Method for large-scale preparation of monoclinic phase vanadium dioxide nano-powder, heat insulation film and application of heat insulation film

Abstract

The invention belongs to the field of functional nano materials, and relates to a method for large-scale preparation of monoclinic phase vanadium dioxide nano powder, a heat insulation film and application of the heat insulation film, and large-scale preparation of the monoclinic phase vanadium dioxide nano powder is successfully achieved by combining a coprecipitation method with low-temperature calcination. The obtained product has excellent size uniformity (the average particle size is 65 + / -10 nm) and an adjustable phase change characteristic (61-68 DEG C). The polymer-based composite film prepared based on the nano powder shows excellent optical performance, and the method has the advantages of mild reaction conditions (less than or equal to 600 DEG C), controllable product morphology and phase transition temperature and the like, and provides a reliable solution for industrial production of nano functional materials for intelligent windows.

Description

Technical Field

[0001] This invention belongs to the field of functional nanomaterials and relates to the preparation and application of vanadium dioxide nanopowder. Background Technology

[0002] Vanadium dioxide (VO2), a typical thermochromic material, undergoes a reversible metal-insulator phase transition (MIT) at a phase transition temperature close to room temperature (~68 °C). In the low-temperature phase (M phase, monoclinic crystal system), VO2 exhibits semiconductor properties with high transmittance to visible light; while in the high-temperature phase (R phase, rutile structure), it transforms into a metallic state, exhibiting strong reflectivity to near-infrared light. This self-responsive and reversible metal-insulator phase transition behavior, requiring no external energy, makes it an ideal choice for thermochromic materials used in smart windows.

[0003] VO2, as an amphoteric oxide, exists in various crystal forms, including monoclinic VO2 (M), orthorhombic VO2 (B), tetragonal VO2 (A), orthorhombic VO2 (D), and rutile VO2 (R). These crystal phases can interconvert under different oxygen partial pressures and temperatures. Among them, only VO2 (M) and VO2 (R) can undergo a phase transition at 68 °C, close to ambient temperature. However, precisely controlling the oxidation state of VO2 and obtaining specific crystal forms remains extremely challenging.

[0004] The synthesis of VO2 mainly faces the following challenges:

[0005] 1) The multivalence state characteristic of vanadium (V 2+ V 3+ V 4+ V 5+ This leads to difficulties in controlling phase purity;

[0006] 2) The transformation conditions between different crystal forms are harsh;

[0007] 3) Precise control of phase transition temperature at the nanoscale is extremely challenging.

[0008] Currently, the main methods for preparing VO2(M) powder include wet chemical methods (such as hydrothermal synthesis and sol-gel method) and dry chemical methods (such as ball milling, thermal decomposition, and magnetron sputtering). For example, CN114702850A discloses a hydrothermal method for preparing nano-sized vanadium dioxide powder. Although the hydrothermal method can provide a uniform temperature field to obtain products with uniform particle size and morphology, it has disadvantages such as complex waste liquid treatment and the need for high-pressure equipment. The sol-gel method and pyrolysis method require precise control of the precursor structure and composition. Although the solid-phase ball milling method has a simple principle, it relies on the collision of grinding balls to induce phase transformation. However, the collision of grinding balls of different sizes may produce significant local temperature differences, leading to uneven reduction reaction and ultimately affecting the homogeneity and quality of the VO2 product. Generally, the liquid-phase method can obtain nanoparticles with uniform morphology, but high-temperature post-treatment is still required to improve the crystallinity of the material. However, the competition between kinetic and thermodynamic mechanisms during calcination requires precise control of reaction conditions to obtain the target phase and microstructure, and the yield is low, making large-scale preparation impossible. Therefore, developing scalable, environmentally friendly, and precisely controllable VO2(M) synthesis routes has become a key research direction for smart window materials. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention proposes a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, a heat-insulating film, and its applications.

[0010] The technical solution of this invention is implemented as follows:

[0011] This application innovatively proposes a synergistic preparation strategy of "double-drop co-precipitation-low-temperature calcination," achieving controllable preparation of VO2(M) nanoparticles by establishing a control mechanism of "molecular-level mixing-low-temperature crystallization-defect regulation." Using soluble vanadium salts as the vanadium source, this invention employs a double-drop co-precipitation method. By controlling the dropping rate of the vanadium salt solution and the precipitant, and adjusting the pH value of the system in real time, the problem of uneven particle size caused by local supersaturation in traditional methods is solved. Low-temperature calcination is used to achieve the conversion of the precursor to VO2(M). By precisely controlling the calcination temperature and atmosphere flow rate, the phase transition temperature is precisely controlled while maintaining the monoclinic phase structure. The final obtained kilogram-scale (≥1 kg) monoclinic VO2 nanoparticles have an average particle size of 65 ± 10 nm, and the phase transition temperature can be precisely controlled within the range of 61~68 ℃. They exhibit high crystallinity, high phase purity, and good batch stability.

