Vanadium dioxide composite microcapsule as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of composite functional materials, and provides a vanadium dioxide composite microcapsule as well as a preparation method and application thereof. The vanadium dioxide composite microcapsule comprises a core and a shell layer, the core is vanadium dioxide, the shell layer is a photo-thermal conversion material, and the photo-thermal conversion material is a transition metal compound or a high-molecular polymer. A photo-thermal conversion material (a transition metal compound or a high-molecular polymer) is used as a shell layer, the photo-thermal effect of the shell layer can convert solar energy into heat energy, local temperature rise is triggered, and vanadium dioxide is driven to generate phase change in a room temperature environment. Therefore, under the condition that the external temperature is not enough to enable the vanadium dioxide to generate phase change, as the shell layer can convert light energy into heat energy, the surrounding temperature of the vanadium dioxide reaches the phase change temperature, and then phase change conversion is realized.

Description

Technical Field

[0001] The invention relates to the technical field of composite functional materials, and in particular to a vanadium dioxide composite microcapsule and a preparation method and application thereof. Background Art

[0002] As a typical thermochromic material, vanadium dioxide (VO2) has become a hot topic in the field of smart windows due to its phase transition temperature near room temperature (about 68°C) and the accompanying drastic change in optical transmittance. VO2 undergoes a metal to insulator transition (MIT) during phase change, accompanied by many changes in physical properties, such as a significant improvement in optical performance. Although VO2 has great potential in the field of smart windows, its practical application still faces technical challenges, including a high intrinsic phase transition temperature.

[0003] In practical applications, in order to improve the stability and durability of VO2, researchers have developed VO2 core-shell structure particles. This structure can improve the weather resistance of VO2 by wrapping a protective layer (such as SiO2, ZnO) on the surface of VO2 particles, preventing it from reacting with oxygen and water in the air, thereby maintaining the stability of VO2. However, these protective layers cannot improve the disadvantage of its high phase transition temperature. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a vanadium dioxide composite microcapsule and a preparation method and application thereof. The vanadium dioxide composite microcapsule provided by the present invention will also undergo phase transition when the external temperature does not reach the phase transition temperature.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a vanadium dioxide composite microcapsule, comprising a core and a shell layer, wherein the core is vanadium dioxide, the shell layer is a photothermal conversion material, and the photothermal conversion material is a transition metal compound or a high molecular polymer.

[0007] Preferably, the transition metal compound includes one or more of titanium nitride, copper sulfide and tungsten oxide; and the high molecular polymer includes one or more of polydopamine and chitosan.

[0008] Preferably, the particle size of the core is 30-60 nm, and the thickness of the shell is 10-40 nm.

[0009] The present invention also provides a method for preparing the vanadium dioxide composite microcapsules described in the above technical solution, comprising the following steps:

[0010] Dispersing vanadium dioxide powder and a surfactant in a solvent to obtain a vanadium dioxide dispersion;

[0011] The vanadium dioxide dispersion and the shell precursor reagent are mixed and reacted in situ to obtain the vanadium dioxide composite microcapsules.

[0012] Preferably, the particle size of the vanadium dioxide powder is 30 to 60 nm; the surfactant includes one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride and tris(hydroxymethyl)aminomethane; the solvent includes one or more of water and alcohol, and the alcohol includes methanol and / or ethanol.

[0013] Preferably, the mass ratio of the vanadium dioxide powder to the surfactant is 0.2-0.7:0.2-4;

[0014] The pH of the vanadium dioxide dispersion is 7.5-8.5.

[0015] Preferably, the mass ratio of the vanadium dioxide powder to the shell precursor reagent is 0.2-0.7:0.6-30.

[0016] Preferably, when the shell layer is polydopamine, the shell layer precursor reagent is dopamine hydrochloride; the temperature of the in-situ reaction is 20 to 40° C., and the time is 20 to 30 hours.

[0017] Preferably, when the shell layer is titanium nitride, the shell layer precursor reagent is titanium isopropoxide, the temperature of the in-situ reaction is 20-40°C, and the time is 20-30h; after the in-situ reaction, it also includes a nitriding treatment to obtain the vanadium dioxide composite microcapsules; the nitriding treatment includes: a first heating to a first temperature for a first insulation, a second heating to a second temperature, and a third heating to a third temperature for a second insulation; the first heating rate is 4-7°C / min, the first temperature is 400-500°C, the first insulation time is 2-2.5h, and the atmosphere of the first heating and the first insulation is air; the second heating rate is 18-25°C / min, the second temperature is 570-680°C, the third heating rate is 3-3.5°C / min, the third temperature is 700-850°C, the second insulation time is 7-8h, and the atmosphere of the second heating, the third heating and the third insulation is ammonia.

