Core-shell structure composite powder with vanadium dioxide coated with calcium fluoride and preparation method

Abstract

The invention belongs to the technical field of thermochromic functional materials, and particularly relates to calcium fluoride coated vanadium dioxide core-shell structure composite powder and a preparation method. The calcium fluoride coated vanadium dioxide core-shell structure composite powder provided by the invention comprises a plurality of core-shell particles, and each core-shell particle comprises a vanadium dioxide powder core and a calcium fluoride shell layer coated outside the vanadium dioxide powder. The vanadium dioxide powder core is coated with the calcium fluoride shell layer, the vanadium dioxide powder can be protected, the particle dispersity and oxidation resistance can be improved, the optical performance of the calcium fluoride coated vanadium dioxide core-shell structure composite powder can be synergistically improved, the visible light transmittance is improved, meanwhile, the sunlight modulation capacity is improved, and the application prospect is wide. The high light transmittance and low heat absorption are achieved, the energy-saving and consumption-reducing effects are achieved, and the material is suitable for the fields of intelligent temperature control windows, optical switches, thermochromic films and the like and has wide application prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermotropic functional materials, and more particularly relates to a core-shell structure composite powder of calcium fluoride coated vanadium dioxide and a preparation method. BACKGROUND

[0002] About one-third of the total energy consumption is used in the field of building, and half of the building energy consumption is used for air conditioning and heating. As the main way of energy exchange between indoor and outdoor, adjusting indoor temperature through windows is a feasible way to reduce building energy consumption.

[0003] Vanadium dioxide (VO2) as a typical thermotropic phase change material, undergoes reversible metal-insulator phase transition at about 68℃, accompanied by significant changes in electrical, optical and magnetic properties, and has broad application prospects in intelligent windows, optical switches, thermochromic materials and other fields. However, VO2 particles have low transmittance in the visible light region, are easy to oxidize, have poor particle dispersion performance, and are prone to agglomeration, making it difficult to prepare functional films with excellent optical performance and good uniformity, which limits its application in the optical field.

[0004] Currently, the problems of high phase transition temperature and low visible light transmittance of VO2-based materials are mainly solved by means of element doping, core-shell structure coating, and microstructure design. For example, patent document CN119775816A prepares a coated doped vanadium dioxide film by element doping combined with coated particle coating, so that the finished film realizes high transmittance, low phase transition temperature and strong weather resistance at the same time, but the solar light modulation ability is significantly reduced, and the ability to regulate indoor temperature is weak. Patent document CN116891649A prepares a vanadium dioxide composite functional powder (VE-VO2@TiO2-β-CD) by modifying vitamin E on the surface of vanadium dioxide, coating vanadium dioxide with TiO2 shell, and grafting β-cyclodextrin on the surface of TiO2 shell, which can improve the oxidation resistance and thermochromic weather resistance stability of vanadium dioxide, and improve the dispersibility of vanadium dioxide, optimize the visible light transmittance of the film, and enhance the self-cleaning, corrosion-resistant, and anti-fogging ability of the film. However, the volume fraction of VE-VO2@TiO2-β-CD in the slurry used to prepare the film needs to be maintained at a high level (volume fraction of 4%~6%) to optimize the solar light modulation ability of the film, and the preparation steps of the vanadium dioxide composite functional powder are complex, the production cost is high, and the popularization and application are difficult. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to provide a calcium fluoride coated vanadium dioxide core-shell structure composite powder and a preparation method, aiming to solve the problems of the prior art, such as complex preparation steps, high production cost, poor optical performance, especially weak solar light modulation capacity, etc., and to improve the visible light transmittance of the vanadium dioxide-based composite powder and the solar light modulation capacity while solving the problems of poor dispersibility and easy oxidation of vanadium dioxide materials.

[0006] To achieve the above-mentioned purpose, in a first aspect, the present application provides a calcium fluoride coated vanadium dioxide core-shell structure composite powder, which comprises a plurality of core-shell particles, wherein the core-shell particles comprise a vanadium dioxide powder core and a calcium fluoride shell layer coated on the vanadium dioxide powder.

[0007] Preferably, in the core-shell structure composite powder, the molar ratio of calcium to vanadium is (0.1-0.5):1.

[0008] Preferably, the vanadium dioxide powder is spherical or approximately spherical, and the particle size is ≤100 nm.

[0009] Preferably, the thickness of the calcium fluoride shell layer is 8-20 nm.

[0010] Preferably, the vanadium dioxide powder is a monoclinic vanadium dioxide powder.

[0011] In a second aspect, the present application provides a preparation method of the above-mentioned core-shell structure composite powder, comprising the following steps: S1. uniformly mixing vanadium dioxide powder and a surfactant in a polar solvent to obtain a vanadium dioxide powder dispersion; S2. uniformly mixing a water-soluble calcium salt and the vanadium dioxide powder dispersion, then adding a water-soluble fluoride for co-precipitation reaction, generating calcium fluoride precipitate on the surface of the vanadium dioxide powder, then standing and aging, so that the calcium fluoride precipitate is coated on the surface of the vanadium dioxide powder and forms an initial calcium fluoride shell layer; S3. collecting the reaction precipitate, washing and drying, then performing annealing treatment in a protective atmosphere to obtain the above-mentioned calcium fluoride coated vanadium dioxide core-shell structure composite powder.