[0012] Specifically, this application discloses a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, comprising the following steps:

[0013] (1) Using the double-drop co-precipitation method, soluble vanadium salt and precipitant are added dropwise to distilled water simultaneously, the pH value of the titration system is controlled, and the reaction is stirred. After the reaction is completed, the precipitate is filtered and washed to obtain the vanadium precursor.

[0014] (2) The precursor of step (1) is calcined in an inert atmosphere in stages to obtain monoclinic vanadium dioxide nanopowder.

[0015] Further, the soluble vanadium salt mentioned in step (1) is at least one of vanadium trichloride, vanadium acetylacetonate, vanadium oxysulfate, vanadium acetylacetonate, vanadium oxyoxalate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, sodium vanadate, sodium pyrovanadate, and vanadium oxychloride, preferably vanadium oxysulfate or sodium metavanadate. When the initial vanadium species is vanadium with a +5 or +3 valence (V 5+ or V 3+ When present, it needs to be reduced or oxidized to +4 valence vanadium (V) under certain conditions. 4+ The product of this application. In the embodiments of this application, vanadium oxysulfate is used as a raw material to demonstrate the feasibility of this scheme. Similarly, vanadium oxyacetylacetonate and vanadium oxyoxalate are both soluble vanadium oxysulfate and can achieve the scheme of this application; ammonium metavanadate is a vanadium salt with a +5 valence, which is converted from vanadium oxysulfate to +5 valence by 10% sulfuric acid solution and anhydrous Na2SO3. 5+ Restore to V 4+ These can be used as raw materials to carry out the reaction. Similarly, sodium metavanadate, potassium metavanadate, and sodium pyrovanadate can also achieve the present invention through the above method; vanadium trichloride + trivalent vanadium salt, after being reacted with dilute hydrochloric acid (1.2 mol / L) and hydrogen peroxide (mass concentration of 30%), causes vanadium to change from V to vanadium trivalent. 3+ Oxidized to V 4+ Similarly, the same principle can be applied to obtain vanadium salts with +4 valence from other +3 valence vanadium salts through oxidation.

[0016] The precipitant can be any one of ammonium carbonate, ammonium bicarbonate, urea, urea, etc., with urea being preferred; the ratio of the amount of vanadium in the soluble vanadium salt to the amount of hydroxide ions (OH-) in the precipitant is controlled between 1:2.0 and 4.0.

[0017] Further, the specific preparation process in step (1) is as follows: First, adjust the pH value of pure water to between 4.5 and 8.0, raise the temperature to 50-95 ℃, and then add the soluble vanadium salt and precipitant dropwise to the pure water respectively. By controlling the dropping rate of the soluble vanadium salt and precipitant, the entire reaction system is maintained at a pH between 4.5 and 8.0. During the double-drop process, the vanadium raw material must be completely added. The alkaline precipitant used in the double-drop process can be supplemented or left over. The mechanical stirring speed is 300-600 rpm, and the reaction time is 2-6 hours. After the reaction, filter, wash with distilled water, and dry in a vacuum oven at 50-70 ℃ to obtain the vanadium precursor.

[0018] Preferably, the coprecipitation reaction temperature is 80-90 ℃, the reaction system is maintained at pH 4.5-8.0, the mechanical stirring speed is 500 rpm, and the reaction time is 3-4 hours.

[0019] Further, in step (2), the vanadium precursor obtained by co-precipitation is calcined at low temperature to obtain monoclinic vanadium dioxide. Under the protection of inert gas such as argon, the gas flow rate is controlled at 200-400 mL / min, the temperature is increased to 200-350 ℃ at a rate of 60-600 ℃ / h, and held for 0.5-1.0 hours. Then, the temperature is increased to 400-600 ℃ (preferably 480-550 ℃) at a rate of 120-600 ℃ / h, and held at the target temperature for 0.5-2.0 hours. After natural cooling to room temperature, monoclinic vanadium dioxide can be obtained.

[0020] Preferably, by controlling the flow rate of inert gas (such as Ar) within the range of 200-400 mL / min during the calcination process, the phase transition temperature of the obtained monoclinic vanadium dioxide (VO2 (M)) can be precisely controlled to the target range of 61-68 ℃ (±0.5 ℃).