[0018] The present invention also provides the use of the vanadium dioxide composite microcapsules described in the above technical solution or the vanadium dioxide composite microcapsules prepared by the preparation method described in the above technical solution in the field of smart windows.

[0019] The invention provides a vanadium dioxide composite microcapsule.

[0020] The present invention uses a photothermal conversion material as a shell layer, and the photothermal effect of the shell layer can convert sunlight energy into thermal energy, causing a local temperature rise, and driving the vanadium dioxide to undergo a phase change under room temperature. Therefore, when the external temperature is not enough for the vanadium dioxide to undergo a phase change, the shell layer can convert light energy into thermal energy, so that the temperature around the vanadium dioxide reaches the phase change temperature, thereby achieving a phase change conversion, that is, the vanadium dioxide composite microcapsules will also undergo a phase change when the external temperature does not reach the phase change temperature. By adjusting the thickness of the shell layer, the photothermal conversion performance of the vanadium dioxide composite microcapsules can be adjusted to adapt to the application requirements of different light intensities and temperature environments. The data of the embodiment show that the vanadium dioxide composite microcapsules provided by the present invention have excellent photothermal conversion performance, sunlight modulation capability, and near-infrared light modulation capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a physical photo of VO2@TiN obtained in Example 1;

[0022] Figure 2 VO2, VO2@TiN obtained in Example 1, and VO2@PDA obtained in Example 3 were subjected to simulated sunlight (100 mw / cm 2 ) temperature-time curve under the conditions;

[0023] Figure 3 The solar transmittance curves of VO2@TiN obtained in Example 2 at low temperature (25°C) and high temperature (80°C);

[0024] Figure 4 These are the appearance pictures of different materials immersed in hydrochloric acid solution. DETAILED DESCRIPTION

[0025] The invention provides a vanadium dioxide composite microcapsule, comprising a core and a shell layer, wherein the core is vanadium dioxide, the shell layer is a photothermal conversion material, and the photothermal conversion material is a transition metal compound or a high molecular polymer.

[0026] The vanadium dioxide composite microcapsule provided by the present invention comprises a core, wherein the core is vanadium dioxide. In the present invention, the particle size of the core is preferably 30 to 60 nm, and more preferably 30 nm, 40 nm, 50 nm or 60 nm.

[0027] The vanadium dioxide composite microcapsules provided by the present invention include a shell layer, and the shell layer is a photothermal conversion material, and the photothermal conversion material is a transition metal compound or a polymer. In the present invention, the transition metal compound preferably includes one or more of titanium nitride, copper sulfide and tungsten oxide, and is more preferably titanium nitride. In the present invention, the polymer preferably includes one or more of polydopamine and chitosan, and is more preferably polydopamine. In the present invention, the thickness of the shell layer is preferably 10 to 40 nm, and is specifically preferably 10 nm, 20 nm, 30 nm or 40 nm. In the present invention, the photothermal conversion material is used as the shell layer, and the photothermal effect of the shell layer can convert solar energy into thermal energy, causing the local temperature to rise, and driving the core vanadium dioxide to undergo a phase change under room temperature. Therefore, when the external temperature is not enough to cause the core vanadium dioxide to undergo a phase change, the shell layer can convert light energy into thermal energy, so that the temperature around the core vanadium dioxide reaches the phase change temperature, thereby achieving a phase change conversion. That is, the setting of the shell layer can make the vanadium dioxide composite microcapsules undergo phase change when the external temperature does not reach the phase change temperature without affecting the phase change performance of vanadium dioxide; in other words, the photothermal conversion performance of vanadium dioxide is improved by using the photothermal conversion material as the shell material. At the same time, by adjusting the thickness of the shell layer, the photothermal conversion performance of the vanadium dioxide composite microcapsules can be adjusted to adapt to the application requirements of different light intensities and temperature environments. In addition, the setting of the shell layer can effectively isolate vanadium dioxide from contact with oxygen and water, protect vanadium dioxide from erosion, and improve the weather resistance and stability of vanadium dioxide.

