Vanadium dioxide composite microcapsule, and preparation method and application thereof

Abstract

The application belongs to the technical field of composite functional materials, and provides a vanadium dioxide composite microcapsule, 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 light-heat conversion material, and the light-heat conversion material is a transition metal compound or a high molecular polymer.The light-heat conversion material (a transition metal compound or a high molecular polymer) is used as the shell layer, the light-heat effect of the shell layer can convert solar energy into heat energy, induce local temperature rise, and drive vanadium dioxide to occur phase change under room temperature environment.Therefore, in the case that external temperature is insufficient to make vanadium dioxide occur phase change, the shell layer can convert light energy into heat energy, so that the temperature around vanadium dioxide reaches the phase change temperature, and phase change conversion is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite functional materials, and particularly relates to a vanadium dioxide composite microcapsule and a preparation method and application thereof. BACKGROUND

[0002] Vanadium dioxide (VO2) is a typical thermochromic material. Due to its phase transition temperature (about 68℃) near room temperature and the dramatic change in optical transmittance, it has become a hot spot in the field of smart windows. VO2 undergoes a Metal to Insulator Transition (MIT) during phase transition, accompanied by many changes in physical properties, such as 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 relatively 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 high phase transition temperature. SUMMARY

[0004] Therefore, the present application provides a vanadium dioxide composite microcapsule and a preparation method and application thereof. The vanadium dioxide composite microcapsule provided by the present application can undergo phase transition even when the external temperature does not reach the phase transition temperature.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

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

[0007] Preferably, the transition metal compound comprises one or more of titanium nitride, copper sulfide and tungsten oxide; and the high molecular polymer comprises 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 layer is 10-40 nm.

[0009] The present application also provides a preparation method of the vanadium dioxide composite microcapsule according to the above technical solutions, which comprises the following steps:

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

[0011] Mix the vanadium dioxide dispersion and a shell precursor reagent to perform in-situ reaction to obtain the vanadium dioxide composite microcapsule.

[0012] Preferably, the particle size of the vanadium dioxide powder is 30-60 nm; the surfactant comprises one or more of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, cetyl trimethyl ammonium bromide, cetyl trimethyl ammonium chloride and tris-hydroxymethyl aminomethane; the solvent comprises one or more of water and alcohol, and the alcohol comprises methanol and / or ethanol.

[0013] Preferably, the mass ratio of the vanadium dioxide powder and 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 and the shell precursor reagent is 0.2-0.7:0.6-30.

[0016] Preferably, when the shell is polydopamine, the shell precursor reagent is dopamine hydrochloride; the temperature of the in-situ reaction is 20-40℃, and the time is 20-30h.

[0017] Preferably, when the shell is titanium nitride, the shell precursor reagent is titanium isopropoxide, the temperature of the in-situ reaction is 20-40℃, and the time is 20-30h; after the in-situ reaction, further comprising performing nitriding treatment to obtain the vanadium dioxide composite microcapsule; the nitriding treatment comprises: first temperature rising to a first temperature for first holding, second temperature rising to a second temperature, third temperature rising to a third temperature for second holding; the first temperature rising rate is 4-7℃ / min, the first temperature is 400-500℃, the first holding time is 2-2.5h, and the atmosphere of the first temperature rising and first holding is air; the second temperature rising rate is 18-25℃ / min, the second temperature is 570-680℃, the third temperature rising rate is 3-3.5℃ / min, the third temperature is 700-850℃, and the second holding time is 7-8h; the atmosphere of the second temperature rising, third temperature rising and third holding is ammonia.

[0018] The application further provides the application of the vanadium dioxide composite microcapsule in the field of smart windows.

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

[0020] The present application takes a photothermal conversion material as a shell layer, and the photothermal effect of the shell layer can convert solar energy into heat energy to cause local temperature rise and drive vanadium dioxide to occur phase change at room temperature. Therefore, in the case that the external temperature is insufficient to cause vanadium dioxide to occur phase change, the shell layer can convert light energy into heat energy to make the temperature around vanadium dioxide reach the phase change temperature, and then realize phase change conversion, that is, the vanadium dioxide composite microcapsule will also occur phase change in the case that 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 microcapsule can be adjusted to adapt to the application requirements of different light intensity and temperature environments. The data of the embodiments show that the vanadium dioxide composite microcapsule provided by the present application has excellent photothermal conversion performance, solar light modulation capacity and near-infrared light modulation capacity. BRIEF DESCRIPTION OF DRAWINGS

