High-stability vanadium dioxide-based nanomaterial and preparation and application thereof

Abstract

The present application relates to VO2-based temperature control intelligent energy-saving material technical field, especially to a kind of high stability vanadium dioxide-based nanomaterial and its preparation and application.The present application first dissolves the composition of TEOS and MTES in solvent, obtains mixed solution A;Mixing acid catalyst, water and solvent, obtains mixed solution B;Then L-ascorbic acid is dissolved in VO2 dispersion, VO2 is pretreated;Mixed solution A and mixed solution B are added to the pretreated VO2 dispersion in parallel to carry out coating treatment, that is, high stability vanadium dioxide-based nanomaterial: VO2@m-SiO2 nanoparticles are obtained.The vanadium dioxide-based thermochromic film prepared by VO2@m-SiO2 nanoparticles still maintains good thermochromic performance after 50 days in accelerated aging environment, showing super high durability.

Description

Technical Field

[0001] This invention relates to the field of energy-saving materials technology for VO2-based temperature-controlled smart windows, and in particular to a highly stable vanadium dioxide-based nanomaterial and its preparation and application. Background Technology

[0002] Vanadium dioxide (VO2) undergoes a reversible metal-insulator phase transition (MIT) at its critical temperature (68℃), exhibiting excellent thermochromic properties, making it an ideal material for fabricating thermochromic smart windows. To date, most research on VO2 smart windows has focused on increasing solar transmittance, lowering the phase transition temperature, improving solar energy regulation, and color modification. However, its environmental durability in practical applications remains a key factor restricting its development.

[0003] Current literature reports on methods to improve VO2 stability mainly involve coating the surface of VO2 with environmentally stable oxides to form a core-shell structure. SiO2, due to its excellent stability and transparency, is often chosen as a coating material. Gao Yanfeng et al. (Gao Y, Wang S, Luo H, et al. Energy & Environmental Science, 2012, 5(3): 6104-6110) and Wang Min et al. (Wang M, Tian J, Zhang H, et al. Rsc Advances, 2016, 6(110): 108286-108289) both used SiO2 to coat VO2 nanoparticles to improve its stability. However, these SiO2 shells prepared using alkaline catalysts are relatively porous. This porous structure allows environmental factors such as water and oxygen to penetrate the shell and react with the internal VO2, thus weakening the coating's effect on improving VO2 stability. Tong Kun et al. (Tong K, Li R, Zhu J, et al. Ceramics International, 43(2017) 4055-4061) attempted to coat the surface of VO2 nanoparticles with Al2O3 and obtain a dense Al-O-based shell through heat treatment. However, large thermal stress was generated between the core and shell during the heat treatment process, which led to shell cracking and reduced the protective effect of the coating layer on VO2. Chen Yunxiang et al. (Chen Y, Zeng X, Zhu J, et al. Acs Applied Materials & Interfaces, 2017, 9(33): 27784-27791) used ZnO with high refractive index to coat the surface of VO2 and obtained a dense protective layer after hydrothermal treatment, which significantly improved the stability of VO2. However, the powder agglomerated severely after treatment and needed to be dispersed in the later stage to meet the requirements of optical and appearance performance of window film products. However, the further dispersion process would damage the formed protective shell layer and lose the protective effect on the VO2 core. Therefore, we still need to conduct in-depth research and explore more effective coating strategies to further improve the stability of VO2 and meet the needs of practical applications.

[0004] Relevant literature indicates that TEOS can form a relatively dense SiO2 shell under acid catalysis. Wang Hui et al. (Wang H, Huang S, Zuo Y, et al. Corrosion Science, 2011, 53(1):161-167) used hydrochloric acid to catalyze the formation of a dense SiO2 shell on the surface of aluminum pigments using TEOS, which greatly improved the corrosion resistance of the aluminum pigments. However, VO2 is extremely sensitive to acidic environments, and prolonged exposure to acidic conditions can severely impair its thermochromic properties and even cause dissolution and denaturation. Therefore, in the existing coating process of VO2 nanoparticles, acid-catalyzed coating methods have not been adopted to avoid adverse effects on the performance of VO2.