[0028] The present invention also provides a method for preparing the vanadium dioxide composite microcapsules described in the above technical solution, comprising the following steps:

[0029] Dispersing vanadium dioxide powder and a surfactant in a solvent to obtain a vanadium dioxide dispersion;

[0030] The vanadium dioxide dispersion and the shell precursor reagent are mixed and reacted in situ to obtain the vanadium dioxide composite microcapsules.

[0031] Unless otherwise specified, the raw materials used in the present invention are preferably commercially available products.

[0032] The invention disperses vanadium dioxide powder and a surfactant in a solvent to obtain a vanadium dioxide dispersion.

[0033] In the present invention, the particle size of the vanadium dioxide powder is preferably 30 to 60 nm.

[0034] In the present invention, the surfactant preferably includes one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride and tris(hydroxymethyl)aminomethane, and more preferably hexadecyltrimethylammonium bromide and / or tris(hydroxymethyl)aminomethane.

[0035] In the present invention, the solvent preferably includes one or more of water and alcohol. In the present invention, the alcohol preferably includes methanol and / or ethanol, and more preferably ethanol.

[0036] In the present invention, dispersing the vanadium dioxide powder and the surfactant in a solvent preferably includes: dispersing the vanadium dioxide powder in a solvent, performing ultrasonic treatment, and then adding a surfactant; the power of the ultrasonic treatment is preferably 20 to 40 kHz, specifically preferably 20 kHz, 25 kHz, 30 kHz, 35 kHz or 40 kHz; the time is preferably 10 to 30 min, specifically preferably 10 min, 15 min, 20 min, 25 min or 30 min.

[0037] In the present invention, the mass ratio of the vanadium dioxide powder to the surfactant is preferably 0.2-0.7:0.2-4, and more preferably 0.2:0.3 or 0.7:3.63. In the present invention, the amount ratio of the vanadium dioxide powder to the solvent is preferably 0.2-0.7 g:300-400 mL, and more preferably 0.2 g:400 mL or 0.7 g:300 mL.

[0038] In the present invention, the pH of the vanadium dioxide dispersion is preferably 7.5-8.5; the pH of the vanadium dioxide dispersion is preferably achieved by adding an inorganic base, and the inorganic base is preferably ammonia water; the present invention does not specifically limit the amount of the inorganic base, as long as the pH can be 7.5-8.5.

[0039] After obtaining the vanadium dioxide dispersion, the present invention mixes the vanadium dioxide dispersion with a shell precursor reagent to perform an in-situ reaction to obtain the vanadium dioxide composite microcapsule.

[0040] In the present invention, the mass ratio of the vanadium dioxide powder to the shell precursor reagent is preferably 0.2-0.7:0.6-30.

[0041] In the present invention, the temperature of the in-situ reaction is preferably 20-40°C, specifically preferably 20°C, 30°C or 40°C; the time is preferably 20-30h, specifically preferably 20h, 24h or 30h.

[0042] In the present invention, when the shell layer is polydopamine, the shell layer precursor reagent is preferably dopamine hydrochloride; the mass ratio of the vanadium dioxide powder and dopamine hydrochloride is preferably 0.2-0.7:0.6-0.9, more preferably 0.2:0.6-0.9, specifically preferably 0.7:0.6 or 0.7:0.9; after the in-situ reaction, it is preferably further included in post-treatment, and the post-treatment preferably includes: centrifuging the obtained raw material reaction liquid, washing and drying the obtained solid in turn, to obtain the vanadium dioxide composite microcapsules. In the present invention, the washing reagent is preferably ethanol. In the present invention, the drying temperature is preferably 50-140°C, more preferably 60-100°C; the pressure is preferably normal pressure; the time is preferably 12-24h; the drying is preferably carried out in an oven.

