Large-size monoclinic phase VO2 nanosheet or film as well as preparation method and application thereof

Abstract

The invention provides a large-size monoclinic phase VO2 nanosheet or film and a preparation method and application thereof.The preparation method comprises the steps that VCl3 and V2O3 serve as raw materials, and VOCl single crystals are prepared through a chemical vapor transport method; the method comprises the following steps: tabletting a VOCl single crystal to obtain a VOCl single crystal wafer, and performing electrochemical intercalation stripping in an organic salt electrolyte by taking the VOCl single crystal wafer as a cathode and platinum as a counter electrode to obtain a VOCl single-layer nanosheet; the preparation method comprises the following steps: dispersing VOCl single-layer nanosheets in a polar organic solvent, dripping the obtained solution on a substrate material, and drying; or dripping the obtained solution on an organic filter membrane, carrying out suction filtration to obtain a VOCl thin film, transferring the VOCl thin film to a substrate material, and drying; and carrying out annealing treatment on the VOCl single-layer nanosheet or the VOCl thin film. The thicknesses of the VO2 nanosheet and the thin film can be adjusted, the thinnest thickness can be within 1nm, and the transverse sizes of the VO2 nanosheet and the thin film can be more than tens of microns and 500 microns respectively.

Description

Technical Field

[0001] The invention relates to a large-size monoclinic VO2 nanosheet or film and a preparation method and application thereof, belonging to the technical field of chemical functional materials. Background Art

[0002] VO2 is a type of three-dimensional non-layered material with special phase change properties. When the temperature rises above 68°C, VO2 will transform from the rutile (R) phase with metallic properties to the monoclinic (M) phase with insulating properties. Before and after the phase change, the physical properties such as conductivity and infrared transmittance undergo sudden changes. It can be used in smart windows, sensors, field effect transistors, optical devices, etc.

[0003] At present, the preparation methods of VO2 thin film include physical method and chemical method. Among them, physical methods include pulsed laser deposition and magnetron sputtering, and chemical methods include sol-gel method. In the physical method, pulsed laser deposition is to use pulsed laser to bombard V or V2O5 target to obtain gasified molecules and then cool and deposit them on the substrate to form VO2 thin film. This method has very high requirements on laser parameters and high equipment cost, and the area of ​​the obtained VO2 thin film is small; magnetron sputtering is to use sputtering effect to deposit VO2 thin film on the substrate, usually using argon ions to bombard V or V2O5 target to make V particles or ions escape, and then deposit on the substrate surface to form VO2 thin film after sufficient contact and reaction with oxygen. The VO2 thin film obtained by this method has low purity and often contains other vanadium oxides. Further annealing treatment is required to obtain pure phase VO2 thin film. In the chemical method, sol-gel method is to gel metal organic or inorganic sol, and then obtain VO2 thin film after heat treatment. The experimental process of this method is relatively complicated, the raw materials and reagents are relatively expensive, and the obtained VO2 thin film often has a large number of micropores and low quality. In addition, there are other methods for preparing VO2 thin films, such as chemical vapor deposition and atomic layer deposition, but they all have problems such as complex preparation process and high equipment cost, and cannot be applied on a large scale.

[0004] Preparing VO2 into two-dimensional nanosheets can effectively solve these problems. The use of two-dimensional nanosheets to form films not only simplifies the preparation process, but also reduces the phase transition temperature due to the reduction in film thickness, making the phase transition temperature closer to room temperature and suitable for more different application environments. At present, there are relatively few studies on the preparation of monoclinic VO2 nanosheets in this field. There are two main existing preparation methods. One is the lithiation-stripping method proposed by Xie et al. (Yao, T., Liu, L., Xiao, C., Zhang, X., Liu, Q., Wei, S. and Xie, Y. (2013), Ultrathin Nanosheets of Half-Metallic Monoclinic Vanadium Dioxide with a Thermally Induced Phase Transition. Angew. Chem. Int. Ed., 52: 7554-7558), which chemically lithiates the monoclinic VO2 block in LiCl solution and then performs intercalation and stripping in N, N-dimethylformamide / water to obtain monoclinic VO2 nanosheets; the other is to first prepare metastable VO2 (B) nanosheets or VOOH nanosheets by a hydrothermal method, and then anneal them to obtain monoclinic VO2 nanosheets. However, the above-mentioned lithiation-stripping and hydrothermal-annealing preparation processes are relatively complicated, and the resulting VO2 nanosheets are small in size, less than one micron, and thick.