[0021] This is because experimental results show that the vanadium precursor prepared by co-precipitation in step (1) is tetravalent vanadium hydroxide (VO(OH)2). During subsequent calcination, the precursor decomposes and releases reducing gases (such as CO, as confirmed by TG-MS detection). These gases have a crucial impact on the oxygen vacancy concentration of the final product. Therefore, during calcination, controlling the gas flow rate can balance the residence time of reducing gases (such as CO) in the reaction chamber, thereby maintaining a reducing atmosphere and controlling the phase transition temperature of vanadium dioxide.

[0022] Furthermore, a monoclinic vanadium dioxide nanopowder prepared by the above method has the molecular formula VO2 and the average particle size of its primary particles is 65 ± 10 nm.

[0023] A heat-insulating film containing the above-mentioned monoclinic vanadium dioxide nanoparticles.

[0024] The aforementioned film also contains a polymer matrix or cesium tungsten bronze.

[0025] When monoclinic vanadium dioxide nanoparticles are combined with a polymer matrix (such as polyvinyl butyral, polyethylene, polymethyl methacrylate, polycarbonate, etc.), the mass fraction of the polymer matrix is ​​90-99.8% of the thermal insulation film composite material; the mass fraction of the vanadium dioxide nanoparticles is 0.1-5.0% of the thermal insulation film composite material. A high-performance transparent thermal insulation film can be prepared, which achieves a solar light modulation efficiency of ≥17% while maintaining a visible light transmittance of >65% at a wavelength of 680 nm, demonstrating the excellent solar energy regulation performance of the smart window material.

[0026] When monoclinic vanadium dioxide nanoparticles are mixed with cesium tungsten bronze (Cs) 0.32A high-performance transparent heat-insulating film can be prepared by compounding WO3 and then combining it with a polymer matrix, wherein the mass fraction of the polymer matrix is ​​90-99.8% of the heat-insulating film composite material; the mass fraction of vanadium dioxide nanopowder is 0.1-5.0% of the heat-insulating film composite material; and the mass fraction of cesium tungsten bronze is 0.1-5.0%. While maintaining a visible light transmittance of ≥60% at a wavelength of 680 nm, the near-infrared light blocking rate at 1500 nm is ≥80%, and the solar energy modulation efficiency is ≥8.4%.

[0027] The present invention has the following beneficial effects:

[0028] 1. Simplified preparation process. The double-drop co-precipitation method is used to achieve molecular-level mixing, which solves the problem of uneven particle size caused by local supersaturation in traditional methods. The process is simple and efficient, with low-temperature calcination at normal pressure, low equipment requirements, low energy consumption, and an aqueous reaction system, making it green and environmentally friendly and suitable for industrial production.

[0029] 2. Excellent product performance. By controlling the gas flow rate and calcination temperature during solid-state calcination, precise control over the phase transition temperature (61~68 ℃) and particle size (65 ±10 nm) can be achieved, resulting in good batch stability. The monoclinic VO2(M) has high purity and is free of impurities. The heat-insulating film composited with polyvinyl butyral exhibits a visible light transmittance of >65% at 680 nm and a solar modulation efficiency of ≥17%; while the composite film with cesium tungsten bronze shows a visible light transmittance of ≥60% at 680 nm, a near-infrared blocking rate of ≥80% at 1500 nm, and a solar modulation efficiency of ≥8.4%.

[0030] 3. The preparation process of this invention is carried out under normal pressure, requiring minimal equipment and is simple to operate; the aqueous reaction system is environmentally friendly, waste liquid treatment is simple, and it is suitable for industrial production; the product has high purity and excellent performance, meeting the requirements of smart window applications. This invention provides practical feasibility for the large-scale preparation of high-performance monoclinic phase VO2 materials. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in 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 based on these drawings without creative effort.

[0032] Figure 1 The image shows the XRD pattern of the vanadium precursor prepared in Example 1 of this invention.

[0033] Figure 2 This is a SEM image of the vanadium precursor prepared in Example 1 of the present invention.

[0034] Figure 3 This is a TG-MS image of the vanadium precursor prepared in Example 1 of the present invention.

[0035] Figure 4 The image shows the XRD pattern of vanadium dioxide prepared in Example 1 of this invention.

[0036] Figure 5 This is a SEM image of vanadium dioxide prepared in Example 1 of the present invention.

[0037] Figure 6 This is a DSC diagram of vanadium dioxide prepared in Example 1 of the present invention.

[0038] Figure 7 The image shows the XRD pattern of vanadium dioxide prepared in Example 2 of this invention.

[0039] Figure 8 This is a DSC diagram of vanadium dioxide prepared in Example 2 of the present invention.

[0040] Figure 9 This is a DSC diagram of vanadium dioxide prepared in Example 3 of the present invention.

[0041] Figure 10 This is a DSC diagram of vanadium dioxide prepared in Example 4 of the present invention.

