Antioxidant vanadium dioxide nano-powder and preparation method thereof

Abstract

The invention discloses antioxidant vanadium dioxide nano powder and a preparation method thereof. The method comprises the steps of preparation and surface modification of a core suspension, adsorption and in-situ growth of a shell precursor, solid-liquid separation and pretreatment, crystal form reconstruction, shell densification and the like. Tungsten-doped vanadium dioxide is adopted as a core, interface affinity is improved through a surface modifier, a high-temperature annealing process is combined, an inorganic shell layer (such as silicon dioxide) is induced to shrink and densify, and the nano powder with a core-shell structure is formed. The method effectively solves the problems that vanadium dioxide is easy to oxidize to lose a thermochromic function and is easy to agglomerate in a humid and hot environment, and the prepared powder has excellent weather resistance, dispersibility and appropriate phase transition temperature.

Description

Technical Field

[0001] This invention relates to the field of inorganic nanomaterials technology, specifically to a method for preparing tungsten-doped vanadium dioxide nanopowder with a core-shell structure, which is particularly suitable for preparing intelligent energy-saving window temperature control materials with long lifespan and high light transmittance. Background Technology

[0002] Vanadium dioxide (VO2) is a typical strongly correlated transition metal oxide with reversible metal-insulator (MIT) phase transition characteristics. When the temperature is below the phase transition temperature (approximately 68°C), it exists in the monoclinic phase (M phase), exhibiting a semiconductor state and high transmittance to infrared light. When the temperature is above the phase transition temperature, it transforms into the rutile phase (R phase), exhibiting a metallic state and high reflectivity to infrared light. This characteristic of automatically adjusting solar thermal radiation transmittance with temperature makes it a promising candidate for applications in the field of smart energy-saving windows.

[0003] However, the practical application of vanadium dioxide in commercial smart glass still faces numerous technical bottlenecks. First, the phase transition temperature of pure vanadium dioxide is approximately 68°C, far exceeding the human comfort temperature (20-25°C). It must be lowered to near room temperature through doping before practical application. Second, vanadium in vanadium dioxide, which has thermochromic properties, is in the +4 valence state, exhibiting poor thermodynamic stability. In air (especially in humid and hot environments), it is easily oxidized to the more stable +5 valence vanadium pentoxide. Vanadium pentoxide is a bright yellow color and lacks thermochromic properties, which will cause the smart window to discolor, degrade in performance, or even completely fail after a period of use. Furthermore, vanadium dioxide nanoparticles are prone to agglomeration, resulting in low visible light transmittance in the final product.

[0004] To address the aforementioned issues, existing technologies typically employ a core-shell structure formed by coating the surface of vanadium dioxide with an inert material (such as silicon dioxide) to isolate oxygen and moisture. However, current preparation methods often suffer from uneven coating and insufficient shell density, preventing the achievement of truly long-lasting oxidation resistance. Therefore, developing a process-controllable method for preparing antioxidant vanadium dioxide nanopowders that enables dense coating and simultaneous doping modification is a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing antioxidant vanadium dioxide nanopowder. This method improves interfacial affinity by introducing surface modifiers and combines a high-temperature annealing process to achieve core crystallization and shell densification, thereby preparing core-shell structured nanopowder with excellent antioxidant properties (weather resistance) and a suitable phase transition temperature.

[0006] To achieve the above object, the technical scheme adopted by the present invention is as follows: A preparation method of antioxidant vanadium dioxide nano powder, comprising the following steps: (1) Preparation and surface modification of the core suspension: Dispersing tungsten-doped vanadium dioxide nanoparticles or their precursor powders in an alcohol-water mixed solvent, adding a surface modifier, and through dispersion treatment, enabling the surface modifier to adsorb on the particle surface to obtain a modified core suspension; (2) Adsorption and in-situ growth of the shell precursor: Adding a shell source material to the modified core suspension, and adjusting the pH value of the system. Under stirring conditions, inducing hydrolysis and polycondensation reactions of the shell source material on the particle surface, and through aging treatment, forming particles with a pre-coated layer; (3) Solid-liquid separation and pretreatment: Separating the solid and liquid of the product obtained in step (2), washing, and drying in a vacuum or inert atmosphere to obtain a core-shell structure precursor powder; (4) Crystal structure reconstruction and shell densification: Placing the core-shell structure precursor powder in an inert atmosphere or a reducing atmosphere for high-temperature annealing treatment, improving the crystallinity of the core through heat treatment and inducing the shell to shrink and densify to obtain the antioxidant vanadium dioxide nano powder.

[0007] Among them, the prepared nano powder has a core-shell structure, the core is tungsten-doped vanadium dioxide, and the chemical general formula is W x V 1-x O2, where 0 < x ≤ 0.05; the shell is a dense inorganic barrier layer coated on the surface of the core.