[0005] Therefore, providing a large-sized monoclinic VO2 nanosheet or VO2 film and a new preparation method and application thereof has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0006] In order to solve the problems of complex preparation process of traditional VO2 nanosheets, large thickness and small size of nanosheets, one object of the present invention is to provide a method for preparing large-sized monoclinic VO2 nanosheets or VO2 films.

[0007] Another object of the present invention is to provide a large-sized monoclinic VO2 nanosheet or a large-sized monoclinic VO2 thin film, which is prepared by the above-mentioned method for preparing the large-sized monoclinic VO2 nanosheet or VO2 thin film.

[0008] Another object of the present invention is to provide the application of the large-sized monoclinic VO2 nanosheets or large-sized monoclinic VO2 films mentioned above in smart windows, sensors, field effect transistors or energy storage devices.

[0009] In order to achieve the above objectives, on the one hand, the present invention provides a method for preparing large-sized monoclinic VO2 nanosheets or VO2 thin films, wherein the preparation method comprises:

[0010] Step 1: Using VCl3 and V2O3 as raw materials, VOCl single crystal is prepared by chemical vapor transport method;

[0011] Step 2: Pressing the VOCl single crystal into a VOCl single crystal, and then using the VOCl single crystal as a cathode and platinum as a counter electrode, electrochemical intercalation and exfoliation in an organic salt electrolyte to obtain a VOCl single-layer nanosheet;

[0012] Step 3: Disperse the VOCl monolayer nanosheets in a polar organic solvent, and then drop the resulting solution onto a substrate material and dry it; or drop the resulting solution onto an organic filter membrane and then filter to obtain a VOCl film, and then transfer the VOCl film onto a substrate material and dry it;

[0013] Step 4: In an inert atmosphere, annealing the VOCl single-layer nanosheet or VOCl film attached to the silicon wafer after drying to obtain a large-sized monoclinic VO2 nanosheet or a large-sized monoclinic VO2 film.

[0014] As a specific implementation of the above preparation method of the present invention, in step 1, the molar ratio of V2O3 to VCl3 is 1:1-10, preferably 1:1.3.

[0015] As a specific embodiment of the preparation method described above, in step 1, the vacuum degree of the chemical vapor transport method is less than 10 -3 mbar, the temperature is controlled at 750-800°C, and the time can be from one to several weeks. For example, in some embodiments of the present invention, the time is 7 days.

[0016] As a specific embodiment of the preparation method described above, in step 2, the organic salt in the organic salt electrolyte includes one or a combination of tetrabutylammonium bromide, tetrahexylammonium bromide and tetra-n-octylammonium bromide.

[0017] As a specific embodiment of the preparation method described above of the present invention, in step 2, the concentration of the organic salt in the organic salt electrolyte is 1-500 mM, preferably 2-10 mM, and more preferably 3 mM.

[0018] As a specific embodiment of the preparation method described above, the solvent used in the organic salt electrolyte includes acetonitrile and the like.

[0019] As a specific embodiment of the preparation method described above, in step 2, the voltage used for electrochemical intercalation stripping is -5 to -10V, preferably -5V.

[0020] The present invention does not make specific requirements for the drying operation and temperature in step 3 of the above-mentioned preparation method, and can be reasonably adjusted according to the actual needs of the on-site operation, as long as the purpose of drying can be achieved.

[0021] As a specific embodiment of the preparation method described above of the present invention, in step three, the polar organic solvent includes N,N-dimethylformamide, isopropanol, dimethyl sulfoxide, N-methylpyrrolidone or propylene carbonate, etc., preferably N,N-dimethylformamide.

[0022] As a specific implementation of the above-mentioned preparation method of the present invention, in step three, the substrate material includes a silicon wafer, a quartz wafer, sapphire or mica, etc., preferably a silicon wafer.

[0023] As a specific implementation of the preparation method described above in the present invention, in step 4, the inert atmosphere includes argon atmosphere, nitrogen atmosphere or hydrogen-argon mixed gas atmosphere.

[0024] As a specific embodiment of the preparation method described above of the present invention, in step 4, the temperature of the annealing treatment is 450-550° C., and the constant temperature time is more than 30 minutes, preferably 0.5-3 hours;

[0025] Also preferably, the annealing treatment temperature is 500° C. and the constant temperature time is 2 h;

[0026] Also preferably, the heating rate during the annealing process is 5-20 K / min, preferably 10 K / min.