[0042] Figure 11 This is a SEM image of a single batch of kilogram-level (≥1 kg) vanadium dioxide prepared in Example 5 of the present invention;

[0043] Figure 12 An optical photograph of 25 kg of vanadium dioxide prepared in Example 5 of this invention.

[0044] Figure 13 This is a TEM image of the vanadium dioxide nanodispersion prepared in Application Example 1 of this invention.

[0045] Figure 14 The transmittance spectrum of the vanadium dioxide-PVB composite film prepared in Application Example 1 of this invention is shown.

[0046] Figure 15 TEM image and particle size distribution of the cesium tungsten bronze nano-dispersion prepared in Example 2 of this invention.

[0047] Figure 16 The transmittance spectrum of the PVB composite film prepared by combining vanadium dioxide and cesium tungsten bronze in Application Example 2 of this invention is shown. Detailed Implementation

[0048] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0049] Unless otherwise specified, the experimental methods used in the following experimental examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0050] Example 1

[0051] This embodiment describes a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, comprising the following steps:

[0052] (1) Weigh 50.0 g of vanadium oxysulfate and dissolve it in 500 mL of distilled water. Then weigh 45.0 g of urea and dissolve it in 200 mL of distilled water. Stir until completely dissolved. Measure 250 mL of pure water and adjust its pH to 4.5. Raise the temperature to 90 °C. Then add the prepared vanadium oxysulfate and urea solutions dropwise to the pure water. By adjusting the dropping rate of vanadium oxysulfate and urea, the reaction system is maintained at a pH of 4.5 ± 0.5. The mechanical stirring rate is 500 rpm, and the reaction time is 4 hours. After the reaction, filter the solution and wash it with distilled water until the conductivity of the filtrate is 400 μS / cm. Dry the filtrate in a vacuum oven at 70 °C to obtain the vanadium precursor.

[0053] XRD pattern of the precursor is shown below Figure 1 As shown, it is consistent with the spectrum of standard card JCPDF#11-0209, and is a crystal structure of VO(OH)2. Figure 2 The SEM image of the precursor shows that it has a short rod-like morphology with a length of approximately 400 nm and a diameter of approximately 20 nm. The prepared precursor was then subjected to TG-MS analysis, and the results are as follows... Figure 3 As shown. Figure 3 A significant CO signal (28 AMU) was detected in the 300 ℃ to 400 ℃ range. This is due to the decomposition of organic matter formed by the hydrolysis or condensation reaction of urea during co-precipitation, a stage accompanied by approximately 3% mass loss. Simultaneously, a very weak CO2 signal was observed, indicating the presence of trace amounts of carbon oxides.

[0054] (2) The vanadium precursor prepared is placed in a tube furnace. Under the protection of argon inert gas, the gas flow rate is controlled at 300 mL / min. The temperature is increased to 350 °C at a rate of 100 °C / h and held at 350 °C for 1 hour. Then the temperature is increased to 550 °C at a rate of 300 °C / h and held for 1 hour. After cooling naturally to room temperature, the product vanadium dioxide can be obtained. Figure 4 The XRD pattern of the calcined product is consistent with the characteristic peaks of the standard card JCPDF#82-0661, indicating that it is monoclinic vanadium dioxide and there are no impurity phases. Figure 5 The SEM image of the product shows that the average particle size is mainly distributed at 110 nm. The phase transition temperature test results are as follows... Figure 6 As shown, the phase transition temperature of vanadium dioxide prepared by this method is 66.4 ℃.

[0055] Example 2

[0056] This embodiment describes a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, comprising the following steps:

[0057] (1) Dissolve 6.0 g of vanadium oxysulfate in 50 mL of distilled water. Then weigh 15.0 g of urea and dissolve it in 50 mL of distilled water, stirring until completely dissolved. Measure 150 mL of pure water, adjust its pH to 5.0, raise the temperature to 80 ℃, and then add the prepared vanadium oxysulfate and urea solutions dropwise to the pure water. By adjusting the dropping rates of vanadium oxysulfate and urea, the reaction system is maintained at pH 5.0 ± 0.5, the mechanical stirring rate is 300 rpm, and the reaction time is 3 hours. After the reaction, filter the solution, wash it with distilled water until the conductivity of the filtrate is 50 μS / cm, and dry it in a vacuum oven at 60 ℃ to obtain the vanadium precursor.

[0058] (2) The prepared vanadium precursor was placed in a tube furnace. Under argon conditions, the argon gas flow rate was controlled at 300 mL / min. The temperature was increased to 350 °C at a rate of 150 °C / h and held for 1 hour. Then, the temperature was increased to 600 °C at a rate of 600 °C / h and held for 1 hour. After that, it was naturally cooled to room temperature to obtain the product vanadium dioxide. Its XRD results showed that it was a monoclinic vanadium dioxide pure phase. Figure 7 DSC results showed that its phase transition temperature was 68.6 ℃. Figure 8 ).

