A method for preparing high-quality oxide nanosheets and thin films based on a liquid-phase exfoliation method

Abstract

This invention relates to two-dimensional material preparation technology, specifically to a method for preparing high-quality oxide nanosheets and thin films based on liquid-phase exfoliation. The method involves synthesizing a layered precursor through a solid-phase reaction, followed by ion exchange using a protic acid to replace interlayer metal ions with hydrogen ions, thereby weakening the interlayer forces. Then, efficient and low-defect liquid-phase exfoliation is achieved through gentle mechanical oscillation with an organic base, yielding a single-layer or few-layer oxide nanosheet dispersion. Film formation is then achieved using two different methods: spin coating and layer-by-layer self-assembly. In summary, this invention avoids the damage to the material structure caused by traditional ultrasonic exfoliation and the harm to the human body caused by the use of highly toxic organic solvents. Furthermore, the process is simple, and the method for preparing two-dimensional oxide nanosheets and thin films has a certain degree of universality. The film formation is controllable, and the prepared thin films can be applied to fields such as memristors and optoelectronic devices.

Description

Technical Field

[0001] This invention relates to two-dimensional material preparation technology, specifically to a method for preparing high-quality oxide nanosheets and films based on liquid phase exfoliation. Background Technology

[0002] Two-dimensional materials, due to their unique physicochemical properties such as high specific surface area, quantum confinement effect, excellent band structure, and surface properties, have broad application prospects in optoelectronics and micro / nanoelectronics. Two-dimensional oxide nanosheets have attracted much attention due to their rich composition, layered precursor structure, and stability.

[0003] Layered niobates, as an important class of functional materials, possess a well-defined layered crystal structure (such as the Dion-Jacobson phase or the Ruddlesden-Popper phase), with exchangeable metal ions between their layers. Through exfoliation, monolayer or few-layer nanosheets can be obtained. These nanosheets retain their intrinsic ferroelectric / piezoelectric properties, maintaining room-temperature ferroelectricity even after being exfoliated to a single atomic layer thickness—a characteristic not found in many two-dimensional materials. Furthermore, their large specific surface area and exchangeable interlayer ions provide possibilities for ion intercalation or modification.

[0004] In existing technologies, the exfoliation of layered niobates typically employs an acid exchange combined with organic amine intercalation. However, these methods often require the use of highly toxic organic solvents such as N-methylpyrrolidone (NMP) and N,N-dimethylformamide (DMF), or rely on ultrasonic treatment to assist exfoliation, resulting in poor environmental friendliness, complex operation, and high equipment requirements. Furthermore, for specific compositions of Dion-Jacobson phase niobates KCa2NaNb4O... 13 There are no reports of using gentle mechanical oscillations to achieve efficient stripping. Summary of the Invention

[0005] The purpose of this invention is to provide a method for treating KCa2NaNb4O 13 An environmentally friendly and simple method for preparing oxide nanosheets and thin films is proposed. Through stepwise synergistic chemical-physical exfoliation, the use of toxic organic solvents in traditional methods is avoided, while overcoming the environmental hazards and process defects caused by strong ultrasonic treatment. On this basis, through a multi-path controllable thin film assembly process, the controllable construction from layered precursors to high-performance thin films is realized, providing a material basis and technical support for high-performance thin film devices.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing high-quality oxide nanosheets based on liquid phase exfoliation includes the following steps:

[0008] S1. Provide a layered niobate precursor, said precursor being a Dion-Jacobson phase niobate;

[0009] S2. The layered niobate precursor described in step S1 is brought into contact with a protic acid solution to carry out an ion exchange reaction, so that the interlayer metal ions are replaced by hydrogen ions to obtain protonated layered niobate.

[0010] S3. The protonated layered niobate and tetraalkylammonium hydroxide obtained in step S2 are mixed with water, the pH is adjusted to 9-11, and then the mixture is subjected to mechanical vibration for 3-15 days to achieve interlayer exfoliation and obtain a high-quality oxide nanosheet dispersion.