[0008] Preferably, in step (1), the surface modifier is selected from one or more of polyvinylpyrrolidone, polyethylene glycol, silane coupling agent or cetyltrimethylammonium bromide; in the alcohol-water mixed solvent, the volume percentage of alcohol is 60% - 90%.

[0009] Preferably, in step (2), the shell source material is tetraethyl orthosilicate; adjusting the pH value of the system is to adjust the pH value to 8 - 11 using ammonia water; the temperature of the hydrolysis and polycondensation reaction is controlled at 25°C - 60°C, the reaction time is 2 - 6 hours, and the aging time is 1 - 12 hours.

[0010] Preferably, the specific parameters of the high-temperature annealing treatment in step (4) are: the atmosphere is high-purity argon, high-purity nitrogen or an argon-hydrogen mixed gas containing 5% by volume of hydrogen; the temperature is 400°C - 600°C; the holding time is 1 - 4 hours; the heating rate is 2°C / min - 10°C / min.

[0011] Preferably, the material of the shell is selected from a composite of one or more of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide or magnesium fluoride; more preferably, the shell is amorphous silicon dioxide.

[0012] Preferably, the microscopic geometric parameters of the nanoparticles prepared by the method meet the following ranges: the average particle size of the core is 20 nm to 100 nm; and the average thickness of the shell is 2 nm to 20 nm.

[0013] Preferably, the nanoparticles have excellent weather resistance; after being placed in an environment with a temperature of 60°C and a relative humidity of 90% for 30 days, the color of the powder does not change significantly and remains grayish-black.

[0014] Preferably, the tungsten doping amount x is in the range of 0.005 ≤ x ≤ 0.03, and the phase transition temperature of the nanopowder is adjustable in the range of 20℃ to 45℃.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. Excellent oxidation resistance: Through surface modification to induce uniform coating, combined with high-temperature annealing process, the shell shrinks and densifies, effectively eliminating shell defects and significantly blocking the penetration of oxygen and water vapor. This solves the problem of vanadium dioxide easily oxidizing and discoloring in humid and hot environments, and greatly extends the service life of the material.

[0016] 2. The process is controllable and the performance is adjustable. The process flow of the method of the present invention is clear. By adjusting the reaction parameters, the core particle size, shell thickness and phase transition temperature can be effectively controlled to meet the needs of different application scenarios. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the process flow for the preparation method of antioxidant vanadium dioxide nanopowder according to the present invention.

[0019] Figure 2 This is a comparison table of key performance indicators between the powders prepared in Examples 1-3 of the present invention and the powder in Comparative Example 1.

[0020] Figure 3 The X-ray diffraction (XRD) pattern of the powder prepared in Example 3 of this invention. Detailed Implementation

[0021] The specific embodiments of the present invention will be briefly described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] Example 1 (1) Preparation and surface modification of the nuclear suspension: 1.0 g of tungsten-doped vanadium dioxide precursor powder with an average particle size of approximately 30 nm (doping amount x = 0.01) was weighed and dispersed in 100 mL of an alcohol-water mixed solvent. The alcohol-water mixed solvent consisted of 60 mL of anhydrous ethanol and 40 mL of deionized water (alcohol volume ratio 60%). 0.1 g of polyvinylpyrrolidone (PVP K30) was added to the dispersion as a surface modifier. The mixture was placed in an ultrasonic cleaner and ultrasonically dispersed for 30 minutes to allow PVP to be fully adsorbed onto the particle surface, thus obtaining the modified nuclear suspension.

[0023] (2) Adsorption and in-situ growth of the shell precursor: The modified core suspension was placed on a magnetic stirrer, and the reaction temperature was controlled at 25°C. 0.5 mL of tetraethyl orthosilicate was added dropwise to the suspension as the shell source material. Subsequently, ammonia was slowly added dropwise to adjust the pH of the system to 8.0. The reaction was carried out for 6 hours under continuous stirring to allow the tetraethyl orthosilicate hydrolysis products to deposit on the core surface. After the reaction was completed, the mixture was allowed to stand for 12 hours to form particles with a pre-coated layer.

[0024] (3) Solid-liquid separation and pretreatment: The suspension obtained in step (2) was placed in a centrifuge and centrifuged at 8000 rpm for 10 minutes, and the supernatant was discarded. The precipitate was washed three times alternately with anhydrous ethanol and deionized water. The washed solid was placed in a vacuum drying oven and dried at 60°C for 12 hours to obtain the core-shell structure precursor powder.

[0025] (4) Crystal form reconstruction and shell densification: The dried precursor powder was placed in a tube furnace and high-purity argon gas (99.999% purity) was introduced as a protective atmosphere. The temperature was increased to 400℃ at a heating rate of 2℃ / min and held for 4 hours. The powder was then cooled to room temperature in the furnace to obtain antioxidant vanadium dioxide nanoparticles.