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

[0022] Figure 2 It is a temperature-time curve of VO2, VO2@TiN obtained in Example 1 and VO2@PDA obtained in Example 3 under the condition of simulated sunlight (100 mw / cm 2 );

[0023] Figure 3 It is a solar light transmittance curve of VO2@TiN obtained in Example 2 at low temperature (25℃) and high temperature (80℃);

[0024] Figure 4 It is an appearance diagram of different materials immersed in hydrochloric acid solution. DETAILED DESCRIPTION

[0025] The present application provides a vanadium dioxide composite microcapsule, which comprises a core and a shell layer, the core is vanadium dioxide, and 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 application comprises a core, and the core is vanadium dioxide. In the present application, the particle size of the core is preferably 30-60 nm, and is specifically preferably 30 nm, 40 nm, 50 nm or 60 nm.

[0027] The vanadium dioxide composite microcapsule provided by the application comprises a shell layer, the shell layer is a photothermal conversion material, and the photothermal conversion material is a transition metal compound or a high polymer. In the application, the transition metal compound preferably comprises one or more of titanium nitride, copper sulfide and tungsten oxide, and is further preferably titanium nitride. In the application, the high polymer preferably comprises one or more of polydopamine and chitosan, and is further preferably polydopamine. In the application, the thickness of the shell layer is preferably 10-40 nm, and is particularly preferably 10 nm, 20 nm, 30 nm or 40 nm. In the application, the shell layer is made of a photothermal conversion material, and the photothermal effect of the shell layer can convert solar energy into heat energy to cause a local temperature rise and drive the core vanadium dioxide to undergo phase transition at room temperature. Therefore, in the case that the external temperature is insufficient to cause the core vanadium dioxide to undergo phase transition, the shell layer can convert light energy into heat energy to make the temperature around the core vanadium dioxide reach the phase transition temperature, and thus realize phase transition conversion. That is, the shell layer can make the vanadium dioxide composite microcapsule undergo phase transition without affecting the phase transition performance of vanadium dioxide in the case that the external temperature does not reach the phase transition temperature; in other words, the shell layer made of a photothermal conversion material improves the photothermal conversion performance of vanadium dioxide. At the same time, by adjusting the thickness of the shell layer, the photothermal conversion performance of the vanadium dioxide composite microcapsule can be adjusted to adapt to the application requirements of different light intensities and temperature environments. In addition, the shell layer can effectively isolate the vanadium dioxide from contact with oxygen and water, protect the vanadium dioxide from corrosion, and improve the weather resistance and stability of the vanadium dioxide.

[0028] The application further provides a preparation method of the vanadium dioxide composite microcapsule.

[0029] The vanadium dioxide powder and the surfactant are dispersed in a solvent to obtain a vanadium dioxide dispersion.

[0030] The vanadium dioxide dispersion and the shell layer precursor reagent are mixed to perform in-situ reaction, and the vanadium dioxide composite microcapsule is obtained.

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

[0032] The vanadium dioxide powder and the surfactant are dispersed in a solvent to obtain a vanadium dioxide dispersion.

[0033] In the application, the particle size of the vanadium dioxide powder is preferably 30-60 nm.

[0034] In the present application, the surfactant preferably comprises one or more of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, cetyl trimethyl ammonium bromide, cetyl trimethyl ammonium chloride and tris-hydroxymethyl aminomethane, and is further preferably cetyl trimethyl ammonium bromide and / or tris-hydroxymethyl aminomethane.

[0035] In the present application, the solvent preferably comprises one or more of water and alcohol. In the present application, the alcohol preferably comprises methanol and / or ethanol, and is further preferably ethanol.

[0036] In the present application, the dispersing of the vanadium dioxide powder and the surfactant in the solvent preferably comprises dispersing the vanadium dioxide powder in the solvent, performing ultrasonic treatment, and then adding the surfactant; the power of the ultrasonic treatment is preferably 20-40 kHz, and is particularly preferably 20 kHz, 25 kHz, 30 kHz, 35 kHz or 40 kHz; the time is preferably 10-30 min, and is particularly preferably 10 min, 15 min, 20 min, 25 min or 30 min.

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

[0038] In the present application, 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; the present application does not make a specific limitation on the amount of the inorganic base, as long as it can make the pH be 7.5-8.5.

[0039] After obtaining the vanadium dioxide dispersion, the present application mixes the vanadium dioxide dispersion and the shell precursor reagent, and performs in-situ reaction to obtain the vanadium dioxide composite microcapsule.