[0059] Example 3

[0060] This embodiment describes a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, comprising the following steps:

[0061] (1) Weigh 25.0 g of vanadium oxysulfate and dissolve it in 200 mL of distilled water. Weigh 48.0 g of urea and dissolve it in 200 mL of distilled water. Stir until completely dissolved. Measure 250 mL of pure water and adjust its pH to 6.0. Raise the temperature to 60 °C. Then add the prepared vanadium oxysulfate and urea solutions dropwise to the pure water respectively, so that the reaction system is maintained at pH 6.0 ± 0.5. The mechanical stirring speed is 300 rpm and the reaction time is 3 hours. After the reaction, filter and wash with distilled water until the conductivity of the filtrate is 100 μS / cm. Dry in a vacuum oven at 60 °C to obtain the vanadium precursor.

[0062] (2) The prepared vanadium precursor was placed in a tube furnace. Under argon conditions, the gas flow rate was controlled at 250 mL / min, and the temperature was increased to 350 °C at a rate of 150 °C / h, held for 0.5 hours, and then increased to 550 °C at a rate of 600 °C / h, held for 1 hour, and then naturally cooled to room temperature to obtain monoclinic vanadium dioxide. DSC results showed that its phase transition temperature was 64.5 °C ( Figure 9 ).

[0063] Example 4

[0064] This embodiment describes a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, comprising the following steps:

[0065] (1) Weigh 65.2 g of vanadium oxysulfate and dissolve it in 200 mL of distilled water. Weigh 80.0 g of urea and dissolve it in 200 mL of distilled water. Stir until completely dissolved. Measure 250 mL of pure water and adjust its pH to 6.0. Raise the temperature to 60 °C. Then add the prepared vanadium oxysulfate and urea solutions dropwise to the pure water respectively, so that the reaction system is maintained at pH 6.0 ± 0.5. The mechanical stirring speed is 300 rpm and the reaction time is 3 hours. After the reaction, filter and wash with distilled water until the conductivity of the filtrate is 100 μS / cm. Dry in a vacuum oven at 60 °C to obtain the vanadium precursor.

[0066] (2) The vanadium precursor was placed in a tube furnace. Under argon conditions, the gas flow rate was changed to 200 mL / min, and the temperature was increased to 350 °C at a rate of 100 °C / h, held for 1 hour, and then increased to 550 °C at a rate of 300 °C / h, held for 1 hour, and then naturally cooled to room temperature to obtain monoclinic vanadium dioxide. DSC results showed that its phase transition temperature was 61.0 °C ( Figure 10 ).

[0067] Example 5

[0068] This embodiment describes a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, comprising the following steps:

[0069] (1) Weigh 2000 g of vanadium oxysulfate and dissolve it in 12 L of distilled water. Then weigh 3000 g of urea and dissolve it in 15 L of distilled water. Stir until completely dissolved. Measure 15 L of pure water and adjust its pH to 4.5 with dilute sulfuric acid. Raise the temperature to 90 °C and perform a double-drop reaction to maintain the pH of the reaction system between 4.5 ± 0.5 for 6 hours. After the reaction, filter the solution and wash it with distilled water until the conductivity of the filtrate is 500 μS / cm. Dry the solution in a vacuum oven at 60 °C to obtain the vanadium precursor.

[0070] (2) The vanadium precursor prepared is placed in a tube furnace. Under the protection of argon inert gas, the gas flow rate is controlled at 250 mL / min. The temperature is increased to 350 °C at a rate of 120 °C / h and held at 350 °C for 0.5 hours. Then the temperature is increased to 550 °C at a rate of 300 °C / h and held at 550 °C for 1 hour. The product vanadium dioxide is obtained by naturally cooling to room temperature. Figure 11 The image shows a SEM image of the monoclinic vanadium dioxide product. The inset shows that the average particle size of the vanadium dioxide particles is 65 ± 10 nm. Figure 12 An optical photograph of a 25 kg vanadium dioxide sample prepared using this method.