[0005] Existing methods for coating VO2 have not considered the abrupt volume change that occurs before and after the VO2 phase transition. This volume change caused by the phase transition can easily generate stress in the coating shell, leading to cracking. Using SiO2 or other inorganic oxides alone as the coating shell is insufficient to solve this problem; therefore, the shell material structure needs to be designed to accommodate this unique physical property of the VO2 core. Summary of the Invention

[0006] To address the problem of cracking caused by stress in the coating shell due to the rapid volume change before and after the VO2 phase transition, this invention provides a highly stable vanadium dioxide-based nanomaterial, its preparation, and its application. This invention introduces siloxane monomers other than TEOS during VO2 coating to prepare a composite shell (m-SiO2). To obtain a dense coating shell, this invention employs an acid catalyst to prepare the highly stable vanadium dioxide-based nanomaterial; therefore, the VO2 nanoparticles are pretreated with L-ascorbic acid before coating to improve their acid resistance.

[0007] In the preparation process of the highly stable vanadium dioxide-based nanomaterials of this invention, TEOS and MTES are first dissolved together in an alcohol solvent to obtain mixture A; acidic catalyst, water and alcohol solvent are mixed evenly to obtain mixture B; L-ascorbic acid is dissolved in VO2 dispersion to pretreat VO2; mixture A and mixture B are added concurrently to the pretreated VO2 dispersion for coating treatment, thus obtaining highly stable VO2@m-SiO2 nanoparticles.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] The first objective of this invention is to provide a method for preparing highly stable vanadium dioxide-based nanomaterials, comprising the following steps:

[0010] (S1) Preparation of mixture A: The combination of TEOS and MTES is dissolved in a solvent to obtain mixture A;

[0011] (S2) Preparation of mixture B: The acidic catalyst, water and solvent are mixed evenly to obtain mixture B;

[0012] (S3) Ascorbic acid pretreatment: L-ascorbic acid was added to the VO2 dispersion to pretreat the VO2;

[0013] (S4) Preparation of VO2@m-SiO2 nanoparticles: The mixture A prepared in step (S1) and the mixture B prepared in step (S2) are added in parallel to the VO2 dispersion after pretreatment in step (S3) for coating treatment to obtain highly stable vanadium dioxide-based nanomaterials: VO2@m-SiO2 nanoparticles.

[0014] In one embodiment of the present invention, in step (S1), the solvent is selected from one or a combination of anhydrous ethanol, methanol, isopropanol, propylene glycol methyl ether acetate or acetone.

[0015] In one embodiment of the present invention, in step (S1), the molar ratio of TEOS, MTES and solvent is 1:0.1:24-1:2.5:38.

[0016] In one embodiment of the present invention, in step (S2), the acid solution is selected from one or a combination of sulfuric acid, nitric acid, hydrochloric acid or glacial acetic acid.

[0017] In one embodiment of the present invention, in step (S2), the solvent is selected from one or a combination of anhydrous ethanol, methanol, isopropanol, propylene glycol methyl ether acetate or acetone.

[0018] In one embodiment of the present invention, in step (S2), the mass ratio of acidic catalyst, water and solvent is 2-3:5:10.

[0019] In one embodiment of the present invention, in step (S3), the mass ratio of L-ascorbic acid to VO2 in the VO2 dispersion is 1:20-1:3.

[0020] In one embodiment of the present invention, the pretreatment time in step (S3) is 1-24 hours.

[0021] In one embodiment of the present invention, in step (S4), the mass ratio of mixture A, VO2 and mixture B is 4:1:3-3:1:2.

[0022] In one embodiment of the present invention, in step (S4), the coating treatment temperature is 20-70°C and the time is 10-24h.

[0023] In one embodiment of the present invention, in step (S4), the post-processing process involves washing with ethanol and deionized water in sequence, followed by drying.

[0024] The second objective of this invention is to provide a highly stable vanadium dioxide-based nanomaterial prepared by the above method.

[0025] The third objective of this invention is to provide an application of highly stable vanadium dioxide-based nanomaterials in the preparation of vanadium dioxide-based thermochromic thin films.