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

[0041] In the present application, the temperature of the in-situ reaction is preferably 20-40℃, and is particularly preferably 20℃, 30℃ or 40℃; the time is preferably 20-30 h, and is particularly preferably 20 h, 24 h or 30 h.

[0042] In the present application, 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, further preferably 0.2:0.6-0.9, and specifically preferably 0.7:0.6 or 0.7:0.9; after the in-situ reaction, preferably further comprising post-treatment, the post-treatment preferably comprises: centrifuging the obtained raw material reaction liquid, and sequentially washing and drying the obtained solid to obtain the vanadium dioxide composite microcapsule. In the present application, the washing reagent is preferably ethanol. In the present application, the drying temperature is preferably 50-140°C, further preferably 60-100°C; the pressure is preferably normal pressure; the time is preferably 12-24h; and the drying is preferably performed in an oven.

[0043] In the present application, 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 to the titanium isopropoxide is preferably 0.2-0.7:10-30, and more preferably 0.2:20 or 0.2:25. In the present application, 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, the solvent of the shell layer precursor reagent solution is preferably an alcohol, and the alcohol is further preferably ethanol; the concentration of the shell layer precursor reagent solution is preferably 1 g / mL. In the present application, when the shell layer precursor reagent is preferably titanium isopropoxide, the mixing method of the vanadium dioxide dispersion liquid and the shell layer precursor reagent is preferably adding the shell layer precursor reagent solution to the vanadium dioxide dispersion liquid, and the shell layer precursor reagent solution is preferably added dropwise. In the present application, when the shell layer precursor reagent is preferably titanium isopropoxide, after the in-situ reaction, a nitriding treatment is further performed to obtain the vanadium dioxide composite microcapsule; the nitriding treatment preferably comprises: first temperature rising to perform first holding at a first temperature, second temperature rising, third temperature rising to perform second holding at a third temperature; the first temperature rising rate is preferably 4-7 ℃ / min, and more preferably 4 ℃ / min, 5 ℃ / min, 6 ℃ / min or 7 ℃ / min, the first temperature is preferably 400-500 ℃, and more preferably 400 ℃, 450 ℃ or 500 ℃, the first holding time is preferably 2-2.5 h, and more preferably 2 h or 2.5 h, and the atmosphere of the first temperature rising and the first holding is preferably air; the second temperature rising rate is preferably 18-25 ℃ / min, and more preferably 18 ℃ / min, 20 ℃ / min or 25 ℃ / min, the second temperature is preferably 570-680 ℃, and more preferably 570 ℃, 600 ℃, 650 ℃ or 680 ℃, the third temperature rising rate is preferably 3-3.5 ℃ / min, and more preferably 3 ℃ / min or 3.5 ℃ / min, the third temperature is preferably 700-850 ℃, and more preferably 700 ℃, 750 ℃, 800 ℃ or 850 ℃, and the second holding time is preferably 7-8 h, and more preferably 7 h, 7.5 h or 8 h, and the atmosphere of the second temperature rising, the third temperature rising and the third holding is preferably ammonia.

[0044] In the present application, when the shell layer is titanium nitride, after the in-situ reaction, before the nitriding treatment, a post-treatment is preferably further performed, and the steps of the post-treatment are preferably consistent with the above technical solution, which will not be described herein.

[0045] The present application also provides the application of the vanadium dioxide composite microcapsule in the above technical solution or the vanadium dioxide composite microcapsule prepared by the preparation method in the field of intelligent windows.

[0046] The application mode of the vanadium dioxide composite microcapsule is not specifically limited, and a person skilled in the art can set it according to actual needs.

[0047] The vanadium dioxide composite microcapsule, the preparation method and the application thereof provided by the application will be described in detail below in combination with examples, but they cannot be understood as limitations to the protection scope of the application.

[0048] Example 1

[0049] A vanadium dioxide composite microcapsule, and a preparation method thereof includes the following steps:

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

[0051] S2: 0.3g of cetyltrimethylammonium bromide surfactant is added to the obtained mixed system, then 1.2mL of ammonia water is added, and stirring is performed until the system has a pH value of 8.5 to obtain a VO2 dispersion liquid; then, 20mL of a titanium isopropoxide ethanol solution (the concentration of titanium isopropoxide is 1g / mL) is added dropwise to the obtained VO2 dispersion liquid, and reaction is performed at 25℃ for 30h.