[0071] Example 6

[0072] This embodiment describes a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, comprising the following steps:

[0073] (1) Take 150 ml of a 10% sulfuric acid solution, add 17.6 g of ammonium metavanadate (NH4VO3), and add 9.6 g of Na2SO3. After the reaction is complete, the vanadium in the ammonium metavanadate will change from V to NH4VO3. 5+ Restore to V 4+ Weigh 30.0 g of methylurea and dissolve it in 150 mL of distilled water, stirring until completely dissolved. Then, measure 200 mL of pure water, adjust the pH to 4.5 with dilute sulfuric acid, raise the temperature to 90℃, and simultaneously add the prepared vanadium solution and urea solution dropwise to the pure water. Maintain the pH of the reaction system between 4.5 ± 0.5 by adjusting the dropping rate. Maintain the mechanical stirring rate at 300 rpm for 6 hours. After the reaction, filter the solution, wash with distilled water until the conductivity of the filtrate is 300 μS / cm, and dry it in a vacuum oven at 60℃ to obtain the vanadium precursor.

[0074] (2) The precursor was placed in a tube furnace and the gas flow rate was controlled at 300 mL / min under an argon atmosphere. The temperature was raised to 200 °C at a rate of 120 °C / h and held for 0.5 hours. Then the temperature was raised to 480 °C at a rate of 300 °C / h and held for 2 hours. The temperature was then naturally cooled to room temperature to obtain monoclinic vanadium dioxide.

[0075] Example 7

[0076] This embodiment describes a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, comprising the following steps:

[0077] (1) Weigh 13.5 g of vanadium oxychloride (VOCl3) and dissolve it in 100 mL of dilute sulfuric acid (5% by mass). Add a certain amount of sodium sulfite to reduce it to tetravalent vanadium. Then weigh 50.0 g of urea and dissolve it in 200 mL of distilled water. Stir until completely dissolved. Measure 180 mL of pure water and adjust its pH to 8.0. Raise the temperature to 50 °C. Add the above solution dropwise to the pure water to maintain the reaction system at a pH of 8.0 ± 0.5. Stir at 600 rpm for 2 hours. After the reaction, filter the solution and wash it with distilled water until the conductivity of the filtrate is 100 μS / cm. Dry the filtrate in a vacuum oven at 60 °C to obtain the vanadium precursor.

[0078] (2) The precursor was placed in a tube furnace and the gas flow rate was controlled at 400 mL / min under an argon atmosphere. The temperature was raised to 350 °C at a rate of 150 °C / h and held for 1 hour. Then the temperature was raised to 480 °C at a rate of 300 °C / h and held for 2 hours. The temperature was then naturally cooled to room temperature to obtain monoclinic vanadium dioxide.

[0079] Example 8

[0080] This embodiment describes a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, comprising the following steps:

[0081] (1) Weigh 40.0 g of vanadium trichloride and dissolve it in 250 mL of dilute hydrochloric acid (1.2 mol / L), then add 14 g of hydrogen peroxide (mass concentration of 30%) to dissolve the vanadium in the solution. 3+ Oxidized to V 4+ Weigh out 60.0 g of urea and dissolve it in 150 mL of distilled water, stirring until completely dissolved. Measure 200 mL of pure water, adjust its pH to 8.0, raise the temperature to 70 ℃, and add the above solution to the pure water dropwise, maintaining the reaction system at a pH of 8.0 ± 0.5. Maintain the mechanical stirring speed at 450 rpm for 6 hours. After the reaction, filter the solution, wash it with distilled water until the conductivity of the filtrate is below 200 μS / cm, and dry it in a vacuum oven at 60 ℃ to obtain the vanadium precursor.

[0082] (2) The precursor was placed in a tube furnace and the gas flow rate was controlled at 300 mL / min under an argon atmosphere. The temperature was raised to 350 °C at a rate of 100 °C / h and held for 1 hour. Then the temperature was raised to 450 °C at a rate of 100 °C / h and held for 4 hours. The temperature was then naturally cooled to room temperature to obtain monoclinic vanadium dioxide.

[0083] Example 9

[0084] This embodiment describes a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, comprising the following steps:

[0085] (1) Weigh 15.0 g of vanadium sulfate and 5.0 g of vanadium oxalate and dissolve them together in 150 mL of distilled water. Then weigh 30.0 g of urea and dissolve it in 100 mL of distilled water. Stir until completely dissolved. Measure 150 mL of pure water and adjust its pH to 6.0. Raise the temperature to 95 °C and add the above mixed solution dropwise to the pure water to maintain the reaction system at a pH of 6.0 ± 0.5. The mechanical stirring speed is 500 rpm and the reaction time is 3 hours. After the reaction, filter and wash with distilled water until the conductivity of the filtrate is 150 μS / cm. Dry in a vacuum oven at 60 °C to obtain the vanadium precursor.

[0086] (2) The precursor was placed in a tube furnace and the gas flow rate was controlled at 200 mL / min under an argon atmosphere. The temperature was first increased to 200 °C at 100 °C / h and held for 1 hour. Then the temperature was increased to 550 °C at 200 °C / h and held for 1 hour. The temperature was then naturally cooled to room temperature to obtain monoclinic vanadium dioxide.