[0026] A mixture of highly stable vanadium dioxide-based nanomaterials was dispersed and mixed with a film-forming resin to obtain a mixture. The mixture was then uniformly coated onto a carrier and cured to obtain a vanadium dioxide-based thermochromic film.

[0027] In one embodiment of the present invention, the mass ratio of highly stable vanadium dioxide-based nanomaterials to film-forming resin is 1:25-35.

[0028] In one embodiment of the present invention, the film-forming resin has no special requirements, but a resin with high weather resistance and low water and oxygen permeability is preferred.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) In this invention, VO2 nanoparticles still maintain good thermochromic properties after being coated in an acidic environment; the protective shell of VO2@m-SiO2 nanoparticles prepared by acid catalysis is continuous, uniform and dense, and has high stability; the composite shell protection material is used, and the introduction of the second monomer increases the shell's adaptability to stress caused by the VO2 phase transition; the preparation process of VO2@m-SiO2 nanoparticles is simple, the raw materials required are relatively cheap, and the preparation process is safe and pollution-free.

[0031] (2) The vanadium dioxide-based thermochromic film prepared by the present invention using VO2@m-SiO2 nanoparticles still maintains good thermochromic properties after 50 days in an accelerated aging environment (temperature 60℃, humidity 100%), showing extremely high durability. Attached Figure Description

[0032] Figure 1 The image shows the XRD pattern of VO2@m-SiO2 nanoparticles in Example 2.

[0033] Figure 2 Acid resistance tests were conducted on untreated VO2 and the VO2@m-SiO2 nanoparticles prepared in Example 2; wherein, Figure 2 Figure a shows the acid resistance results after the sample was placed in 1M hydrochloric acid for 5 minutes. Figure 2b is a graph showing the acid resistance results after the sample was placed in 1M hydrochloric acid for 72 hours; label ① represents untreated VO2, and label ② represents VO2@m-SiO2 nanoparticles prepared in Example 2.

[0034] Figure 3 For the acid resistance test of VO2@m-SiO2 nanoparticles in Comparative Example 2; among them, Figure 3 Figure a shows the acid resistance results after the sample was placed in 1M hydrochloric acid for 5 minutes. Figure 2 b is the acid resistance result after the sample was placed in 1M hydrochloric acid for 4 hours; label ③ is the VO2@m-SiO2 nanoparticles prepared in Comparative Example 2.

[0035] Figure 4 The transmittance of the vanadium dioxide-based thermochromic film in Example 4 was tested after 50 days.

[0036] Figure 5 The transmittance of the vanadium dioxide-based thermochromic film in Comparative Example 3 was tested after 15 days.

[0037] Figure 6 The transmittance of the vanadium dioxide-based thermochromic film in Comparative Example 4 was tested after 30 days. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0039] Unless otherwise specified, all reagents used in the following embodiments are commercially available reagents, and all detection methods and techniques used are conventional detection methods and techniques in the art.

[0040] In the following examples and comparative examples, the raw materials used for preparation were vanadium dioxide (VO2), tetraethyl orthosilicate (TEOS), methyltriethoxysilane (MTES), sulfuric acid, ammonia, anhydrous ethanol, and L-ascorbic acid. All the selected raw materials were purchased from Sinopharm Chemical Reagent Co., Ltd., and were not further purified before use.

[0041] Example 1

[0042] This embodiment provides a highly stable vanadium dioxide-based nanomaterial and its preparation method.

[0043] (S1) Weigh 1.2g of VO2 nanoparticles and ultrasonically disperse them in 60g of anhydrous ethanol for 10min to obtain a well-dispersed VO2 dispersion. Keep the magnetic stirrer stirring continuously.

[0044] (S2) Weigh 0.5g of L-ascorbic acid and add it to the VO2 dispersion prepared in step (S1). React at 70℃ for 2h to obtain pretreated VO2.

[0045] Weigh 1.2g of TEOS and 2.4g of MTES (molar ratio of TEOS to MTES is 1:2.3) and add them to 10g of anhydrous ethanol. Let stand for 10min to mix thoroughly to obtain mixed solution A.