[0052] S3: after the in-situ reaction is completed, ethanol washing, centrifugation and drying are performed, and then the product is placed in an oven for drying to obtain a thermochromic VO2@TiO2 core-shell structure particle; the thermochromic VO2@TiO2 core-shell structure particle is placed in a tube furnace, and is kept at 450℃ for 2h under an air atmosphere (the heating rate is 5℃ / min); then, the above product is heated to 600℃ at a rate of 20℃ / min under an NH3 atmosphere, and then heated to 800℃ at a rate of 3℃ / min and kept for 7.5h, and finally a vanadium dioxide composite microcapsule (VO2@TiN) is obtained, wherein the particle size of the vanadium dioxide is 40nm, and the thickness of the TiN is 10nm.

[0053] Example 2

[0054] A vanadium dioxide composite microcapsule, and a preparation method thereof includes the following steps:

[0055] S1: 0.2g VO2 powder (particle size 40nm) is weighed, the VO2 powder is fully dispersed in 400mL ethanol, and ultrasonic treatment is performed at a power of 40kHz for 20min to obtain a mixed system.

[0056] S2: 0.3 g of cetyltrimethylammonium bromide was added to the obtained mixed system, and then 1.2 mL of ammonia water was added and stirred until the pH value of the system was 7.5, to obtain a VO2 dispersion liquid; then, 25 mL of a titanium isopropoxide ethanol solution (the concentration of the titanium isopropoxide was 1 g / mL) was added dropwise to the obtained VO2 dispersion liquid, and in-situ reaction was performed at 25°C for 30 h.

[0057] S3: After the in-situ reaction was completed, the VO2@TiO2 core-shell structure particles were obtained by ethanol washing, centrifugation, drying, and then being placed in an oven for drying; the VO2@TiO2 core-shell structure particles were placed in a tube furnace, and were kept at 450°C for 2 h under an air atmosphere (the temperature rising rate was 5°C / min); then, the above product was heated to 600°C at a temperature rising rate of 20°C / min, and then was heated to 800°C at a temperature rising rate of 3°C / min and was kept at 800°C for 7.5 h under an NH3 atmosphere, to finally obtain a vanadium dioxide composite microcapsule (VO2@TiN), wherein the particle size of the vanadium dioxide was 50 nm, and the thickness of the TiN was 20 nm.

[0058] Example 3

[0059] A vanadium dioxide composite microcapsule, and a preparation method thereof, the preparation method comprising the following steps:

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

[0061] S2: 0.6 g of dopamine hydrochloride (DA) was added to the VO2 dispersion liquid, and in-situ reaction was performed at 30°C for 24 h.

[0062] S3: After the in-situ reaction was completed, the VO2@PDA core-shell structure particles were cleaned with ethanol for multiple times, and then the product was placed in a 60°C oven for drying for 12 h, to obtain a vanadium dioxide composite microcapsule (VO2@PDA), wherein the particle size of the vanadium dioxide was 50 nm, and the thickness of the PDA was 20 nm.

[0063] Example 4

[0064] A vanadium dioxide composite microcapsule, and a preparation method thereof, the preparation method comprising the following steps:

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

[0066] S4: 0.9 g of dopamine hydrochloride (DA) was added to the VO2 dispersion liquid, and in-situ reaction was performed at 30°C for 24 h.

[0067] S5: After the in-situ reaction is completed, the VO2@PDA core-shell structure particle is cleaned multiple times using ethanol, and after the cleaning is completed, the product is placed in a 60℃ oven to dry for 12h to obtain a vanadium dioxide composite microcapsule (VO2@PDA), wherein the particle size of the vanadium dioxide is 50nm, and the thickness of the PDA is 40nm.

[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 Test

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

[0072] Figure 2 The temperature-time curve of VO2, VO2@TiN obtained in Example 1 and VO2@PDA obtained in Example 3 under simulated sunlight irradiation (100mw / cm 2 ) conditions is shown in FIG. 2. Figure 2 It can be seen from FIG. 2 that VO2@TiN has more excellent light-heat conversion performance.

[0073] Figure 3 The solar light transmittance curve of VO2@TiN obtained in Example 2 at low temperature (25℃) and high temperature (80℃) is shown in FIG. 3. Figure 3 It can be seen from FIG. 3 that the near-infrared light modulation ability of VO2@TiN is excellent.

[0074] VO2@TiN obtained in Example 2 is placed in a 1mol / L hydrochloric acid solution for 12h, and the result is that VO2@TiN has good environmental stability and can maintain in an acidic environment for 12h.

[0075] The spectral ability of VO2@TiN obtained in Example 2 is tested by GB / T 2680-2021, and the result is shown in Table 1.