[0011] In step S3, ultrasonic treatment is not used, and N-methylpyrrolidone or N,N-dimethylformamide is not used in the method.

[0012] Furthermore, the general formula of the Dion-Jacobson phase niobate is A[A'2MnO]. 3n ₊1], where A is an alkali metal ion, A' is an alkaline earth metal ion, M is Nb or a combination of Nb and Ti, and n is an integer from 2 to 5.

[0013] Furthermore, the Dion-Jacobson phase niobate is KCa2NaNb4O 13 or KCa2Nb3O 10 .

[0014] Furthermore, the alkyl group in the tetraalkylammonium hydroxide is a C1 to C4 alkyl group, selected from at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0015] Furthermore, the protic acid mentioned in step S2 is at least one of hydrochloric acid, nitric acid, or sulfuric acid, and the ion exchange reaction is carried out at room temperature for 48 to 96 hours to ensure that the interlayer K⁺ ions are fully replaced.

[0016] Furthermore, the mechanical oscillation described in step S3 is carried out in a constant temperature oscillator at a temperature of 20–30°C to ensure the stability of the reaction system and the stripping efficiency; the oscillation frequency is 100–300 rpm.

[0017] Furthermore, after step S3, the process includes centrifuging the obtained dispersion at a speed of 2000–4000 rpm for 10–30 minutes, collecting the supernatant to obtain a purified nanosheet dispersion, thereby removing incompletely detached particles.

[0018] A method for preparing high-quality oxide nanosheet thin films based on liquid phase exfoliation, characterized by comprising the following steps:

[0019] High-quality oxide nanosheet dispersions were prepared using the above method, and then film was formed on the substrate by spin coating, dip coating or layer-by-layer self-assembly.

[0020] Furthermore, the spin coating method includes: dropping a nanosheet dispersion onto a rotating substrate, first spreading it by rotating at a low speed of 50-300 rpm for 5-30 seconds, then forming a thin film by rotating at a high speed of 1000-6000 rpm for 20-180 seconds, and then heat-treating it at 50-200°C for 1-60 minutes.

[0021] The layer-by-layer self-assembly method includes: (1) hydrophilizing the substrate; (2) immersing the substrate in a cationic polyelectrolyte solution for 5-30 minutes to adsorb onto the substrate surface, making the substrate surface positively charged; (3) immersing the substrate in a nanosheet dispersion for 5-30 minutes to adsorb onto the substrate surface through electrostatic attraction; and (4) repeating steps (2) and (3) 1-10 times to obtain a multilayer nanosheet film. The cationic polyelectrolyte is preferably polydimethyldiallylammonium chloride or polyethyleneimine.

[0022] A method for preparing high-quality oxide nanosheet films based on liquid phase exfoliation is provided, which is prepared by the above-mentioned method for preparing high-quality oxide nanosheet films.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. Environmental friendliness: The method of this invention uses water as the only dispersion medium and does not use highly toxic organic solvents such as N-methylpyrrolidone and N,N-dimethylformamide throughout the process. The process is green and environmentally friendly and meets the requirements of sustainable development.

[0025] 2. Simple process: This invention uses conventional ion exchange combined with constant temperature mechanical oscillation to achieve stripping, which does not require complex equipment, is easy to operate, and is easy to scale up for production.

[0026] 3. Controllable film formation: The spin coating method and layer-by-layer self-assembly method provided by this invention can achieve uniform spreading of nanosheets on the substrate, and the resulting film thickness is controllable and the surface is smooth, which is suitable for a variety of substrate materials. Attached Figure Description

[0027] Figure 1 A schematic diagram of the process for preparing oxide nanosheets by liquid phase exfoliation.

[0028] Figure 2 Schematic diagram of the process for preparing nanosheet thin films by electrostatic layer-by-layer self-assembly

[0029] Figure 3 Schematic diagram of the process for preparing nanosheet thin films by spin coating.