[0012] Preferably, in step S1, the surfactant comprises a non-ionic surfactant and / or an anionic surfactant; and / or, The polar solvent comprises one or more of deionized water, anhydrous ethanol, ethylene glycol, isopropyl alcohol, acetone, and butanone; and / or, The amount of the surfactant is 5wt%-15wt% of the total mass of the vanadium dioxide powder.

[0013] Preferably, in step S1, the vanadium dioxide powder is prepared by a one-step hydrothermal method, including the following steps: mixing ammonium metavanadate and hydrazine monohydrochloride in a molar ratio of (2-3):1 in deionized water, then adding hydrochloric acid dropwise until the solution is blue and transparent, then adding ammonia water as a settling agent and adjusting the pH of the system to 7-8, collecting the brownish yellow soil colored precipitate, and ultrasonic dispersing it in deionized water in a reaction kettle at 210-280°C for 18-30h for hydrothermal reaction, centrifugation, washing, vacuum drying, to obtain the vanadium dioxide powder.

[0014] Preferably, in step S2, the water-soluble calcium salt is selected from one or more of calcium chloride, calcium acetate, calcium nitrate, and calcium nitrate hydrate; and / or, The water-soluble fluoride is selected from one or more of potassium fluoride, potassium fluoride hydrate, sodium fluoride, sodium fluoride hydrate, and ammonium fluoride.

[0015] Preferably, in step S2, the molar ratio of the water-soluble calcium salt to the vanadium dioxide powder is (0.1-0.5):1.

[0016] Preferably, in step S2, the molar ratio of the water-soluble calcium salt to the water-soluble fluoride is 1:(2-3).

[0017] Preferably, in step S2, the temperature of the co-precipitation reaction is 50-70°C, and the time of the co-precipitation reaction is 100-150min.

[0018] Preferably, in step S2, the temperature of the standing and aging is 20-30°C, and the time of the standing and aging is 10-15h.

[0019] Preferably, in step S3, the protective atmosphere is selected from one or more of nitrogen, argon, neon, helium, xenon, or krypton.

[0020] Preferably, in step S3, the temperature of the annealing treatment is 450-500°C, and the time of the annealing treatment is 2-4h.

[0021] In a third aspect, the present application provides a temperature control coating, which comprises the core-shell structure composite powder and an auxiliary agent.

[0022] Preferably, the auxiliary agent comprises one or more of an organic solvent, a film-forming agent, a binder, and a leveling agent.

[0023] In a fourth aspect, the present application provides an intelligent temperature control film, which is formed by applying the temperature control coating on the surface of a substrate and drying.

[0024] Preferably, the substrate comprises architectural glass, automotive glass, a plastic substrate, or a combination thereof.

[0025] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages: (1) The calcium fluoride coated vanadium dioxide core-shell structure composite powder provided by the present application contains a plurality of core-shell particles, which include a vanadium dioxide powder core and a calcium fluoride shell layer coated outside the vanadium dioxide powder, and can synergistically improve the optical performance of the calcium fluoride coated vanadium dioxide core-shell structure composite powder, improve the visible light transmittance while improving the solar light modulation capability, achieve high light transmittance and low heat absorption, achieve energy saving, comfort improvement and environmental protection benefits, and is suitable for application in intelligent temperature control windows, optical coatings and other application fields.

[0026] (2) By coating a calcium fluoride shell layer outside the vanadium dioxide powder core, the present application can also protect the vanadium dioxide powder, improve the oxidation resistance while reducing particle agglomeration and improving dispersibility, and can expand the application scenarios of vanadium dioxide nanomaterials. In addition, the above-mentioned calcium fluoride coated vanadium dioxide core-shell structure composite powder also has excellent thermal stability, can effectively prolong its service life and has wide environmental applicability. In actual production and application, it is beneficial to reduce the difficulty of preparing intelligent temperature control films by wet process, ensure uniform dispersion of the core-shell structure composite powder in the film, and thus obtain high-quality intelligent temperature control films with uniform function, stable performance and long service life.

[0027] (3) Compared with existing core-shell structure composite powders, when the calcium fluoride coated vanadium dioxide core-shell structure composite powder (VO2@CaF2 composite powder) provided by the present application is used to manufacture intelligent temperature control films, the weight percentage of VO2@CaF2 composite powder in the temperature control coating is only 3.38wt%, and the intelligent temperature control film with high visible light transmittance, strong solar light modulation capability, excellent oxidation resistance and good thermal stability can be prepared, the transmittance at 550nm in the visible light band can reach 55.8%, the solar light modulation capability (ΔT sol ) can reach 18.0%, and it remains yellow-free after being exposed to air at 300℃ for 6h, has excellent optical performance, good oxidation resistance, low manufacturing cost and other advantages, and is suitable for popularization and application.