[0043] In the present invention, when the shell layer is titanium nitride, the shell layer precursor reagent is preferably titanium isopropoxide, and the mass ratio of the vanadium dioxide powder and titanium isopropoxide is preferably 0.2-0.7:10-30, and specifically preferably 0.2:20 or 0.2:25. In the present invention, when the shell layer precursor reagent is preferably titanium isopropoxide, the shell layer precursor reagent is preferably used in the form of a shell layer precursor reagent solution, and the solvent of the shell layer precursor reagent solution is preferably alcohol, and the alcohol is further preferably ethanol; the concentration of the shell layer precursor reagent solution is preferably 1g / mL. In the present invention, when the shell layer precursor reagent is preferably titanium isopropoxide, the method of mixing the vanadium dioxide dispersion and the shell layer precursor reagent is preferably: adding the shell layer precursor reagent solution to the vanadium dioxide dispersion, and the method of adding the shell layer precursor reagent solution is preferably dropwise addition. In the present invention, when the shell precursor reagent is preferably titanium isopropoxide, after the in-situ reaction, it also includes a nitriding treatment to obtain the vanadium dioxide composite microcapsules; the nitriding treatment preferably includes: a first heating to a first temperature for a first insulation, a second heating to a second temperature, and a third heating to a third temperature for a second insulation; the first heating rate is preferably 4 to 7 ° C / min, specifically preferably 4 ° C / min, 5 ° C / min, 6 ° C / min or 7 ° C / min, the first temperature is preferably 400 to 500 ° C, specifically preferably 400 ° C, 450 ° C or 500 ° C, the first insulation time is preferably 2 to 2.5 h, specifically preferably 2 h or 2.5 h, the first heating and the first insulation atmosphere Preferably it is air; the second heating rate is preferably 18-25°C / min, specifically preferably 18°C / min, 20°C / min or 25°C / min, the second temperature is preferably 570-680°C, specifically preferably 570°C, 600°C, 650°C or 680°C, the third heating rate is preferably 3-3.5°C / min, specifically preferably 3°C / min or 3.5°C / min, the third temperature is preferably 700-850°C, specifically preferably 700°C, 750°C, 800°C or 850°C, the second insulation time is preferably 7-8h, specifically preferably 7h, 7.5h or 8h, and the atmosphere of the second heating, third heating and third insulation is preferably ammonia.

[0044] In the present invention, when the shell layer is titanium nitride, after the in-situ reaction and before the nitridation treatment, a post-treatment is preferably also included. The steps of the post-treatment are preferably consistent with the above technical solution and will not be repeated here.

[0045] The present invention also provides the use of the vanadium dioxide composite microcapsules described in the above technical solution or the vanadium dioxide composite microcapsules prepared by the preparation method described in the above technical solution in the field of smart windows.

[0046] The present invention does not specifically limit the application mode of the vanadium dioxide composite microcapsules, and those skilled in the art can configure the application mode according to actual needs.

[0047] The vanadium dioxide composite microcapsules provided by the present invention and their preparation method and application are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0048] Example 1

[0049] A vanadium dioxide composite microcapsule, the preparation method comprises the following steps:

[0050] S1: Weigh 0.2 g of VO2 powder (particle size 40 nm), fully disperse the VO2 powder in 400 mL of ethanol, and ultrasonicate at 40 kHz power for 20 min to obtain a mixed system.

[0051] S2: Add 0.3g of hexadecyltrimethylammonium bromide surfactant to the obtained mixed system, then add 1.2mL of ammonia water and stir evenly. The pH value of the system is 8.5, and a VO2 dispersion is obtained. Then, 20mL of isopropoxide titanium ethanol solution (the concentration of isopropoxide titanium is 1g / mL) is added dropwise to the obtained VO2 dispersion, and react at 25°C for 30h.

[0052] S3: After the in-situ reaction is completed, the particles are washed with ethanol, centrifuged, dried and then placed in an oven to obtain thermochromic VO2@TiO2 core-shell structure particles; the thermochromic VO2@TiO2 core-shell structure particles are placed in a tubular furnace and maintained at 450°C for 2 hours (heating rate of 5°C / min) under an air atmosphere; then, the above product is heated to 600°C at 20°C / min under an NH3 atmosphere, and then heated to 800°C at 3°C / min and maintained for 7.5 hours, finally obtaining vanadium dioxide composite microcapsules (VO2@TiN), wherein the particle size of vanadium dioxide is 40nm and the thickness of TiN is 10nm.

[0053] Example 2

[0054] A vanadium dioxide composite microcapsule, the preparation method comprises the following steps:

[0055] S1: Weigh 0.2 g of VO2 powder (particle size 50 nm), fully disperse the VO2 powder in 400 mL of ethanol, and ultrasonicate at 30 kHz power for 30 min to obtain a mixed system.

[0056] S2: Add 0.3g of hexadecyltrimethylammonium bromide to the obtained mixed system, then add 1.2mL of ammonia water and stir evenly, the pH value of the system is 7.5, and a VO2 dispersion is obtained; then, 25mL of titanium isopropoxide ethanol solution (the concentration of titanium isopropoxide is 1g / mL) is added dropwise to the obtained VO2 dispersion, and an in-situ reaction is carried out at 25°C for 30h.