[0030] Figure 4 This is a schematic diagram of a layered oxide precursor.

[0031] Figure 5 A schematic diagram of the proton exchange process of layered oxide precursors;

[0032] Figure 6 A schematic diagram illustrating the principle of TBAOH-assisted liquid-phase exfoliation of layered oxide precursors;

[0033] Figure 7 A schematic diagram illustrating the principle of thin film fabrication through electrostatic layer-by-layer self-assembly.

[0034] Figure 8 This is a schematic diagram of the spin coating film formation process;

[0035] Figure 9 shows the XRD patterns of related materials in the preparation process of calcium, sodium, niobium, and oxygen nanosheets, where (a) is KCa2NaNb4O 13 (b) is the product obtained by acid exchange: HCa2NaNb4O 13 • 1.5H2O;

[0036] Figure 10 The UV-Vis absorption spectrum of calcium, sodium, niobium, and oxygen nanosheets;

[0037] Figure 11 The AFM results for calcium, sodium, niobium, and oxygen nanosheets are shown, where (a) is the morphology of the calcium, sodium, niobium, and oxygen nanosheets, and (b) is the thickness analysis of the corresponding calcium, sodium, niobium, and oxygen nanosheets.

[0038] Figure 12 SEM results of niobic acid (calcium sodium niobium oxide nanosheet precursor) at different magnifications; (a) Result image at 20,000x magnification (b) Result image at 25,000x magnification;

[0039] Figure 13 SEM results of calcium sodium niobium oxide nanosheet films prepared by spin coating at different magnifications; (a) 20,000x magnification and (b) 10,000x magnification.

[0040] Figure 14 SEM results of calcium-sodium-niobium-oxygen nanosheet films prepared by electrostatic layer-by-layer self-assembly at different magnifications: (a) 10,000x magnification and (b) 20,000x magnification. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0042] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0043] Example 1: Preparation of high-quality oxide nanosheets. In this example, the high-quality oxide nanosheets are calcium-sodium-niobium-oxygen nanosheets, and the preparation process is as follows: Figure 1 As shown.

[0044] Step 1: Layered precursor KCa2NaNb4O 13 The solid-phase synthesis, the specific process is as follows: Figure 2 As shown.

[0045] 1) Raw material preparation: Analytical grade (≥99.0%) K₂CO₃, CaCO₃, Na₂CO₃, and Nb₂O₅ powders were used as starting materials. To prevent errors caused by moisture absorption, all raw materials were dried in a 120℃ drying oven for 2 hours before use. The target product is KCa₂NaNb₄O₅. 13 The stoichiometric ratios were determined, and each raw material was accurately weighed using a precision analytical balance.

[0046] 2) Synthesis intermediate KCa2Nb3O 10 :

[0047] Weighed K₂CO₃, CaCO₃, and Nb₂O₅ were ground in an agate mortar for 30 minutes. The mixture was then transferred to a corundum crucible and sintered in a muffle furnace under air atmosphere at a rate of 5°C / min to 1000°C for 10 hours. After cooling in the furnace, the mixture was ground into a fine powder for later use. The purpose of this 1000°C high-temperature solid-state reaction process is to ensure complete reaction of all components, forming well-crystallized layered potassium calcium niobate (KCa₂Nb₃O₅). 10 )Mutually.

[0048] 3) Synthesis of intermediate NaNbO3: Weigh Na2CO3 and Nb2O5 according to the stoichiometric ratio, and sinter them at 1000℃ for 10 hours using the same method as in step 2) of step one to synthesize sodium niobate (NaNbO3) powder with perovskite structure. After calcination, grind it for later use.