[0028] (4) The present application performs surface modification and dispersion treatment on the vanadium dioxide powder, and forms a calcium fluoride coating layer on the surface of the vanadium dioxide powder through a coprecipitation reaction of water-soluble calcium source and water-soluble fluoride, and after annealing treatment, a core-shell structure composite powder with excellent optical performance of calcium fluoride shell layer coated vanadium dioxide core can be prepared. Compared with the prior art, the preparation method provided by the present application has the characteristics of simple process, mild reaction conditions, low energy consumption and environmental friendliness, and is suitable for large-scale production and manufacturing. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a preparation method flowchart of the calcium fluoride-coated vanadium dioxide composite powder with a core-shell structure provided in the embodiments of the present application; Figure 2 is an XRD pattern of the nano VO2 powder provided in the embodiments of the present application; Figure 3 is a micro-morphology of the nano VO2 powder provided in the embodiments of the present application; wherein content (a) and content (b) are SEM images and a particle size distribution column chart, respectively; Figure 4 is an XRD pattern of a series of VO2@CaF2 composite powders prepared in Embodiment 1 of the present application; Figure 5 is an SEM image of VO2@CaF2 composite powder S4 prepared in Embodiment 1 of the present application; wherein content (a) and content (b) are SEM images under a 100 nm scale and a 200 nm scale, respectively; Figure 6 is an XRD pattern of a series of VO2@CaF2 composite powders prepared in Embodiment 2 of the present application; Figure 7 is a TEM image of a series of VO2@CaF2 composite powders prepared in Embodiment 2 of the present application; Figure 8 is an SEM image of VO2@CaF2 composite powder S5' prepared in Embodiment 2 of the present application; wherein content (a) and content (b) are SEM images under a 100 nm scale and a 200 nm scale, respectively; Figure 9 is an EDS pattern of VO2@CaF2 composite powder S5' prepared in Embodiment 2 of the present application; Figure 10 is a real object image of a temperature control coating and an intelligent temperature control film prepared based on a series of VO2@CaF2 composite powders in Embodiment 2 of the present application; wherein content (a) is a real object image of the temperature control coating, and content (b) is a real object image of the intelligent temperature control film; Figure 11 is a transmittance change with wavelength of an intelligent temperature control film prepared based on a series of VO2@CaF2 composite powders in Embodiment 1 of the present application at different temperatures; Figure 12 is an anti-oxidation performance of an intelligent temperature control film prepared based on a series of VO2@CaF2 composite powders in Embodiment 1 of the present application when exposed to air and heated at 300℃ for 0~6h. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not intended to limit the present application.

[0031] In the description of the present application, it should be understood that the term "and / or" is a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. In this paper, the symbol " / " represents the relationship of or, for example, A / B represents A or B.

[0032] In the description of the embodiments of the present application, the words "exemplary" or "for example" are used to represent an example, illustration or description. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. Rather, the use of "exemplary" or "for example" is intended to present the relevant concept in a specific manner.

[0033] In the description of the embodiments of the present application, unless otherwise stated, "a plurality of" means two or more.

[0034] The present application provides a core-shell structure composite powder of calcium fluoride coated vanadium dioxide, which comprises a plurality of core-shell particles, the core-shell particles comprising a vanadium dioxide powder core and a calcium fluoride shell layer coated outside the vanadium dioxide powder.

[0035] By coating the vanadium dioxide powder with a calcium fluoride shell layer, the present application can effectively improve the visible light transmittance of the composite powder, while improving the solar light regulation ability, achieving high light transmittance and low heat absorption, that is, while ensuring good visual effect, it can intelligently control the entry of solar radiation heat, thereby maximizing the use of natural light and minimizing unnecessary heat gain / heat loss, achieving energy saving, comfort improvement and environmental benefits, etc. Multiple effects, suitable for application fields such as smart windows and optical coatings. In addition, the above-mentioned core-shell structure composite powder of calcium fluoride coated vanadium dioxide also has excellent thermal stability, excellent oxidation resistance, can effectively prolong its service life and has wide environmental applicability.

[0036] In some embodiments, the molar ratio of calcium to vanadium in the above-mentioned core-shell structure composite powder is (0.1-0.5):1. By adjusting the molar ratio of calcium to vanadium, the calcium fluoride shell layer is uniformly coated outside the vanadium dioxide powder, forming a calcium fluoride shell layer with appropriate thickness, which synergistically improves the visible light transmittance and solar light regulation ability of the composite powder.

[0037] In some embodiments, the above-mentioned vanadium dioxide powder is spherical or approximately spherical, and the particle size is ≤100 nm.

[0038] In some embodiments, the thickness of the calcium fluoride shell is 8-20 nm.

[0039] In some embodiments, the vanadium dioxide powder is a monoclinic vanadium dioxide powder (i.e., M-phase VO2 powder).

[0040] In another aspect, the application also provides a method for preparing the core-shell structure composite powder of calcium fluoride coated vanadium dioxide as described above, which comprises the following steps as shown in the figure: Figure 1 S1. uniformly mixing vanadium dioxide powder and a surfactant in a polar solvent to obtain a vanadium dioxide powder dispersion; S2. uniformly mixing a water-soluble calcium salt and the vanadium dioxide powder dispersion, then adding a water-soluble fluoride to perform a co-precipitation reaction, generating a calcium fluoride precipitate on the surface of the vanadium dioxide powder, then standing and aging to allow the calcium fluoride precipitate to coat and form an initial calcium fluoride shell on the surface of the vanadium dioxide powder; S3. collecting the reaction precipitate, washing and drying, then performing annealing treatment under a protective atmosphere to obtain the core-shell structure composite powder of calcium fluoride coated vanadium dioxide.

