets according to any one of claims 1 to 5, or according to claim 6, characterized in that... Includes the following steps: A dispersion containing niobate nanosheets and a dispersion containing graphene oxide nanosheets were mixed. The mass concentration of niobate nanosheets in the dispersion containing niobate nanosheets is 0.01~100 mg / mL; The mass concentration of graphene oxide nanosheets in the dispersion containing graphene oxide nanosheets is 0.01~100 mg / mL; The method for preparing the dispersion of niobate nanosheets includes the following steps: Soaking steps: Add M4Nb6O 17 The crystals are immersed in an acidic solution to obtain an acidic dispersion; M is selected from K, Na, or Li; Intercalation step: The acidic dispersion is subjected to hydrothermal intercalation to obtain an intercalated dispersion; Microfluidization step: The intercalated dispersion is microfluidized using a microfluidic jet injector to obtain a microfluidized dispersion; Centrifugation step: The microfluidic dispersion is centrifuged to obtain a dispersion of niobate nanosheets.

8. The preparation method according to claim 7, characterized in that: In the microfluidization step, the pressure of the microfluidic ejector is 500~2000 bar, and the microfluidization time is 0.5~10 h.

9. A niobate / graphene oxide composite two-dimensional film, wherein the composite two-dimensional film comprises niobate nanosheets and graphene oxide nanosheets; More than 80% of the niobate nanosheets and graphene oxide nanosheets have a maximum lateral dimension greater than or equal to 100 nm; In the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 5 nm; In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1.5 nm; The thickness of the composite two-dimensional film is 0.05~10 μm.

10. The niobate / graphene oxide composite two-dimensional film according to claim 9, wherein more than 80% of the niobate nanosheets have a thickness of less than 3 nm; In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1 nm.

11. The niobate / graphene oxide composite two-dimensional membrane according to claim 10, wherein the mass percentage of niobium in the composite two-dimensional membrane is 16.15% to 50.13%.

12. A niobate / graphene oxide composite two-dimensional film, wherein the composite two-dimensional film comprises niobate nanosheets and graphene oxide nanosheets; the mass ratio of the niobate nanosheets to the graphene oxide nanosheets is (0.4-4.5):1; More than 80% of the niobate nanosheets and graphene oxide nanosheets have a maximum lateral dimension greater than or equal to 100 nm; In the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 5 nm; In the graphene oxide nanosheets, more than 80% of the graphene oxide nanosheets have a thickness of less than 1.5 nm; The thickness of the composite two-dimensional film is 0.05~10 μm.

13. The niobate / graphene oxide composite two-dimensional film according to claim 12, characterized in that: The Li in the niobate / graphene oxide composite two-dimensional film + / K + The separation ratio is greater than 5.

14. The application of the niobate / graphene oxide composite two-dimensional membrane according to any one of claims 9 to 13 in the separation of alkali metal ions; wherein the alkali metal ion is Li + The application is from Li + Separating Li from the system + Preferably, the one containing Li + The system is selected from one of the following systems: K + / Li + Na + / Li + Or Na + / K + / Li + .

15. A two-dimensional membrane assembly device, the two-dimensional membrane assembly device comprising a niobate two-dimensional membrane and a niobate / graphene oxide composite two-dimensional membrane connected in series; The niobate two-dimensional film comprises niobate nanosheets; In the niobate nanosheets, more than 80% of the niobate nanosheets have a thickness of less than 5 nm and the maximum lateral dimension of the niobate nanosheets is greater than or equal to 100 nm. The thickness of the niobate two-dimensional film is 0.05~10 μm; Hermann orientation factor of the niobate two-dimensional film f Not less than 0.9; The niobate / graphene oxide composite two-dimensional film is the niobate / graphene oxide composite two-dimensional film according to any one of claims 9 to 13.

16. The two-dimensional membrane assembly device according to claim 15, wherein the number of niobate two-dimensional membranes in the two-dimensional membrane assembly device is one or more; wherein the number of niobate / graphene oxide composite two-dimensional membranes in the two-dimensional membrane assembly device is one or more.

17. The application of the two-dimensional membrane assembly device according to claim 15 or 16 in the separation of alkali metal ions; wherein the alkali metal ion is Li + The application is from Li + Separating Li from the system + Preferably, the one containing Li + The system is selected from one of the following systems: Na + / Li + K + / Li + Or Na + / K + / Li + .

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