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

[0077]

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

[0079] 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 system state was observed, and the results are shown in Figure 4 Figure 4 Figures showing the appearance of different materials immersed in a hydrochloric acid solution, wherein (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 placed in a hydrochloric acid solution for 10 min, the solution immediately turned blue, which was due to the blue color of V 4+ In contrast, VO2@TiN and VO2@PDA did not immediately turn blue when placed in a hydrochloric acid solution and remained black. After 60 min, 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 was due to the protective effect of the TiN shell layer; PDA was chemically inert and could protect VO2 from erosion.

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

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

[0082]

[0083] As can be seen from Table 2, the sunlight modulation ability of VO2@PDA obtained in Example 4 reached 6.09%, and the near-infrared modulation ability reached 14.9%.

[0084] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered within the scope of protection of the present application.​

Claims

1. A vanadium dioxide composite microcapsule, characterized by, The core is vanadium dioxide, and the shell layer is a photo-thermal conversion material which is a transition metal compound; The transition metal compound is titanium nitride; The preparation method of the vanadium dioxide composite microcapsule comprises the following steps: dispersing vanadium dioxide powder and a surfactant in a solvent to obtain a vanadium dioxide dispersion; mixing the vanadium dioxide dispersion and a shell layer precursor reagent, and sequentially performing in-situ reaction and nitriding treatment to obtain the vanadium dioxide composite microcapsule; The shell layer precursor reagent is titanium isopropoxide, the temperature of the in-situ reaction is 20-40 DEG C, and the time is 20-30 h; after the in-situ reaction, the nitriding treatment is further performed to obtain the vanadium dioxide composite microcapsule; The nitriding treatment comprises: first temperature rising to a first temperature for first holding, second temperature rising to a second temperature, and third temperature rising to a third temperature for second holding; the first temperature rising rate is 4-7 DEG C / min, the first temperature is 400-500 DEG C, the first holding time is 2-2.5 h, and the atmosphere of the first temperature rising and first holding is air; the second temperature rising rate is 18-25 DEG C / min, the second temperature is 570-680 DEG C, the third temperature rising rate is 3-3.5 DEG C / min, the third temperature is 700-850 DEG C, and the second holding time is 7-8 h; the atmosphere of the second temperature rising, third temperature rising and second holding is ammonia.

2. 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 layer is 10-40 nm.

3. The method for producing the vanadium dioxide composite microcapsule according to any one of claims 1 to 2, characterized by, The preparation method of the vanadium dioxide composite microcapsule comprises the following steps: dispersing vanadium dioxide powder and a surfactant in a solvent to obtain a vanadium dioxide dispersion; mixing the vanadium dioxide dispersion and a shell layer precursor reagent, and sequentially performing in-situ reaction and nitriding treatment to obtain the vanadium dioxide composite microcapsule; The shell layer precursor reagent is titanium isopropoxide, the temperature of the in-situ reaction is 20-40 DEG C, and the time is 20-30 h; after the in-situ reaction, the nitriding treatment is further performed to obtain the vanadium dioxide composite microcapsule; The nitriding treatment comprises: first temperature rising to a first temperature for first holding, second temperature rising to a second temperature, and third temperature rising to a third temperature for second holding; The first temperature rising rate is 4-7 DEG C / min, the first temperature is 400-500 DEG C, the first holding time is 2-2.5 h, and the atmosphere of the first temperature rising and first holding is air; the second temperature rising rate is 18-25 DEG C / min, the second temperature is 570-680 DEG C, the third temperature rising rate is 3-3.5 DEG C / min, the third temperature is 700-850 DEG C, and the second holding time is 7-8 h; the atmosphere of the second temperature rising, third temperature rising and second holding is ammonia.

4. The preparation method according to claim 3, characterized in that, The particle size of the vanadium dioxide powder is 30-60 nm; the surfactant comprises one or more of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, cetyl trimethyl ammonium bromide, cetyl trimethyl ammonium chloride and tris-hydroxymethyl aminomethane; and the solvent comprises one or more of water and alcohol, and the alcohol comprises methanol and / or ethanol.

5. The production method according to claim 3 or 4, characterized by, The mass ratio of the vanadium dioxide powder and the surfactant is 0.2-0.7:0.2-4. The pH of the vanadium dioxide dispersion is 7.5-8.

5.

6. The preparation method according to claim 3, characterized in that, The mass ratio of the vanadium dioxide powder and the shell precursor reagent is 0.2-0.7:0.6-30.

7. The vanadium dioxide composite microcapsule of any one of claims 1-2 or prepared by the method of any one of claims 3-6 for use in the field of smart windows.

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