[0041] In some embodiments, in step S1, the surfactant comprises a non-ionic surfactant and / or an anionic surfactant. The non-ionic surfactant includes but is not limited to polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), etc.; the anionic surfactant includes but is not limited to a non-ionic surfactant such as a benzene bis-acid salt, etc. In some embodiments, the amount of the surfactant is 5-10 wt% of the total mass of the vanadium dioxide powder.

[0042] In some embodiments, in step S1, the polar solvent is selected from one or more of water, anhydrous ethanol, ethylene glycol, isopropyl alcohol, acetone, butanone, etc.

[0043] It can be understood that the source of the vanadium dioxide powder is not particularly limited in the application and can be commercially available or prepared by a method known to those skilled in the art, such as a one-step hydrothermal method.

[0044] In some embodiments, the method for preparing the vanadium dioxide powder comprises the following steps: uniformly mixing ammonium metavanadate and hydrazine monohydrochloride in a molar ratio of (2-3):1 in deionized water, then adding hydrochloric acid dropwise until the solution is blue and transparent, then adding ammonia water as a settling agent and adjusting the pH of the system to 7-8, collecting the brownish yellow soil precipitate, ultrasonically dispersing it in deionized water, and performing hydrothermal reaction in a reaction kettle at 210-280°C for 18-30h, then centrifuging, washing, and vacuum drying to obtain the vanadium dioxide powder. ​

[0045] In some embodiments, to enable the coprecipitation reaction to proceed more gently, the reaction is sufficient, the above water-soluble calcium salt, water-soluble fluoride can be dissolved in a solvent respectively to prepare water-soluble calcium salt solution, water-soluble fluoride solution, and then the water-soluble calcium salt solution and the above vanadium dioxide powder dispersion liquid are mixed uniformly, and then the water-soluble fluoride solution is added. The concentration of the water-soluble calcium salt solution and the water-soluble fluoride solution is not specially limited in the present application.

[0046] In some embodiments, in step S2, the above water-soluble calcium salt is selected from one or more of calcium chloride (CaCl2), calcium acetate (Ca(CH3COO)3), calcium nitrate (Ca(NO3)2), and calcium nitrate hydrate. The calcium nitrate hydrate includes calcium nitrate monohydrate (Ca(NO3)2·H2O), calcium nitrate tetrahydrate (Ca(NO3)2·4H2O), etc.

[0047] In some embodiments, in step S2, the above water-soluble fluoride is selected from one or more of potassium fluoride (KF), potassium fluoride hydrate (KF·2H2O), sodium fluoride (NaF), sodium fluoride hydrate (NaF·2H2O), and ammonium fluoride (NH4F).

[0048] In some embodiments, in step S2, the molar ratio of the above water-soluble calcium salt to the above vanadium dioxide powder is (0.1-0.5):1, and the molar ratio of the above water-soluble calcium salt to the above water-soluble fluoride is 1:(2-3). The above conditions can form a uniform calcium fluoride shell layer on the surface of the vanadium dioxide powder through the coprecipitation reaction, so that the coating effect of the calcium fluoride is good, the thickness is uniform, the dispersibility and stability of the core-shell structure composite powder of the calcium fluoride coated vanadium dioxide are improved, the phenomenon of oxidation of the vanadium dioxide core caused by the rupture of the calcium fluoride shell layer during the use of the core-shell structure composite material can be effectively avoided, and the visible light transmittance of the composite powder and the solar light regulation capability can be effectively improved.

[0049] In some embodiments, in step S2, the temperature of the above coprecipitation reaction is 50-70°C, and the time of the coprecipitation reaction is 100-150 min.

[0050] In some embodiments, in step S2, the temperature of the above standing and aging is 20-30°C, and the time of the standing and aging is 10-15 h.

[0051] In some embodiments, in step S3, the above protective atmosphere is selected from one or more of nitrogen, argon, neon, helium, xenon, or krypton.

[0052] In some embodiments, in step S3, the temperature of the above annealing treatment is 450-500°C, and the time of the annealing treatment is 2-4 h.

[0053] In another aspect, the present application also provides a temperature control coating, which comprises the core-shell structure composite powder and an additive.

[0054] In some embodiments, the additive comprises one or more of an organic solvent, a film-forming agent, a binder, and a leveling agent. The organic solvent comprises, but is not limited to, anhydrous ethanol, isopropyl alcohol, ethyl acetate, acetone, etc., which can disperse the powder to promote the mixing of the components and form a coating system that can be coated. The binder can be an organic polymer resin, such as, but not limited to, epoxy resin, phenolic resin, polyimide resin, etc. The leveling agent comprises, but is not limited to, one or a mixture of two of isophorone, diacetone alcohol, and butyl cellulose, which can promote the formation of a smooth, smooth, and uniform coating film during the drying and film-forming process, reduce the surface tension of the coating, and improve the leveling and uniformity. In actual applications, the skilled person in the art can also add other types of additives according to the special needs of different application scenarios, for example, to improve the heat insulation effect of the film, add infrared radiation powder as an additive, and reduce the temperature of the film surface through infrared reflection, which are all within the scope of the present application.