[0027] On the other hand, the present invention also provides a large-sized monoclinic VO2 nanosheet or a large-sized monoclinic VO2 thin film, wherein the large-sized monoclinic VO2 nanosheet or the large-sized monoclinic VO2 thin film is prepared by the preparation method of the large-sized monoclinic VO2 nanosheet or VO2 thin film described above.

[0028] As a specific embodiment of the large-sized monoclinic VO2 nanosheets or large-sized monoclinic VO2 films described above in the present invention, the thickness of the large-sized monoclinic VO2 nanosheets and large-sized monoclinic VO2 films are adjustable and the thinnest is less than 1 nm, the lateral size of the large-sized monoclinic VO2 nanosheets can reach tens of μm, preferably 1-50 μm, and the lateral size of the large-sized monoclinic VO2 films is above 500 μm.

[0029] On the other hand, the present invention also provides the use of the large-sized monoclinic VO2 nanosheets or large-sized monoclinic VO2 films described above in smart windows, sensors, field effect transistors or energy storage devices.

[0030] The preparation method of large-size monoclinic VO2 nanosheets or VO2 thin films provided by the present invention is a solution phase preparation method, which first uses VCl3 and V2O3 as raw materials to prepare VOCl single crystals by chemical vapor transport, then obtains VOCl single-layer nanosheets by organic salt-assisted electrochemical intercalation stripping, and finally anneals the VOCl single-layer nanosheets or VOCl thin films in an inert atmosphere to obtain large-size monoclinic VO2 nanosheets or large-size monoclinic VO2 thin films.

[0031] The preparation method of large-sized monoclinic VO2 nanosheets or VO2 films provided by the present invention has a simple process flow, controllable operation / process, and can be used to prepare large-sized monoclinic VO2 nanosheets or VO2 films on a large scale; and the lateral size of the prepared VO2 nanosheets is relatively large, which can reach tens of μm, and the thickness is adjustable and can be as thin as less than 1 nm, with good crystallinity and high purity, and is a monoclinic pure phase; the prepared VO2 film has good continuity, a larger lateral size, which can reach more than 500 μm, and the thickness is adjustable and can be as thin as less than 1 nm, with good crystallinity and high purity, and is a monoclinic pure phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 This is a process flow chart of the method for preparing large-sized monoclinic VO2 nanosheets provided in Example 1 of the present invention.

[0034] Figure 2 This is a process flow chart of the method for preparing a large-sized monoclinic VO2 thin film provided in Example 2 of the present invention.

[0035] Figure 3 This is the Raman scattering spectrum of the large-sized monoclinic VO2 nanosheets prepared in Example 1 of the present invention.

[0036] Figure 4a-4b This is an atomic force microscope image of the large-sized monoclinic VO2 nanosheet prepared in Example 1 of the present invention.

[0037] Figure 5 This is a common optical microscope picture of the large-sized monoclinic VO2 nanosheets prepared in Example 1 of the present invention.

[0038] Figure 6 This is a scanning electron microscope image of the large-sized monoclinic VO2 nanosheets prepared in Example 1 of the present invention.

[0039] Figure 7 This is the Raman scattering spectrum of the large-sized monoclinic VO2 thin film prepared in Example 2 of the present invention.

[0040] Figure 8 This is a common optical microscope picture of the large-sized monoclinic VO2 thin film prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0041] It should be noted that the term "comprises" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0042] "Scope" disclosed in the present invention is given in the form of lower limit and upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges defined in this way are combinable, i.e. any lower limit can be combined with any upper limit to form a range. For example, for a specific parameter, a range of 60-120 and 80-110 is listed, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​listed are 3, 4 and 5, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.

[0043] In the present invention, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in the present invention, and "0-5" is just an abbreviation of these numerical combinations.

[0044] In the present invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in the present invention can be combined with each other to form a new technical solution.

[0045] In the present invention, unless otherwise specified, all technical features and preferred features mentioned in the present invention can be combined with each other to form a new technical solution.