[0049] 4) Synthesis of the target precursor KCa2NaNb4O 13 The KCa2Nb3O prepared in step 2) of step one. 10 The powder was precisely mixed with the NaNbO3 powder obtained in step 3) of step one at a molar ratio of 1:1. After thorough wet grinding and drying, the uniformly mixed powder was placed in a muffle furnace and calcined at 1200°C at a rate of 5°C / min in air atmosphere for 24 hours. After natural cooling, it was ground to obtain the product. This high-temperature and long-term calcination can promote solid-phase diffusion and structural reorganization of the two intermediates, ultimately forming a Dion-Jacobson phase KCa2NaNb4O with a well-defined layered structure. 13 Its crystal structure and purity were confirmed by XRD.

[0050] Step 2: Proton exchange reaction

[0051] 1) Acid exchange treatment: Take an appropriate amount of KCa2NaNb4O synthesized in step one 13 The powder was immersed in a 5 mol / L nitric acid solution, with the acid volume ensuring complete immersion and excess of the powder, and the solid-liquid ratio controlled between 1:100 and 1:200. The resulting mixture was then placed in a polytetrafluoroethylene container and magnetically stirred at 200-300 rpm for 72 hours at room temperature to ensure complete and uniform replacement of interlayer potassium ions with hydrogen ions. The reaction process is as follows: Figure 2 and Figure 3 As shown, after the reaction was completed, a high-speed centrifuge with a speed of 10,000 rpm was used for 5 minutes to separate the solid and liquid components, and the acidic supernatant containing exchange products such as potassium nitrate was discarded.

[0052] 2) Washing and drying: Add a large amount of deionized water to the precipitate, then repeatedly centrifuge and wash 5-8 times until the pH of the supernatant is close to neutral (6.5-7.5), thoroughly removing residual acid and ionic byproducts. The resulting white precipitate is protonated niobate HCa₂NaNb₄O. 13 The nH2O was dried overnight in a vacuum drying oven at 60℃ to obtain a loose protonated precursor powder. The bound water content was determined to be approximately 1.5H2O by thermogravimetric analysis.

[0053] Step 3: Mild liquid-phase stripping assisted by organic base

[0054] 1) Preparation of the stripping system: Weigh 100 mg of dry protonated niobate HCa2NaNb4O 13• 1,5H₂O was dispersed in 50 mL of ultrapure deionized water and ultrasonically dispersed for 5 minutes to form a preliminary suspension. Under continuous gentle stirring, a 0.1 mol / L tetrabutylammonium hydroxide (TBAOH) aqueous solution was added dropwise, and the pH of the suspension was precisely adjusted to 10.0 ± 0.2 using a pH meter for real-time monitoring. The amount of BAOH added is typically approximately 2-5 mL per 100 mg of protonated niobate.

[0055] 2) Isothermal Oscillating Peeling: In step 3, the final product from step 1) is transferred to a stoppered conical flask or polypropylene tube and placed in an isothermal oscillating incubator. The temperature is set at 25°C and the oscillation frequency at 200 rpm for continuous mechanical oscillation for 7 days. This process completely avoids the use of any ultrasonic treatment.

[0056] Under the isothermal oscillation conditions of this embodiment, the TBA⁺ large cations gradually embed and expand the weakened interlayer, and combined with the shear force generated by continuous oscillation, the layered structure achieves gradual expansion and eventual dissociation. The entire glass process is described in [reference needed]. Figure 4 .

[0057] Step 4: Purification and Collection of Nanosheet Dispersion

[0058] 1) Separation and Purification: After shaking for 7 days, the dispersion was removed. At this point, the system changed from turbid to translucent or exhibited an opalescent Tyndall effect, indicating that the nanosheets had formed a colloidal dispersion. To remove incompletely peeled thick particles, a small amount of unreacted clumps, and possible agglomerates, the nanosheets were centrifuged at 3000 rpm for 20 minutes. This operation caused thicker and larger particles to precipitate, while single-layer and few-layer nanosheets were retained in the supernatant.