[0026] Example 2 (1) Preparation and surface modification of the nuclear suspension: 1.0 g of tungsten-doped vanadium dioxide precursor powder with an average particle size of approximately 50 nm (doping amount x = 0.02) was weighed and dispersed in 100 mL of an alcohol-water mixture. The alcohol-water mixture consisted of 75 mL of anhydrous ethanol and 25 mL of deionized water (alcohol volume ratio 75%). 0.3 g of polyvinylpyrrolidone (PVP K30) was added to the dispersion as a surface modifier. The mixture was placed in an ultrasonic cleaner and ultrasonically dispersed for 45 minutes to obtain the modified nuclear suspension.

[0027] (2) Adsorption and in-situ growth of the shell precursor: The modified core suspension was placed on a magnetic stirrer, and the reaction temperature was controlled at 45°C. 1.5 mL of tetraethyl orthosilicate was added dropwise to the suspension. Subsequently, ammonia was slowly added dropwise to adjust the pH of the system to 9.5. The reaction was carried out for 4 hours under continuous stirring. After the reaction was completed, the mixture was allowed to stand for 6 hours to form particles with a pre-coated layer.

[0028] (3) Solid-liquid separation and pretreatment: The suspension obtained in step (2) was placed in a centrifuge and centrifuged at 8000 rpm for 10 minutes, and the supernatant was discarded. The precipitate was washed three times alternately with anhydrous ethanol and deionized water. The washed solid was placed in a vacuum drying oven and dried at 80°C for 8 hours to obtain the core-shell structure precursor powder.

[0029] (4) Crystal form reconstruction and shell densification: The dried precursor powder was placed in a tube furnace and high-purity nitrogen was introduced as a protective atmosphere. The temperature was increased to 500℃ at a heating rate of 5℃ / min and held for 2 hours. The furnace was then cooled to room temperature to obtain antioxidant vanadium dioxide nanoparticles.

[0030] Example 3 (1) Preparation and surface modification of the nuclear suspension: 1.0 g of tungsten-doped vanadium dioxide precursor powder with an average particle size of approximately 80 nm (doping amount x = 0.03) was weighed and dispersed in 100 mL of an alcohol-water mixed solvent. The alcohol-water mixed solvent consisted of 90 mL of anhydrous ethanol and 10 mL of deionized water (alcohol volume ratio 90%). 0.5 g of silane coupling agent (KH-570) was added to the dispersion as a surface modifier. The mixture was placed in an ultrasonic cleaner and ultrasonically dispersed for 60 minutes to obtain the modified nuclear suspension.

[0031] (2) Adsorption and in-situ growth of the shell precursor: The modified core suspension was placed on a magnetic stirrer, and the reaction temperature was controlled at 60°C. 3.0 mL of tetraethyl orthosilicate was added dropwise to the suspension. Subsequently, ammonia was slowly added dropwise to adjust the pH of the system to 11.0. The reaction was carried out under continuous stirring for 2 hours. After the reaction was completed, the mixture was allowed to stand for 1 hour to form particles with a pre-coated layer.

[0032] (3) Solid-liquid separation and pretreatment: The suspension obtained in step (2) was placed in a centrifuge and centrifuged at 8000 rpm for 10 minutes, and the supernatant was discarded. The precipitate was washed three times alternately with anhydrous ethanol and deionized water. The washed solid was placed in a vacuum drying oven and dried at 80°C for 12 hours to obtain the core-shell structure precursor powder.

[0033] (4) Crystal form reconstruction and shell densification: The dried precursor powder was placed in a tube furnace, and an argon-hydrogen mixture (5% hydrogen + 95% argon) was introduced as a protective atmosphere. The temperature was increased to 600℃ at a heating rate of 10℃ / min and held for 1 hour. The powder was then cooled to room temperature in the furnace to obtain antioxidant vanadium dioxide nanoparticles.

[0034] Comparative Example 1 This comparative example prepared tungsten-doped vanadium dioxide powder without a shell to compare its antioxidant properties.

[0035] (1) Suspension preparation: Weigh 1.0 g of tungsten-doped vanadium dioxide precursor powder (doping amount x = 0.02, same as in Example 2), disperse it in 100 mL of alcohol-water mixed solvent, and do not perform surface modification treatment. (2) No coating treatment: The steps of adding tetraethyl orthosilicate and hydrolysis coating in the example are omitted. (3) Solid-liquid separation and pretreatment: The suspension is directly centrifuged, washed, and dried. (4) Crystal reconstruction: The dried powder is placed in a tube furnace and high-purity nitrogen is introduced. The temperature is increased to 500℃ at a heating rate of 5℃ / min and held for 2 hours. The furnace is cooled to room temperature to obtain tungsten-doped vanadium dioxide nanopowder without a shell.