[0046] Weigh 2.6g of sulfuric acid and 5g of water and add them to 10g of anhydrous ethanol to obtain mixture B;

[0047] (S3) The mixture A and mixture B prepared in step (S2) are added in parallel to the pretreated VO2 dispersion for coating treatment. The reaction is stopped after 20 h. The reactants are washed three times with ethanol and deionized water and then dried in an oven at 60 °C to finally obtain highly stable VO2@m-SiO2 nanoparticles.

[0048] Example 2

[0049] This embodiment provides a highly stable vanadium dioxide-based nanomaterial and its preparation method.

[0050] (S1) Weigh 1.2g of VO2 nanoparticles and ultrasonically disperse them in 60g of anhydrous ethanol for 10min to obtain a well-dispersed VO2 dispersion. Keep the magnetic stirrer stirring continuously.

[0051] (S2) Weigh 0.5g of L-ascorbic acid and add it to the VO2 dispersion prepared in step (S1). React at 50℃ for 4h to obtain pretreated VO2.

[0052] Weigh 1.58g of TEOS and 2.02g of MTES (molar ratio of TEOS to MTES is 1:1.5) and add them to 10g of anhydrous ethanol. Let stand for 10 minutes to mix thoroughly to obtain mixture A.

[0053] Weigh 2.6g of sulfuric acid and 5g of water and add them to 10g of anhydrous ethanol to obtain mixture B;

[0054] (S3) Mixtures A and B prepared in step (S2) were added concurrently to the pretreated VO2 dispersion for coating treatment. The reaction was stopped after 20 h. The reactants were washed three times with ethanol and deionized water and then dried in an oven at 60 °C to finally obtain highly stable VO2@m-SiO2 nanoparticles (XRD pattern shown in figure). Figure 1 As shown, through Figure 1 It can be observed that all the peaks of VO2@m-SiO2 nanoparticles correspond to the peaks of VO2(M), indicating that the hybrid shell does not destroy the crystal structure of VO2 nanoparticles.

[0055] The VO2@m-SiO2 nanoparticles prepared in this embodiment were placed in 1M hydrochloric acid to test their acid resistance (e.g., Figure 2 As shown, untreated VO2 was used as the control group. Figure 2 It can be observed that the VO2@m-SiO2 nanoparticles prepared in this embodiment maintain high stability in an acidic environment and do not show any color change after 3 days.

[0056] Example 3

[0057] This embodiment provides a highly stable vanadium dioxide-based nanomaterial and its preparation method.

[0058] (S1) Weigh 1.2g of VO2 nanoparticles and ultrasonically disperse them in 60g of anhydrous ethanol for 10min to obtain a well-dispersed VO2 dispersion. Keep the magnetic stirrer stirring continuously.

[0059] (S2) Weigh 0.5g of L-ascorbic acid and add it to the VO2 dispersion prepared in step (S1). React at 20℃ for 6h to obtain pretreated VO2.

[0060] Weigh 1.94g of TEOS and 1.66g of MTES (the molar ratio of TEOS to MTES is 1:1) and add them to 10g of anhydrous ethanol. Let it stand for 10 minutes to mix thoroughly to obtain mixture A.

[0061] Weigh 2.6g of sulfuric acid and 5g of water and add them to 10g of anhydrous ethanol to obtain mixture B;

[0062] (S3) The mixture A and mixture B prepared in step (S2) are added in parallel to the pretreated VO2 dispersion for coating treatment. The reaction is stopped after 20 h. The reactants are washed three times with ethanol and deionized water and then dried in an oven at 60 ℃ to finally obtain highly stable VO2@m-SiO2 nanoparticles.

[0063] Comparative Example 1

[0064] This comparative example provides a vanadium dioxide-based nanomaterial and its preparation method (without ascorbic acid treatment).

[0065] (S1) Weigh 1.2g of VO2 nanoparticles and ultrasonically disperse them in 60g of anhydrous ethanol for 10min to obtain a well-dispersed VO2 dispersion. Keep the magnetic stirrer stirring continuously.