[0059] 2) Product Acquisition: Carefully collect the pale milky white supernatant exhibiting a clear Tyndall effect; this is a high-quality colloidal aqueous dispersion of calcium, sodium, niobium, and oxygen nanosheets, primarily composed of monolayers. For example... Figure 10 As shown, quantitative determination was performed using a UV-Vis spectrophotometer combined with the standard curve method. The final concentration of the dispersion obtained in step 1 of step four was approximately 0.1 mg / mL. The dispersion was stable at 4°C for several weeks. The SEM results of the obtained calcium-sodium-niobium-oxygen nanosheet precursor will be... Figure 10 .

[0060] Example 2: Preparation of calcium, sodium, niobium, and oxygen nanosheet films by spin coating

[0061] like Figure 3As shown, the aqueous dispersion of calcium, sodium, niobium, and oxygen nanosheets prepared in Example 1 was centrifuged at 10,000 rpm for 15 minutes. The nanosheet precipitate was collected, and the supernatant was discarded. The precipitate was redispersed in dimethyl sulfoxide (DMSO). DMSO has a high boiling point, moderate surface tension, and good wettability, which can suppress the coffee ring effect caused by uneven evaporation rates of pure water, thus facilitating the formation of a smooth and uniform film. The nanosheet concentration was adjusted to approximately 1 mg / mL, and brief, gentle shaking was used to ensure uniform dispersion.

[0062] A clean silicon wafer substrate was fixed onto the vacuum chuck of a spin coater. Using a micropipette, 100 μL of a nanosheet-dimethyl sulfoxide dispersion was dropped onto the center of the stationary substrate. The spin coater was started, initially rotating at 100 rpm for 10 seconds to allow the dispersion to spread thoroughly on the substrate surface; then, it was rotated at 3000 rpm for 60 seconds to utilize centrifugal force to evenly distribute the nanosheets and rapidly dry them into a film. After spin coating, the substrate was transferred to a 100°C hot plate for heat treatment for 10 minutes to remove residual solvent and enhance the adhesion between the nanosheets and the substrate, resulting in a uniform and dense calcium-sodium-niobium-oxygen nanosheet film.

[0063] Example 3: Preparation of calcium, sodium, niobium, and oxygen nanosheet films by layer-by-layer self-assembly

[0064] like Figure 2 As shown, the silicon wafer substrate is ultrasonically cleaned sequentially with acetone, ethanol and deionized water to remove organic impurities and particulate contaminants from the surface. Then it is placed in an oxygen plasma cleaner for 10 minutes to further clean the substrate surface and introduce hydrophilic functional groups such as hydroxyl groups, thereby improving the surface hydrophilicity and surface energy and providing a basis for subsequent electrostatic assembly.

[0065] A 1 mg / mL aqueous solution of polydimethyldiallyl ammonium chloride (PDMC) was prepared. PDMC is a strong cationic polyelectrolyte that becomes positively charged after ionization in water. The plasma-treated substrate was immersed in the PDMC aqueous solution and allowed to stand for 20 minutes to allow the positively charged polyelectrolyte to firmly adsorb onto the negatively charged substrate surface via electrostatic attraction, forming a uniform positively charged modification layer. After removal, the substrate was rinsed with deionized water for 30 seconds to remove unbound molecules from the physical adsorption process, and then dried with nitrogen gas.

[0066] The modified substrate was immersed in the aqueous dispersion of calcium, sodium, niobium, and oxygen nanosheets prepared in Example 1. The dispersion concentration was diluted to approximately 0.1 mg / mL. The nanosheets carried a negative charge on their surface, which allowed them to electrostatically attract the positively charged layer on the substrate surface. After standing for 20 minutes to allow the nanosheets to align parallel to the substrate surface and adhere tightly, the substrate was removed, rinsed with deionized water, and dried with nitrogen.

[0067] The polydiallyl ammonium chloride modification and nanosheet adsorption steps were repeated three times to assemble a multilayer composite structure layer by layer. The assembled film was then placed in a vacuum drying oven at 60°C for 2 hours to remove residual moisture and solvent, enhance interlayer bonding, and release internal stress, ultimately yielding a well-structured, tightly bonded calcium-sodium-niobium-oxygen nanosheet multilayer composite film.