[0087] Example 10

[0088] This embodiment describes a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, comprising the following steps:

[0089] (1) Weigh 50.0 g of vanadium oxysulfate and dissolve it in 250 mL of distilled water. Then weigh 50.0 g of urea and dissolve it in 200 mL of distilled water. Stir until completely dissolved. Measure 100 mL of pure water and adjust its pH to 8.0. Raise the temperature to 80℃ and react using a double drop method to maintain the pH of the system between 8.0 and 0.5. The mechanical stirring rate is 400 rpm and the reaction time is 6 hours. After the reaction, filter the solution and wash it with distilled water until the conductivity of the filtrate is 400 μS / cm. Dry the solution in a vacuum oven at 60℃ to obtain the vanadium precursor.

[0090] (2) The precursor is placed in a rotary furnace and the gas flow rate is controlled at 300 mL / min under an argon atmosphere. First, the temperature is raised to 250℃ at 100℃ / h and held for 1 hour. Then, the temperature is raised to 550℃ at 200℃ / h and held for 1 hour. The temperature is then naturally cooled to room temperature to obtain monoclinic vanadium dioxide.

[0091] Example 11

[0092] This embodiment describes a method for large-scale preparation of monoclinic vanadium dioxide nanopowder, comprising the following steps:

[0093] (1) Weigh 25.0 g of sodium vanadate and dissolve it in 200 mL of dilute sulfuric acid (concentration: ), then pass sulfur dioxide gas through it to cause vanadium to change from V 5+ Restore to V 4+ Weigh out 40.0 g of urea and dissolve it in 150 mL of distilled water, stirring until completely dissolved. Measure 100 mL of pure water, adjust its pH to 5.0, raise the temperature to 90 ℃, and add the above solution dropwise to the pure water to maintain the reaction system at a pH of 5.0 ± 0.5. Maintain the mechanical stirring rate at 500 rpm for 2 hours. After the reaction, filter, wash, and dry to obtain the vanadium precursor.

[0094] (2) The precursor was placed in a tube furnace and the gas flow rate was controlled at 250 mL / min under an argon atmosphere. The temperature was raised to 300 °C at a rate of 120 °C / h and held for 1 hour. Then the temperature was raised to 400 °C at a rate of 300 °C / h and held for 2 hours. The temperature was then naturally cooled to room temperature to obtain monoclinic vanadium dioxide.

[0095] Application Example 1

[0096] A method for preparing a VO2 / PVB heat-insulating film, comprising the following steps:

[0097] 5 g of the VO2 powder prepared in Example 1 was placed in a beaker, 3 g of BYK2001 dispersant was weighed, and 40 g of ethyl acetate was added. The mixture was stirred until fully mixed. The mixture was then ground using a nanomilling machine for 18 min to obtain a uniform and stable VO2 nano-dispersion slurry. Transmission electron microscopy characterized the particle size as below 35 nm. Figure 13 ).

[0098] 1.5 g of PVB powder was weighed and added to 13 g of anhydrous ethanol to obtain PVB colloid. Then, 0.15 g of triethylene glycol diisooctanoate and 0.04 g of the prepared VO2 nano-dispersion slurry (solid content 10.4%) were added and mixed thoroughly to obtain a film-forming solution. The film-forming solution was coated onto a glass substrate using a blade coating method and kept in an oven at 60 ℃ for 3 h to ensure the film was dry, resulting in a uniform and transparent VO2 / PVB heat-insulating film.

[0099] The transmittance of the thin film was measured at room temperature and 90 °C using a UV-Vis-NIR spectrophotometer. Figure 8 As shown, calculations show that when the visible light transmittance at 680 nm is 66.3%, the modulation efficiency of the thin film in the entire solar spectrum range of 250-2500 nm is 17.2%. Figure 14 ).

[0100] Application Example 2

[0101] A method for preparing a PVB heat-insulating film composed of vanadium dioxide and cesium tungsten bronze, comprising the following steps:

[0102] a. Take cesium tungsten bronze (Cs 0.32 9.6 g of WO3 powder was placed in a beaker, 20 g of BYK2001 dispersant was weighed out, and 30 g of ethyl acetate was added. The mixture was stirred until fully mixed. The mixture was then ground using a nano-grinding mill for 18 minutes to obtain a uniform and stable cesium tungsten bronze nano-dispersion slurry. The prepared cesium tungsten bronze nano-dispersion had the following particle size distribution: Figure 15 As shown, the average particle size is 39 nm.