[0057] S3: After the in-situ reaction is completed, the particles are washed with ethanol, centrifuged, dried and then placed in an oven to obtain thermochromic VO2@TiO2 core-shell structure particles; the thermochromic VO2@TiO2 core-shell structure particles are placed in a tubular furnace and maintained at 450°C for 2 hours (heating rate of 5°C / min) under an air atmosphere; then, the product is heated to 600°C at 20°C / min under an NH3 atmosphere, and then heated to 800°C at 3°C / min and maintained for 7.5 hours, finally obtaining vanadium dioxide composite microcapsules (VO2@TiN), wherein the particle size of vanadium dioxide is 50nm and the thickness of TiN is 20nm.

[0058] Example 3

[0059] A vanadium dioxide composite microcapsule, the preparation method comprises the following steps:

[0060] S1: Weigh 0.7 g of VO2 powder (particle size: 50 nm), and fully disperse the VO2 powder in 300 mL of water to which 3.63 g of tris(hydroxymethyl)aminomethane) was added and the pH was adjusted to 8 to 8.5 to obtain a VO2 dispersion.

[0061] S2: Add 0.6 g of dopamine hydrochloride (DA) to the VO2 dispersion and react in situ at 30°C for 24 hours.

[0062] S3: After the in-situ reaction is completed, the VO2@PDA core-shell structure particles are washed with ethanol for multiple times. After washing, the product is placed in a 60°C oven and dried for 12 hours to obtain vanadium dioxide composite microcapsules (VO2@PDA), wherein the particle size of vanadium dioxide is 50nm and the thickness of PDA is 20nm.

[0063] Example 4

[0064] A vanadium dioxide composite microcapsule, the preparation method comprises the following steps:

[0065] S3: Weigh 0.7 g of VO2 powder (particle size: 50 nm), and fully disperse the VO2 powder in 300 mL of water to which 3.63 g of tris(hydroxymethyl)aminomethane) was added and the pH was adjusted to 8 to 8.5 to obtain a VO2 dispersion.

[0066] S4: Add 0.9 g of dopamine hydrochloride (DA) to the VO2 dispersion and react in situ at 30°C for 24 h.

[0067] S5: After the in-situ reaction is completed, the VO2@PDA core-shell structure particles are washed with ethanol for multiple times. After washing, the product is placed in a 60°C oven and dried for 12 hours to obtain vanadium dioxide composite microcapsules (VO2@PDA), wherein the particle size of vanadium dioxide is 50 nm and the thickness of PDA is 40 nm.

[0068] Comparative Example 1

[0069] The difference from Example 1 is that titanium isopropoxide is replaced by tetrabutyl silicate to obtain VO2@SiO2.

[0070] Performance Testing

[0071] Figure 1 This is a photo of the VO2@TiN obtained in Example 1. Figure 1 It can be seen that the obtained VO2@TiN is a black granular powder.

[0072] Figure 2 VO2, VO2@TiN obtained in Example 1, and VO2@PDA obtained in Example 3 were subjected to simulated sunlight (100 mw / cm 2 ) conditions, the temperature-time curve from Figure 2 It can be seen that VO2@TiN has better light-to-heat conversion performance.

[0073] Figure 3 The solar transmittance curves of VO2@TiN obtained in Example 2 at low temperature (25°C) and high temperature (80°C) are shown in Table 2. Figure 3 It can be seen that VO2@TiN has excellent near-infrared light modulation ability.

[0074] The VO2@TiN obtained in Example 2 was placed in a 1 mol / L hydrochloric acid solution for 12 hours. The results showed that VO2@TiN had good environmental stability and could be maintained in an acidic environment for 12 hours.

[0075] The spectral capability of VO2@TiN obtained in Example 2 was tested using GB / T 2680-2021, and the results are shown in Table 1.

[0076] Table 1 Spectral capability of VO2@TiN obtained in Example 2

[0077]

[0078] It can be seen from Table 1 that the solar light modulation capability of VO2@TiN obtained in Example 2 reaches 6.75%, and the near-infrared modulation capability reaches 15.82%.