[0068] Figure 4 This is a schematic diagram of a layered precursor. Figure 5 This is a schematic diagram of the proton exchange process. Figure 6 This is a schematic diagram illustrating the principle of the TBAOH-assisted liquid-phase exfoliation mechanism. Figures 4 to 6 As can be seen, the method of this invention uses water as the sole dispersion medium and does not use highly toxic organic solvents such as N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF) throughout the entire process. This process feature avoids the use of toxic solvents, simplifies post-processing steps, reduces environmental risks and operational complexity in the production process, and aligns with the development direction of green chemistry.

[0069] Figure 7 This is a schematic diagram illustrating the principle of electrostatic layer-by-layer self-assembly. Figure 8 This is a schematic diagram of the spin coating film formation process. (From 7 and...) Figure 8 As can be seen, this invention provides two film formation technologies: spin coating and layer-by-layer self-assembly, each suitable for different application needs. Spin coating is simple and efficient, suitable for rapidly preparing large-area uniform films; layer-by-layer self-assembly allows for precise control of film thickness and number of layers, suitable for constructing multilayer structures and complex heterostructures.

[0070] Figure 9 The XRD patterns of related materials in the preparation of calcium, sodium, niobium, and oxygen nanosheets are shown, where (a) is KCa2NaNb4O 13 (b) is the product obtained by acid exchange: HCa2NaNb4O 13 • 1.5H2O; through Figure 9 The XRD results of samples a and b confirm the successful synthesis of the precursor and the formation of the protonated product, indicating that the inventive method is applicable to Dion-Jacobson phase niobates.

[0071] Figure 11 The AFM results for calcium, sodium, niobium, and oxygen nanosheets are shown, where (a) is the morphology of the calcium, sodium, niobium, and oxygen nanosheets, and (b) is the thickness analysis of the corresponding calcium, sodium, niobium, and oxygen nanosheets. Based on... Figure 11 As can be seen from 'a' and 'b', the thickness of the nanosheets obtained by the method of the present invention is about 1.5 nm, corresponding to a single-layer nanosheet.

[0072] Figure 12SEM results of niobic acid (calcium sodium niobium oxide nanosheet precursor) at different magnifications; (a) Result image at 20,000x magnification (b) Result image at 25,000x magnification; Figure 13 SEM results of calcium sodium niobium oxide nanosheet films prepared by spin coating at different magnifications; (a) 20,000x magnification and (b) 10,000x magnification. Figure 14 SEM results of calcium-sodium-niobium-oxygen nanosheet films prepared by electrostatic layer-by-layer self-assembly at different magnifications: (a) 10000x magnification; (b) 20000x magnification. Figure 12 a and b in Figure 13 a and b in the middle and Figure 14 As indicated by a and b in the text, this invention utilizes two film-forming techniques—spin-coating and layer-by-layer self-assembly—to prepare the calcium-sodium-niobium-oxygen nanosheets obtained in Example 1. These techniques produce films with uniform surfaces and dense structures, enabling the exfoliation and film formation of Dion-Jacobson phase niobates, providing a feasible technical solution for the two-dimensionalization of this type of material. The two methods are suitable for different application requirements. Spin-coating is simple and efficient, suitable for the rapid preparation of large-area uniform films; layer-by-layer self-assembly allows for precise control of film thickness and the number of layers, suitable for constructing multilayer structures and complex heterostructures.