[0055] Based on this, the present application also provides an intelligent temperature control film, which is formed by applying the above-mentioned temperature control coating to the surface of a substrate and then drying.

[0056] The present application does not limit the method of "application", such as, but not limited to, coating, brushing, dipping, spraying, rolling, knife coating, flow coating, pouring, etc. The skilled person in the art can apply the above-mentioned temperature control coating to any substrate to prepare a temperature control film, and the substrate comprises, but is not limited to, architectural glass, automotive glass, plastic substrate, or a combination thereof.

[0057] The above technical solutions are described in detail in combination with specific embodiments. It should be understood that materials similar to or the same as the types, models, qualities, properties, or functions of the reagents and instruments used in the following examples can be used to implement the present application. The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples can be obtained from commercial sources unless otherwise specified.

[0058] The following are examples: Example 1 The calcium fluoride-coated vanadium dioxide composite powder preparation method provided in this embodiment comprises the following steps: The 5.0 g ammonium metavanadate was dissolved in 60 mL deionized water, and was stirred at 30 °C and 1500 r / min for 45 min to obtain a white ammonium metavanadate suspension. 1.0 g hydrazine monohydrochloride was completely dissolved in 10 mL deionized water to obtain a hydrazine monohydrochloride aqueous solution. The hydrazine monohydrochloride aqueous solution was added dropwise into the ammonium metavanadate suspension and was stirred uniformly, and the mixture was brown yellow. Then 15 mL concentrated hydrochloric acid was added dropwise, and the mixture changed from brown yellow to gray green, and a large amount of bubbles were generated during the process, until the mixture changed to a blue transparent solution. Then 20 mL ammonia was added dropwise as a precipitant, and the pH of the reaction system was adjusted to about 8.5. After centrifugation and washing, a brownish yellow precipitate was obtained. The brownish yellow precipitate was transferred into the PPL reactor liner of a metal reactor, and an appropriate amount of ultrapure water was added, and was ultrasonically mixed to enhance the dispersibility of the precipitate particles, to obtain a precursor suspension. Then the hydrothermal reaction was carried out at a temperature of 275 °C for 24 h. After cooling to room temperature, the black reaction product was taken out and was washed with deionized water, ethanol and isopropanol by centrifugation for 2 times, and was vacuum dried at 80 °C for 6 h, and was fully ground to obtain a nano VO2 powder.

[0059] The properties of the nano VO2 powder were characterized by Figure 2 (XRD pattern), which showed that the nano VO2 particles corresponded to the (011), (200) and (220) crystal planes of the standard card (JCPDS No. 82-0661) at 27.8°, 37.0° and 55.5°, respectively, and the M-phase nano VO2 powder was successfully prepared. Figure 3 The (a) SEM image showed that the nano VO2 powder was approximately spherical, and was easy to agglomerate. Figure 3 The (b) particle size distribution column chart showed that the particle size of the nano VO2 powder was 30 nm to 95 nm.

[0060] S1, 0.4 g of the above nano VO2 powder and 80 mL deionized water were stirred and mixed in a round-bottom flask for 8 h, and the powder was ultrasonically treated for 0.5 h every 2 h to enhance the dispersibility of the powder. Then 0.04 g of a surfactant polyvinylpyrrolidone (PVP) was added and was stirred and mixed for 8 h to obtain a nano VO2 powder dispersion.

[0061] S2, different amounts of water-soluble divalent inorganic calcium salt Ca(NO3)2·4H2O were weighed according to the molar ratio of calcium to vanadium of 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, and completely dissolved in 10 mL of deionized water to form a calcium salt aqueous solution. Metal fluoride salt KF·2H2O was weighed according to the molar ratio of calcium to fluorine of 1:2 and completely dissolved in 10 mL of deionized water to form a metal fluoride salt aqueous solution. The above calcium salt aqueous solution was added to the above nano-VO2 powder dispersion, and the pH of the reaction system was adjusted to 8.0 using ammonia water as a pH adjuster. Then, the round-bottom flask was placed on a heating magnetic stirrer and stirred at 60°C and 1500 r / min. At the same time, the above metal fluoride salt aqueous solution was slowly added to the reaction system at a speed of 0.1 mL / min. CaF2precipitate was generated on the surface of the nano-VO2 powder through a co-precipitation reaction. Then, the generated CaF2precipitate was aged for 12 h at room temperature to uniformly coat the nano-VO2 powder surface and form a preliminary CaF2coating layer. The coated composite powder was obtained.