[0079] The vanadium dioxide powder, VO2@TiN obtained in Example 1 and Example 2, and VO2@PDA obtained in Example 4 were placed in a 1 mol / L hydrochloric acid solution and the state of the system was observed. The results are as follows: Figure 4 As shown, Figure 4 The appearance of different materials immersed in hydrochloric acid solution, among which (a) is vanadium dioxide powder, (b) is VO2@TiN obtained in Example 1, (c) is VO2@TiN obtained in Example 2, and (d) is VO2@PDA obtained in Example 4. Figure 4 It can be seen that after VO2 powder was put into hydrochloric acid solution for 10 minutes, the solution immediately turned blue. This is because V 4+ The blue color of the particles is caused by the fact that VO2@TiN and VO2@PDA, in contrast, VO2@TiN did not turn blue immediately after being placed in a hydrochloric acid solution, but remained black. After 60 minutes, the VO2 powder had turned dark blue, while VO2@TiN and VO2@PDA remained black, indicating that VO2@TiN resisted the erosion of hydrochloric acid, which is due to the protective effect of the TiN shell; PDA is chemically inert and can protect VO2 from erosion.

[0080] The spectral capability of VO2@PDA obtained in Example 4 was tested using GB / T 2680-2021, and the results are shown in Table 2.

[0081] Table 2 Spectral capability of VO2@PDA obtained in Example 4

[0082]

[0083] It can be seen from Table 2 that the solar light modulation capability of VO2@PDA obtained in Example 4 reaches 6.09%, and the near-infrared modulation capability reaches 14.9%.

[0084] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A vanadium dioxide composite microcapsule, characterized in that: It comprises a core and a shell layer, wherein the core is vanadium dioxide, the shell layer is a photothermal conversion material, and the photothermal conversion material is a transition metal compound or a high molecular polymer.

2. The vanadium dioxide composite microcapsule according to claim 1, characterized in that: The transition metal compound includes one or more of titanium nitride, copper sulfide and tungsten oxide; the high molecular polymer includes one or more of polydopamine and chitosan.

3. The vanadium dioxide composite microcapsule according to claim 1, characterized in that: The particle size of the core is 30-60 nm, and the thickness of the shell is 10-40 nm.

4. The method for preparing vanadium dioxide composite microcapsules according to any one of claims 1 to 3, characterized in that: The following steps are involved: Dispersing vanadium dioxide powder and a surfactant in a solvent to obtain a vanadium dioxide dispersion; The vanadium dioxide dispersion and the shell precursor reagent are mixed and reacted in situ to obtain the vanadium dioxide composite microcapsules.

5. The preparation method according to claim 4, characterized in that: The particle size of the vanadium dioxide powder is 30-60 nm; the surfactant includes one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride and tris(hydroxymethyl)aminomethane; the solvent includes one or more of water and alcohol, and the alcohol includes methanol and / or ethanol.

6. The preparation method according to claim 4 or 5, characterized in that: The mass ratio of the vanadium dioxide powder to the surfactant is 0.2-0.7:0.2-4; The pH of the vanadium dioxide dispersion is 7.5-8.

5.

7. The preparation method according to claim 4, characterized in that: The mass ratio of the vanadium dioxide powder to the shell precursor reagent is 0.2-0.7:0.6-30.

8. The preparation method according to claim 4, characterized in that: When the shell layer is polydopamine, the shell layer precursor reagent is dopamine hydrochloride; the temperature of the in-situ reaction is 20-40° C., and the time is 20-30 hours.

9. The preparation method according to claim 4, characterized in that: When the shell layer is titanium nitride, the shell layer precursor reagent is titanium isopropoxide, the temperature of the in-situ reaction is 20-40°C, and the time is 20-30h; after the in-situ reaction, a nitridation treatment is further performed to obtain the vanadium dioxide composite microcapsules; The nitriding treatment includes: first heating to a first temperature for first insulation, second heating to a second temperature, and third heating to a third temperature for second insulation; the first heating rate is 4-7°C / min, the first temperature is 400-500°C, the first insulation time is 2-2.5h, and the atmosphere of the first heating and the first insulation is air; the second heating rate is 18-25°C / min, the second temperature is 570-680°C, the third heating rate is 3-3.5°C / min, the third temperature is 700-850°C, the second insulation time is 7-8h, and the atmosphere of the second heating, the third heating and the third insulation is ammonia.

10. Use of the vanadium dioxide composite microcapsules described in any one of claims 1 to 3 or the vanadium dioxide composite microcapsules prepared by the preparation method described in any one of claims 4 to 9 in the field of smart windows.

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