[0036] The core-shell structured powders prepared in Examples 1-3 and the shell-less powder prepared in Comparative Example 1 were simultaneously placed in a constant temperature and humidity chamber (conditions: 60℃, relative humidity 90%) for accelerated aging tests for 30 days. The color changes were observed to evaluate the antioxidant properties. The phase transition temperature of each sample was also tested.

[0037] Test results show that the powders prepared in Examples 1-3 maintained their grayish-black color after aging tests, indicating that the dense shell effectively blocked oxidation. In contrast, the powder in Comparative Example 1 turned a bright yellow (characteristic color of vanadium pentoxide) after aging, indicating that it had completely oxidized and failed. For a comparison of the specific performance indicators of each sample, please refer to the appendix. Figure 2 Please refer to the appendix for the XRD pattern of the sample in Example 3. Figure 3 In summary, the vanadium dioxide powder prepared by the method of this invention exhibits excellent stability and antioxidant properties, making it highly suitable for large-scale industrial production.

[0038] In the description of this invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0039] The above description of the disclosed embodiments enables those skilled in the art to make and use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit and scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing antioxidant vanadium dioxide nanopowder, characterized in that, Includes the following steps: Step 1: Preparation and surface modification of nuclear suspension: Tungsten-doped vanadium dioxide nanoparticles or their precursor powder are dispersed in an alcohol-water mixed solvent, a surface modifier is added, and after dispersion treatment, the surface modifier is adsorbed on the particle surface to obtain a modified nuclear suspension. Step 2, Adsorption and in-situ growth of shell precursor: Add shell source material dropwise to the modified core suspension and adjust the pH value of the system. Under stirring conditions, induce the shell source material to undergo hydrolysis and condensation reaction on the particle surface. After aging treatment, form particles with pre-coated layer. Step 3, Solid-liquid separation and pretreatment: The product obtained in Step 2 is subjected to solid-liquid separation and washing, and then dried under vacuum or inert atmosphere to obtain core-shell structured precursor powder; Step 4. Crystal form reconstruction and shell densification: The core-shell structure precursor powder is placed in an inert atmosphere or a reducing atmosphere for high-temperature annealing treatment. By heat treatment, the crystallinity of the core is improved and the shell is induced to shrink and densify, obtaining an antioxidant vanadium dioxide nano powder; among them, the prepared nano powder has a core-shell structure, the core is tungsten-doped vanadium dioxide, and the chemical general formula is W x V 1-x O2, where 0 < x ≤ 0.05; the shell is a dense inorganic barrier layer coated on the surface of the core.

2. The method for preparing antioxidant vanadium dioxide nanopowder according to claim 1, characterized in that, In step one, the surface modifier is selected from one or more of polyvinylpyrrolidone, polyethylene glycol, silane coupling agent or hexadecyltrimethylammonium bromide; in the alcohol-water mixed solvent, the volume percentage of alcohol is 60% to 90%.

3. The method for preparing antioxidant vanadium dioxide nanopowder according to claim 1, characterized in that, In step two, the shell source material is tetraethyl orthosilicate; the pH value of the system is adjusted to 8-11 using ammonia; the temperature of the hydrolysis and condensation reaction is controlled at 25℃-60℃, the reaction time is 2-6 hours, and the aging time is 1-12 hours.

4. The method for preparing antioxidant vanadium dioxide nanopowder according to claim 1, characterized in that, The specific parameters for the high-temperature annealing treatment in step four are as follows: Atmosphere: high-purity argon, high-purity nitrogen, or an argon-hydrogen mixture containing 5% hydrogen by volume; Temperature: 400℃~600℃; Holding time: 1~4 hours; Heating rate: 2℃ / min~10℃ / min.

5. The method for preparing antioxidant vanadium dioxide nanopowder according to claim 1, characterized in that, The shell material is selected from one or more of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, or magnesium fluoride, or a composite thereof.

6. The method for preparing antioxidant vanadium dioxide nanopowder according to claim 1, characterized in that, The microscopic geometric parameters of the nanopowder prepared by the method meet the following ranges: the average particle size of the core is 20 nm to 100 nm; the average thickness of the shell is 2 nm to 20 nm; and the phase transition enthalpy decay rate measured by differential scanning calorimetry is less than 5% after the nanopowder is placed in an environment of 60°C and 90% relative humidity for 30 days.

7. The method for preparing antioxidant vanadium dioxide nanopowder according to claim 1, characterized in that, The tungsten doping amount x ranges from 0.005 ≤ x ≤ 0.03, and the phase transition temperature of the nanopowder is adjustable in the range of 20℃ to 45℃.

8. An antioxidant vanadium dioxide nanopowder prepared using the preparation method of antioxidant vanadium dioxide nanopowder according to any one of claims 1 to 7.

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