[0062] S3, the black precipitate was collected, washed with deionized water and ethanol by alternating centrifugation 4 times, and then placed in a vacuum drying oven at 80°C for 6 h. Then, the temperature was raised to 480°C at a speed of 5°C / min in a vacuum tube furnace, and annealing treatment was performed under a nitrogen atmosphere for 3 h. Then, the calcium fluoride-coated vanadium dioxide composite powder with a core-shell structure (referred to as VO2@CaF2composite powder) was obtained by cooling. When the molar ratio of calcium to vanadium is 0.1:1, 0.2:1, 0.3:1, 0.4:1, and 0.5:1, the VO2@CaF2composite powder prepared is referred to as VO2@CaF2composite powder S1, S2, S3, S4, and S5, respectively.

[0063] The above series of VO2@CaF2composite powders were analyzed by XRD. Figure 4 It can be seen that the above composite powder corresponds to the (111), (220), and (311) crystal planes of the standard card (JCPDS No. 88-2301) at 28.2°, 47.0°, and 55.7°, respectively. The characteristic peaks corresponding to CaF2in the composite powder increase significantly as the molar ratio of calcium to vanadium increases, indicating that the VO2@CaF2composite powder is successfully prepared in this embodiment.

[0064] The surface microstructure of the VO2@CaF2composite powder was analyzed by SEM. Figure 5 Content (a) and Figure 5As can be seen from the SEM images at different scales in content (b), the VO2@CaF2 composite powder (composite powder S4) prepared in this embodiment is approximately spherical with good particle dispersion and no obvious agglomeration, which lays a good foundation for the subsequent preparation of intelligent temperature-controlled films with excellent optical performance and good uniformity.

[0065] Example 2 The method for preparing calcium fluoride-coated vanadium dioxide composite powder provided in this embodiment includes the following steps: S1. Mix 0.4g of the nano-VO2 powder prepared in Example 1 and 80mL of deionized water in a round-bottom flask for 12h. During this period, sonicate for 0.5h every 2h to enhance the dispersibility of the powder. Then add 0.04g of surfactant polyvinylpyrrolidone (PVP) and mix for 8h to obtain nano-VO2 powder dispersion.

[0066] S2. Weigh out different amounts of water-soluble divalent calcium salt CaCl2 according to the molar ratio of calcium to vanadium of 0.1:1, 0.18:1, 0.26:1, 0.34:1, 0.42:1, and 0.5:1, and completely dissolve them in 10 mL of deionized water to form an aqueous solution of calcium salt. Weigh out the metal fluoride salt NaF according to the molar ratio of calcium to fluoride of 1:2 and completely dissolve it in 10 mL of deionized water to form an aqueous solution of metal fluoride salt. The above-mentioned calcium salt aqueous solution was added to the above-mentioned nano-VO2 powder dispersion, and the pH of the reaction system was adjusted to 8.0 using ammonia water as a pH adjuster. Then, the round-bottom flask was placed on a heated magnetic stirrer and magnetically stirred at 60°C and 1500 r / min. At the same time, the above-mentioned metal fluoride salt aqueous solution was slowly added dropwise to the reaction system at a rate of 0.1 mL / min. CaF2 precipitate was generated on the surface of nano-VO2 powder through co-precipitation reaction. Then, the mixture was allowed to stand at room temperature for 12 h to allow the generated CaF2 precipitate to age and uniformly coat the surface of nano-VO2 powder to form a preliminary CaF2 coating layer.

[0067] S3. Collect the black precipitate, wash it four times with alternating centrifugation using deionized water and ethanol, and then dry it in a vacuum drying oven at 80℃ for 6 hours. Next, anneal it in a vacuum tube furnace at a rate of 5℃ / min to 480℃ under a nitrogen atmosphere for 3 hours. After cooling, obtain calcium fluoride-coated vanadium dioxide composite powder with a core-shell structure. The molar ratios of calcium to vanadium of 0.1:1, 0.18:1, 0.26:1, 0.34:1, 0.42:1, and 0.5:1 correspond to composite powders S1', S2', S3', S4', S5', and S6', respectively.

[0068] XRD analysis was performed on the above series of VO2@CaF2 composite powders. Figure 6It can be seen that the composite powder corresponds to the (111), (220), and (311) crystal planes of the standard card (JCPDS No. 88-2301) at 28.2°, 47.0°, and 55.7°, respectively. As the molar ratio of calcium to vanadium increases, the characteristic peak corresponding to CaF2 in the VO2@CaF2 composite powder increases significantly, indicating that VO2@CaF2 composite powder can also be prepared by using different water-soluble divalent calcium salts and metal fluoride salts.

[0069] TEM tests were performed on the above series of VO2@CaF2 composite powders. Figure 7 It can be seen that the CaF2 coating in the VO2@CaF2 composite powder is uniform, and the CaF2 coating thickness increases with the increase of the molar ratio of calcium to vanadium.

[0070] The surface microstructure of VO2@CaF2 composite powder was analyzed. Figure 8 Content (a) and Figure 8 As can be seen from the SEM images at different scales in content (b), the VO2@CaF2 composite powder (composite powder S5') prepared in this embodiment is approximately spherical, with good particle dispersion and no obvious agglomeration.

[0071] Elemental analysis was performed on the VO2@CaF2 composite powder. Figure 9 The EDS spectrum of VO2@CaF2 composite powder S5' shows that V and O elements are highly concentrated in the central region of the particles, while F and Ca elements are highly concentrated outside the core and on the entire surface. This indicates that the composite powder is a core-shell structure powder with VO2 as the core and CaF2 as the coating layer.