[0046] In the present invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0047] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and Examples. The following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. If the specific conditions are not specified in the embodiments, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0048] Example 1

[0049] This embodiment provides a large-sized monoclinic VO2 nanosheet, which is prepared by a preparation method comprising the following specific steps, wherein the process flow chart of the preparation method is as follows: Figure 1 As shown:

[0050] Step 1: Weigh 1 mmol of V2O3 and 1.3 mmol of VCl3 respectively, mix them and put them into a quartz tube, seal the tube and place the quartz tube in a double-temperature controlled tube furnace to obtain VOCl single crystal by chemical vapor transport method;

[0051] Among them, the vacuum degree of chemical vapor transport method is less than 10 -3 mbar, the temperature is controlled at 750-800℃, that is, the raw material end is 800℃, the product end is 750℃, and the time is 7 days;

[0052] Step 2: First, the VOCl single crystal is pressed to obtain a VOCl single crystal, and then 0.03mmol of tetrahexylammonium bromide is weighed and dissolved in 10mL of acetonitrile to obtain an acetonitrile solution of tetrahexylammonium bromide. Subsequently, the VOCl single crystal is clamped with tweezers as a cathode, Pt as a counter electrode, and the acetonitrile solution of tetrahexylammonium bromide as an electrolyte. A voltage of -5V is applied, and a large number of VOCl single-layer nanosheets are obtained by electrochemical intercalation and stripping;

[0053] Step 3: Disperse VOCl monolayer nanosheets in N,N-dimethylformamide, use a rubber-tipped dropper to absorb a small amount of VOCl monolayer nanosheet dimethylformamide solution and drop it on the silicon wafer. After drying, place the silicon wafer in an argon atmosphere and anneal it at 500℃ for 2h to obtain large-sized monoclinic VO2 nanosheets attached to the silicon wafer.

[0054] The Raman scattering spectrum, atomic force microscope image, ordinary optical microscope image and scanning electron microscope image of the large-sized monoclinic VO2 nanosheet prepared in this embodiment are shown in Figures 1 and 2. Figure 3-Figure 6 As shown. Figure 3 It can be seen from the Raman scattering spectrum shown that the large-sized nanosheets prepared in this embodiment are pure monoclinic VO2 phase with good crystallinity. Figure 4a-4b It can be seen from the atomic force microscope image shown in the figure that the thickness of the large-sized monoclinic VO2 nanosheets prepared in this embodiment is within 1 nm. Figure 5 The ordinary optical microscope picture shown and Figure 6 It can be seen from the scanning electron microscope image shown that the lateral size of the large-sized monoclinic VO2 nanosheets prepared in this embodiment reaches 35 μm.

[0055] Example 2

[0056] This embodiment provides a large-sized monoclinic VO2 thin film, which is prepared by a preparation method including the following specific steps, wherein the process flow chart of the preparation method is as follows: Figure 2 As shown:

[0057] Step 1: Weigh 1 mmol of V2O3 and 1 mmol of VCl3 respectively, mix them and put them into a quartz tube, seal the tube and place the quartz tube in a double-temperature controlled tube furnace to obtain VOCl single crystal by chemical vapor transport method;

[0058] Among them, the vacuum degree of chemical vapor transport method is less than 10 -3 mbar, the temperature is controlled at 750-800℃, that is, the raw material end is 800℃, the product end is 750℃, and the time is 7 days;

[0059] Step 2: First, the VOCl single crystal is pressed to obtain a VOCl single crystal, and then 0.03mmol of tetrahexylammonium bromide is weighed and dissolved in 10mL of acetonitrile to obtain an acetonitrile solution of tetrahexylammonium bromide. Then, the VOCl single crystal is clamped with tweezers as the cathode, Pt as the counter electrode, and the acetonitrile solution of tetrahexylammonium bromide as the electrolyte. A voltage of -5V is applied, and a large number of VOCl single-layer nanosheets are obtained by electrochemical intercalation and stripping;

[0060] Step 3: Disperse VOCl monolayer nanosheets in N,N-dimethylformamide, use a rubber-tipped dropper to absorb the N,N-dimethylformamide solution of VOCl monolayer nanosheets and drop it on the organic filter membrane, then filter to obtain the VOCl thin film, then transfer the VOCl thin film on the organic filter membrane to a silicon wafer for drying, and finally place the VOCl thin film attached to the silicon wafer after drying in an argon atmosphere and anneal at 500°C for 2h to obtain a large-sized monoclinic VO2 thin film attached to the silicon wafer.