[0066] (S2) Weigh 1.2g of TEOS and 2.4g of MTES (the molar ratio of TEOS to MTES is 1:2.3) and add them to 10g of anhydrous ethanol. Let it stand for 10min to mix thoroughly to obtain mixture A.

[0067] Weigh 2.6g of sulfuric acid and 5g of water and add them to 10g of anhydrous ethanol to obtain mixture B;

[0068] (S3) Mixture A and mixture B prepared in step (S2) are added in parallel to the VO2 dispersion prepared in step (S1) for coating treatment. The reaction is stopped after 24 hours. The reactants are washed three times with ethanol and deionized water and then dried in an oven at 60°C to finally obtain VO2@m-SiO2 nanoparticles.

[0069] When the reaction product prepared in step (S3) of the comparative example was washed and centrifuged, the supernatant after centrifugation was observed to be transparent green. This phenomenon indicates that some of the VO2 nanoparticles had dissolved and denatured when coated in an acidic environment.

[0070] Comparative Example 2

[0071] This comparative example provides a vanadium dioxide-based nanomaterial and its preparation method under alkaline catalytic conditions (alkaline environment).

[0072] (S1) Weigh 1.2g of VO2 nanoparticles and ultrasonically disperse them in 60g of anhydrous ethanol for 10min to obtain a well-dispersed VO2 dispersion. Keep the magnetic stirrer stirring continuously.

[0073] (S2) Weigh 1.2g of TEOS and 2.4g of MTES (the molar ratio of TEOS to MTES is 1:2.3) and add them to 10g of anhydrous ethanol. Let it stand for 10min to mix thoroughly to obtain mixture A.

[0074] Weigh 2.6g of ammonia and 5g of water and add them to 10g of anhydrous ethanol to obtain mixture B;

[0075] (S3) Mixture A and mixture B prepared in step (S2) are added in parallel to the VO2 dispersion prepared in step (S1) for coating treatment. The reaction is stopped after 24 hours. The reactants are washed three times with ethanol and deionized water and then dried in an oven at 60°C to finally obtain VO2@m-SiO2 nanoparticles.

[0076] The VO2@m-SiO2 nanoparticles prepared in this comparative example were placed in 1M hydrochloric acid to test their acid resistance (e.g., Figure 3 As shown in the figure, it was found that the color of the VO2@m-SiO2 nanoparticles prepared in this comparative example changed significantly after 4 hours in 1M hydrochloric acid. Compared with Example 2, the stability of the VO2@m-SiO2 nanoparticles prepared in this comparative example was poor.

[0077] Example 4

[0078] This embodiment provides a vanadium dioxide-based thermochromic thin film and its preparation.

[0079] (S1) Weigh 0.1g of the VO2@m-SiO2 nanoparticles prepared in Example 2 and ultrasonically disperse them in 1g of anhydrous ethanol to obtain a well-dispersed VO2@m-SiO2 dispersion. Add 3g of vinyl silicone resin to the dispersion and stir continuously until homogeneous to obtain a resin mixture.

[0080] (S2) Take out a dry and clean glass slide, pour the resin mixture onto the glass slide and spread it evenly. After the film is placed at room temperature for 1 hour, it is transferred to an oven at 120°C to dry for 3 hours, and finally VO2@m-SiO2 thermochromic film is obtained.

[0081] The vanadium dioxide-based thermochromic film prepared in this embodiment was aged in an accelerated aging environment (temperature 60°C, humidity 100%). Figure 4 As shown in the figure, it was found that the VO2@m-SiO2 thermochromic film still maintained good thermochromic properties after 50 days, showing extremely high durability.

[0082] Comparative Example 3

[0083] This comparative example provides a vanadium dioxide-based thermochromic thin film and its preparation.

[0084] (S1) Weigh 0.1g of the VO2@m-SiO2 nanoparticles prepared in Comparative Example 1 and ultrasonically disperse them in 1g of anhydrous ethanol to obtain a well-dispersed VO2@m-SiO2 dispersion. Add 3g of methyl silicone resin to the dispersion and stir continuously until homogeneous to obtain a resin mixture.