[0072] Application examples This application example provides a series of smart temperature-controlled films based on VO2@CaF2 composite powders from Examples 1 and 2. The preparation method of the smart temperature-controlled film includes the following steps: (1) Preparation of temperature-controlled coating A series of VO2@CaF2 composite powders (S1~S5, S1'~S6') prepared in Examples 1 and 2 were magnetically stirred with film-forming agent polyvinylpyrrolidone (PVP) and solvent anhydrous ethanol at 2000 r / min for 24 h to obtain a series of uniformly mixed temperature-controlled coatings (corresponding to A1~A5, A1'~A6' in sequence). The mass ratio of VO2@CaF2 composite powder to film-forming agent was 1:1, and the weight percentage of VO2@CaF2 composite powder in the temperature-controlled coatings was 3.38 wt%.

[0073] The nano-VO2 powder prepared in Example 1 was used as a control group and stirred with film-forming agent PVP and anhydrous ethanol at 2000 r / min under magnetic stirring for 24 h to obtain a well-mixed control coating A0. The mass ratio of nano-VO2 powder to film-forming agent was 1:1, the weight percentage of nano-VO2 powder in the control coating was 3.38 wt%, and the amount of VO2 used was consistent with the effective amount of VO2 in temperature-controlled slurry A5.

[0074] In addition, a VO2@CaF2 composite powder with a calcium to vanadium molar ratio of 0.7:1 was prepared according to the method provided in Example 2, and the composite powder was made into a control slurry A0' with a weight percentage of 3.38 wt% of VO2@CaF2 composite powder according to the preparation method of temperature control coatings A1' to A6'.

[0075] (2) Preparation of temperature-controlled thin film The above series of temperature-controlling coatings were uniformly coated on a silicon oxide substrate and placed on a heating plate at 75°C for 2 minutes to dry the solvent (anhydrous ethanol) to obtain a smart temperature-controlling coating. Then, the coating was spin-coated once and the solvent was dried to obtain a smart temperature-controlling film.

[0076] The control coating was uniformly coated onto a silicon oxide substrate using the above method to prepare a control film.

[0077] Figure 10 Content (a), Figure 10 Content (b) shows actual images of the control coating A0 prepared based on nano VO2 powder and the temperature-controlling coatings A1'~A6' prepared based on a series of VO2@CaF2 composite powders from Example 2, as well as actual images of the temperature-controlling films. It can be seen that the intelligent temperature-controlling film prepared based on VO2@CaF2 composite powder is more transparent than the simple VO2 film.

[0078] The optical properties and antioxidant properties of the intelligent temperature-controlling films prepared using the above-mentioned temperature-controlling coatings A1~A5 and A1'~A6', as well as the control films prepared using control coatings A0 and A0', were tested using the following methods: (a) Optical performance The test was conducted using an ultraviolet spectrophotometer, and the visible light transmittance was measured. T lum ), solar light modulation capability (Δ T sol The optical performance of the intelligent temperature-controlled thin film was evaluated. T lum Δ represents the transmittance of visible light in the wavelength range of 300~780nm. T sol Δ represents the ability of a thin film to regulate the amount of solar radiation (380~2500nm) entering a room in response to sunlight stimulation.T sol A higher value indicates a stronger ability of the thin film to modulate sunlight at high and low temperatures, and better heat insulation performance. The calculation formula is as follows:

[0079]

[0080]

[0081] in, φ lum The curve representing the relationship between photosensitivity and wavelength. T(λ) For wavelength in λ Transmittance at that location φ sol This represents the solar irradiance spectrum when the angle of incidence between sunlight and the horizon is 37° and the AM index is 1.5. T sol,l The solar transmittance of the thin film at 20°C. T sol,h This represents the solar transmittance of the thin film at 90°C. Optical performance test results are shown below. Figure 11 See Table 1.

[0082] (b) Antioxidant properties The intelligent temperature-controlling films prepared using the aforementioned temperature-controlling coatings A1 to A5, and the control film prepared using the aforementioned control coating A0, were exposed to air and heated at 300°C for 0 h, 2 h, 3 h, 4 h, 5 h, and 6 h to conduct antioxidant performance tests. The antioxidant performance test results are shown below. Figure 12 .

[0083] Table 1 Optical properties of intelligent temperature-controlling films prepared from temperature-controlling coatings A1~A5 and A1'~A6'

[0084] Depend on Figure 11As shown in Table 1, compared to the simple VO2 film prepared using the control slurry A0 (using nano-VO2 powder), the temperature-controlling films prepared using the temperature-controlling coatings A1~A5 and A1'~A6' provided in this application (using VO2@CaF2 composite powder) exhibit high visible light transmittance and strong solar light modulation capability. This indicates that the calcium fluoride-coated vanadium dioxide composite powder with a core-shell structure, prepared by coating calcium fluoride on the surface of vanadium dioxide, possesses excellent optical properties and can improve both the visible light transmittance and solar light modulation capability of the intelligent temperature-controlling film. Further experiments revealed that the visible light transmittance of the temperature-controlling film prepared using the control slurry A0' (the molar ratio of calcium to vanadium in the VO2@CaF2 composite powder is 0.7:1) decreased slightly, and the solar light modulation capability deteriorated significantly, making it unsuitable for preparing intelligent temperature-controlling films.