[0073] In summary, this invention provides a complete technical solution for the synthesis of Dion-Jacobson phase niobate precursors, proton exchange, liquid-phase exfoliation, and thin film preparation. This solution covers the main steps in the preparation and application of two-dimensional nanosheets, providing an operable technical path for related research and applications (see [link to article]). Figures 1 to 3 Regarding the operability of process parameters, key parameter ranges for the exfoliation process are provided based on the characteristics of Dion-Jacobson phase niobates, including: pH value of the exfoliation system controlled at 9-11; mechanical oscillation time controlled at 3-15 days; oscillation frequency controlled at 50-300 rpm; and alkyl chain length of tetraalkylammonium hydroxide C1-C4. Providing these parameter ranges allows those skilled in the art to adjust the process parameters within these ranges according to specific material types and experimental conditions to obtain stable nanosheet dispersions. For the exfoliation method, mechanical oscillation is used to achieve interlayer exfoliation, avoiding ultrasonic treatment. The continuous shear force provided by mechanical oscillation can gradually achieve interlayer dissociation, and this gentle exfoliation method makes the exfoliation process easier to control. Those skilled in the art can adjust the oscillation frequency and time as needed to adapt to Dion-Jacobson phase niobates with different compositions and numbers of layers.

Claims

1. A method for preparing high-quality oxide nanosheets based on liquid-phase exfoliation, characterized in that, Includes the following steps: S1. Provide a layered niobate precursor, said precursor being a Dion-Jacobson phase niobate; S2. The layered niobate precursor described in step S1 is brought into contact with a protic acid solution to carry out an ion exchange reaction, so that the interlayer metal ions are replaced by hydrogen ions to obtain protonated layered niobate. S3. The protonated layered niobate and tetraalkylammonium hydroxide obtained in step S2 are mixed with water, the pH is adjusted to 9.5-10.5, and then the mixture is subjected to mechanical vibration for 5-10 days to achieve interlayer exfoliation and obtain high-quality oxide nanosheets. In step S3, ultrasonic treatment is not used, and N-methylpyrrolidone or N,N-dimethylformamide is not used in the method.

2. The method according to claim 1, characterized in that, The general formula of the Dion-Jacobson phase niobate is A[A'2MnO]. 3n ₊1], where A is an alkali metal ion, A' is an alkaline earth metal ion, M is Nb or a combination of Nb and Ti, and n is an integer from 2 to 5.

3. The method according to claim 2, characterized in that, The Dion-Jacobson phase niobate is KCa2NaNb4O 13 or KCa2Nb3O 10 .

4. The method according to claim 1, characterized in that, The alkyl group in the tetraalkylammonium hydroxide is a C1 to C4 alkyl group, selected from at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

5. The method according to claim 1, characterized in that, The protic acid mentioned in step S2 is at least one of hydrochloric acid, nitric acid, or sulfuric acid, and the ion exchange reaction is carried out at room temperature for 48 to 96 hours.

6. The method according to claim 1, characterized in that, The mechanical oscillation described in step S3 is carried out in a constant temperature oscillator with an oscillation temperature of 20-30°C and an oscillation frequency of 100-300 rpm.

7. The method according to claim 1, characterized in that, Step S3 is followed by a step of centrifuging the obtained dispersion at a speed of 2000-4000 rpm for 15-30 minutes, and collecting the supernatant to obtain the purified nanosheet dispersion.

8. A method for preparing high-quality oxide nanosheet thin films based on liquid-phase exfoliation, characterized in that, Includes the following steps: A high-quality oxide nanosheet dispersion is prepared by any one of the methods described in claims 1 to 7, and then a film is formed on a substrate by spin coating, dip coating or layer-by-layer self-assembly.

9. The method according to claim 8, characterized in that, The spin coating method includes: dropping a nanosheet dispersion onto a rotating substrate, first spreading it by rotating at a low speed of 50-200 rpm for 5-20 seconds, then forming a thin film by rotating at a high speed of 2000-5000 rpm for 30-120 seconds, and then heat-treating it at 60-120℃ for 5-60 minutes; the layer-by-layer self-assembly method includes: alternately immersing the substrate in a cationic polyelectrolyte solution and a nanosheet dispersion, adsorbing for 5-30 minutes each, and repeating 1-10 times.

10. A method for preparing high-quality oxide nanosheet films based on liquid-phase exfoliation, characterized in that, Prepared by the method according to claim 8 or 9.

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