[0085] (S2) Take out a dry and clean glass slide, pour the resin mixture onto the glass slide and spread it evenly. After the film is placed at room temperature for 1 hour, it is transferred to an oven at 120°C to dry for 3 hours, and finally VO2@m-SiO2 thermochromic film is obtained.

[0086] The vanadium dioxide-based thermochromic film prepared in this comparative example lost its thermochromic properties after 15 days in an accelerated aging environment (temperature 60℃, humidity 100%). Figure 5 As shown in the figure, an acidic catalytic environment will cause some VO2 to lose its phase change properties during the coating process.

[0087] Comparative Example 4

[0088] This comparative example provides a vanadium dioxide-based thermochromic thin film and its preparation.

[0089] (S1) Weigh 0.1g of the VO2@m-SiO2 nanoparticles prepared in Comparative Example 2 and ultrasonically disperse them in 1g of anhydrous ethanol to obtain a well-dispersed VO2@m-SiO2 dispersion. Add 3g of aqueous acrylic resin to the dispersion and stir continuously until homogeneous to obtain a resin mixture.

[0090] (S2) Take out a dry and clean glass slide, pour the resin mixture onto the glass slide and spread it evenly. After the film is placed at room temperature for 1 hour, it is transferred to an oven at 120°C to dry for 3 hours, and finally VO2@m-SiO2 thermochromic film is obtained.

[0091] The vanadium dioxide-based thermochromic film prepared in this comparative example retained some thermochromic properties after 30 days of accelerated aging (temperature 60℃, humidity 100%). Figure 6 (As shown), but at this time the solar energy regulation rate deteriorates, ΔT sol Only 1.69%. The reason is that the protective shell prepared by alkaline catalysis is continuous and uniform, but it is relatively loose and has poor density compared with the shell prepared by acid catalysis.

[0092] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the interpretation of the present invention, without departing from the scope of the invention, should be within the protection scope of the present invention.

Claims

1. A method for preparing a vanadium dioxide-based thermochromic thin film, characterized in that, A mixture of highly stable vanadium dioxide-based nanomaterials was dispersed and mixed with a film-forming resin to obtain a mixture. The mixture was then uniformly coated onto a carrier and cured to obtain a vanadium dioxide-based thermochromic film. The preparation method of highly stable vanadium dioxide-based nanomaterials includes the following steps: (S1) Dissolve the composition of TEOS and MTES in a first solvent to obtain mixture A; The first solvent is selected from one or a combination of anhydrous ethanol, methanol, or isopropanol. (S2) Mix the acidic catalyst, water and the second solvent to obtain mixture B; The second solvent is selected from one or a combination of anhydrous ethanol, methanol, or isopropanol; (S3) Add L-ascorbic acid to the VO2 dispersion to pretreat VO2; (S4) The mixture A prepared in step (S1) and the mixture B prepared in step (S2) are added concurrently to the VO2 dispersion prepared in step (S3) for coating treatment to obtain highly stable vanadium dioxide-based nanomaterials: VO2@m-SiO2 nanoparticles. In step (S1), the molar ratio of TEOS, MTES, and the first solvent is 1:0.1:24-1:2.5:38; In step (S2), the acidic catalyst is selected from one or a combination of sulfuric acid, nitric acid, hydrochloric acid or glacial acetic acid; the mass ratio of the acidic catalyst, water and the second solvent is 2-3:5:

10. In step (S3), the mass ratio of L-ascorbic acid to VO2 in the VO2 dispersion is 1:20-1:3; the pretreatment time is 1-24 h. In step (S4), the mass ratio of mixture A, VO2 and mixture B is 4:1:3-3:1:2; the coating treatment temperature is 20-70℃ and the time is 10-24 h. Among them, the vanadium dioxide-based thermochromic film prepared based on highly stable vanadium dioxide-based nanomaterials still maintains good thermochromic properties after 50 days in an environment with a temperature of 60℃ and a humidity of 100%. The mass ratio of highly stable vanadium dioxide-based nanomaterials to film-forming resin is 1:25-35.

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