[0085] Depend on Figure 12 It can be seen that the pure VO2 film prepared using the control slurry A0 (using nano VO2 powder) has poor antioxidant properties. It was completely oxidized and turned yellow after being exposed to air and heated at 300°C for 3 hours. However, the intelligent temperature-controlled film prepared using the temperature-controlled coating provided in this application (using VO2@CaF2 composite powder) did not turn yellow after being exposed to air and heated at 300°C for 6 hours, and its antioxidant properties were excellent.

[0086] In summary, this application achieves superior optical performance by forming a uniformly thick CaF2 coating layer on the surface of nano-VO2 powder, which enhances both visible light transmittance and solar light modulation capability, thus preparing a VO2@CaF2 composite powder with a core-shell structure.

[0087] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A core-shell structured composite powder of calcium fluoride coated with vanadium dioxide, characterized in that, It contains multiple core-shell particles, the core-shell particles including a vanadium dioxide powder core and a calcium fluoride shell covering the vanadium dioxide powder.

2. The calcium fluoride-coated vanadium dioxide composite powder according to claim 1, characterized in that, In the core-shell composite powder, the molar ratio of calcium to vanadium is (0.1~0.5):

1.

3. The core-shell structured composite powder according to claim 1, characterized in that, The vanadium dioxide powder is spherical or nearly spherical, with a particle size ≤100nm; and / or, The thickness of the calcium fluoride shell is 8 nm to 20 nm.

4. The core-shell structured composite powder according to claim 1, characterized in that, The vanadium dioxide powder is a monoclinic phase vanadium dioxide powder.

5. A method for preparing a core-shell structured composite powder according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Vanadium dioxide powder and surfactant are mixed evenly in a polar solvent to obtain a vanadium dioxide powder dispersion. S2. Mix the water-soluble calcium salt and the vanadium dioxide powder dispersion, then add water-soluble fluoride to carry out a co-precipitation reaction, generate calcium fluoride precipitate on the surface of vanadium dioxide powder, and then let it stand for aging, so that the calcium fluoride precipitate coats the surface of vanadium dioxide powder and forms an initial calcium fluoride shell. S3. Collect the reaction precipitate, wash and dry it, and then anneal it under a protective atmosphere to obtain the core-shell structured composite powder of calcium fluoride coated vanadium dioxide.

6. The preparation method according to claim 5, characterized in that, In step S1, the surfactant includes nonionic surfactants and / or anionic surfactants; and / or, The polar solvent includes one or more of deionized water, anhydrous ethanol, ethylene glycol, isopropanol, acetone, and butanone; and / or, The amount of surfactant used is 5wt% to 15wt% of the total mass of the vanadium dioxide powder.

7. The preparation method according to claim 5, characterized in that, The vanadium dioxide powder is prepared by a one-step hydrothermal method, comprising the following steps: ammonium metavanadate and hydrazine monohydrochloride are mixed in deionized water at a molar ratio of (2~3):1, and then hydrochloric acid is added dropwise until the solution turns blue and transparent. Then, ammonia water is added dropwise as a precipitant and the pH of the system is adjusted to 7~8. A brownish-yellow precipitate is collected and ultrasonically dispersed in deionized water. The precipitate is then reacted in a reaction vessel at 210℃~280℃ for 18h~30h for hydrothermal reaction. After centrifugation, washing, and vacuum drying, the vanadium dioxide powder is obtained.

8. The preparation method according to claim 5, characterized in that, In step S2, the water-soluble calcium salt is selected from one or more of calcium chloride, calcium acetate, calcium nitrate, and calcium nitrate hydrate; and / or, The water-soluble fluoride is selected from one or more of potassium fluoride, potassium fluoride hydrate, sodium fluoride, sodium fluoride hydrate, and ammonium fluoride; and / or, The molar ratio of the water-soluble calcium salt to the vanadium dioxide powder is (0.1~0.5):1; and / or, The molar ratio of the water-soluble calcium salt to the water-soluble fluoride is 1:(2~3); and / or, The coprecipitation reaction is carried out at a temperature of 50℃~70℃ for a time of 100min~150min; and / or, The static aging temperature is 20℃~30℃, and the static aging time is 10h~15h; and / or, In step S3, the protective atmosphere is selected from one or more of nitrogen, argon, neon, helium, xenon, or krypton; and / or, The annealing temperature is 450℃~500℃, and the annealing time is 2h~4h.

9. A temperature-controlling coating, characterized in that, Includes the core-shell structured composite powder and additives as described in any one of claims 1 to 4; The additives include one or more of organic solvents, film-forming agents, binders, and leveling agents.

10. A smart temperature-controlled film, characterized in that, It is formed by applying the temperature-controlling coating of claim 9 to the surface of a substrate and then drying it; The substrate includes architectural glass, automotive glass, plastic substrates, or combinations thereof.

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