[0061] The Raman scattering spectrum and ordinary optical microscope image of the large-sized monoclinic VO2 thin film prepared in this embodiment are shown in Figure 2. Figure 7-Figure 8 As shown. Figure 7 It can be seen from the Raman scattering spectrum shown that the large-scale film prepared in this embodiment is a pure phase of monoclinic VO2 with good crystallinity and a thickness of less than 1 nm. Figure 8 It can be seen from the ordinary optical microscope picture shown that the large-sized monoclinic VO2 film prepared in this embodiment has good continuity and the lateral size reaches 500 μm.

[0062] The above is only a specific embodiment of the present invention, and cannot be used to limit the scope of the invention. Therefore, the replacement of equivalent components, or equivalent changes and modifications made according to the protection scope of the patent of the present invention, should still fall within the scope of this patent. In addition, the technical features of the present invention can be freely combined with each other, with each other and with each other, and with each other.

Claims

1. A method for preparing large-sized monoclinic VO2 nanosheets or thin films, characterized in that: The preparation method comprises: Step 1: Using VCl3 and V2O3 as raw materials, VOCl single crystal is prepared by chemical vapor transport method; Step 2: Pressing the VOCl single crystal into a VOCl single crystal, and then using the VOCl single crystal as a cathode and platinum as a counter electrode, electrochemical intercalation and exfoliation in an organic salt electrolyte to obtain a VOCl single-layer nanosheet; Step 3: Disperse the VOCl monolayer nanosheets in a polar organic solvent, and then drop the resulting solution onto a substrate material and dry it; or drop the resulting solution onto an organic filter membrane and then filter to obtain a VOCl film, and then transfer the VOCl film onto a substrate material and dry it; Step 4: In an inert atmosphere, annealing the VOCl single-layer nanosheet or VOCl film attached to the silicon wafer after drying to obtain a large-sized monoclinic VO2 nanosheet or a large-sized monoclinic VO2 film.

2. The preparation method according to claim 1, characterized in that: In step 1, the molar ratio of V2O3 to VCl3 is 1:1-10.

3. The preparation method according to claim 1 or 2, characterized in that: In step 1, the vacuum degree of chemical vapor transport is less than 10 -3 mbar, the temperature adopts 750-800℃ dual temperature control.

4. The preparation method according to claim 1, characterized in that: In step 2, the organic salt in the organic salt electrolyte includes one or a combination of tetrabutylammonium bromide, tetrahexylammonium bromide and tetra-n-octylammonium bromide.

5. The preparation method according to claim 1 or 4, characterized in that: In step 2, the concentration of the organic salt in the organic salt electrolyte is 1-500 mM, preferably 2-10 mM.

6. The preparation method according to claim 1 or 4, characterized in that: In step 2, the voltage used for electrochemical intercalation stripping is -5 to -10V.

7. The preparation method according to claim 1, characterized in that: In step three, the polar organic solvent includes N,N-dimethylformamide, isopropyl alcohol, dimethyl sulfoxide, N-methylpyrrolidone or propylene carbonate.

8. The preparation method according to claim 1 or 7, characterized in that: In step three, the substrate material includes silicon wafer, quartz wafer, sapphire or mica.

9. The preparation method according to claim 1, characterized in that: In step 4, the inert atmosphere includes argon atmosphere, nitrogen atmosphere or hydrogen-argon mixed gas atmosphere.

10. The preparation method according to claim 1 or 9, characterized in that: In step 4, the annealing temperature is 450-550°C, and the constant temperature time is more than 30 minutes, preferably 0.5-3 hours; Also preferably, the heating rate during the annealing process is 5-20 K / min.

11. A large-sized monoclinic VO2 nanosheet or a large-sized monoclinic VO2 film, characterized in that: The large-sized monoclinic VO2 nanosheet or large-sized monoclinic VO2 film is prepared by the preparation method of the large-sized monoclinic VO2 nanosheet or VO2 film according to any one of claims 1-10.

12. The large-sized monoclinic VO2 nanosheet or large-sized monoclinic VO2 thin film according to claim 11, characterized in that: The thickness of the large-sized monoclinic VO2 nanosheets and large-sized monoclinic VO2 films is adjustable and the thinnest is less than 1 nm. The lateral size of the large-sized monoclinic VO2 nanosheets is 1-50 μm, and the lateral size of the large-sized monoclinic VO2 films is above 500 μm.

13. Application of the large-sized monoclinic VO2 nanosheets or large-sized monoclinic VO2 films according to claim 11 or 12 in smart windows, sensors, field effect transistors or energy storage devices.

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