[0103] b. Take 0.11 g of the VO2 nano-dispersion prepared in Example 1 (solid content of 2.2%) and mix it evenly with 0.05 g of the cesium tungsten bronze nano-dispersion (solid content of 2.8%). Then weigh 15 g of PVB colloid (solid content of 10.3%) and 0.15 g of triethylene glycol diisooctanoate, mix them evenly, and obtain a vanadium dioxide and cesium tungsten bronze composite PVB heat insulation film.

[0104] TEM image of VO2 nano-dispersion as shown Figure 13 As shown, by Figure 13 It can be seen that the vanadium dioxide particles are uniformly dispersed, with an average size of 35 nm.

[0105] The transmittance of the thin film was measured at room temperature and 100 °C using a UV-Vis-NIR spectrophotometer. Figure 16 As shown, calculations show that the visible light transmittance at 680 nm is 60.9%, the solar light modulation capability can reach 8.4%, and the near-infrared light shielding capability at 1500 nm is over 80%.

[0106] Application Example 3

[0107] A method for preparing a VO2 / PVB heat-insulating film, comprising the following steps:

[0108] 10 g of vanadium dioxide powder prepared in Example 10 was mixed with 12 g of BYK2001 dispersant and then ground for 15 minutes at 73 Hz using a nano-mill to obtain a VO2 nano-dispersion slurry. Separately, 10 g of PVB colloid (solid content 10.3%) was mixed with 0.1 g of triethylene glycol diisooctanoate and 0.025 g of the VO2 nano-dispersion slurry (solid content 18.9%) to prepare a film-forming solution. The film-forming solution was coated onto a glass substrate and dried at 60 ℃ for 3 hours. To obtain a uniform film, the dried VO2 / PVB composite film was placed in a 25 mm × 25 mm × 0.38 mm mold and hot-pressed using a hot press to finally obtain a uniform and transparent VO2 / PVB heat-insulating film.

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for large-scale preparation of monoclinic vanadium dioxide nanopowder, characterized in that, The steps are as follows: (1) Soluble vanadium salt and precipitant are added dropwise to distilled water at the same time, the pH value of the titration system is controlled, and the reaction is stirred. After the reaction is completed, the precipitate is filtered and washed to obtain the vanadium precursor. (2) The precursor of step (1) is calcined in an inert atmosphere in stages to obtain monoclinic vanadium dioxide nanopowder.

2. The method for large-scale preparation of monoclinic vanadium dioxide nanopowder according to claim 1, characterized in that: In step (1), the soluble vanadium salt is a +4 valence vanadium salt; the precipitant is selected from any one of ammonium carbonate, ammonium bicarbonate, urea and urea.

3. The method for large-scale preparation of monoclinic vanadium dioxide nanopowder according to claim 2, characterized in that: The +4 vanadium salt is selected from any one of vanadium oxysulfate, vanadium oxyacetylacetonate, or vanadium oxyoxalate, or a +4 vanadium salt obtained by oxidation or reduction of any one of vanadium trichloride, vanadium oxyacetylacetonate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, sodium vanadate, sodium pyrovanadate, and vanadium oxyacetylacetonate.

4. The method for large-scale preparation of monoclinic vanadium dioxide nanopowder according to claim 2, characterized in that: The ratio of the amount of vanadium in the soluble vanadium salt to the amount of hydroxide ions in the precipitant is controlled at 1:2.0-4.

0.

5. The method for large-scale preparation of monoclinic vanadium dioxide nanopowder according to any one of claims 1-4, characterized in that: The pH value is 4.5-8.0, the temperature of the stirring reaction is 50-95℃, the time is 2-6 hours, and the stirring rate is 300-600 rpm.

6. The method for large-scale preparation of monoclinic vanadium dioxide nanopowder according to claim 5, characterized in that: In step (2), the flow rate of the inert atmosphere is 200-400 mL / min; the heating rate of the first stage of the segmented calcination is 60-600℃ / h, heating to 200-350℃ and holding for 0.5-1.0 hours; the heating rate of the second stage is 120-600℃ / h, heating to 400-600℃ and holding for 0.5-2.0 hours.

7. The monoclinic vanadium dioxide nanopowder prepared by the method according to any one of claims 1-4 and 6, characterized in that: The average diameter of the monoclinic vanadium dioxide nanopowder is 65 ± 10 nm.

8. A heat-insulating film, characterized in that: The heat-insulating film contains the monoclinic vanadium dioxide nanoparticles as described in claim 7.

9. The heat-insulating film according to claim 8, characterized in that: The film also contains a polymer matrix and / or cesium tungsten bronze; The polymer matrix is ​​selected from any one of polyvinyl butyral, polyethylene, polymethyl methacrylate and polycarbonate.

10. The application of the heat-insulating film according to claim 8 or 9 in the preparation of smart window materials.

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