Method for preparing high-crystallinity monodisperse m-phase vanadium dioxide nanopowder

Abstract

The application discloses a preparation method of high-crystallinity monodisperse M-phase vanadium dioxide nano powder, which comprises the following steps: dissolving a tetravalent vanadium compound in benzyl alcohol, and obtaining D-phase vanadium dioxide nano powder through a solvothermal reaction and a purification treatment; and annealing the D-phase vanadium dioxide powder to obtain the high-crystallinity monodisperse M-phase vanadium dioxide nano powder, wherein the annealing temperature is 250-600 DEG C, the annealing time is 30-480 min, and the oxygen concentration is 1-20 vol.%. The obtained powder has the characteristics of high crystallinity, high purity, good dispersity and small particle size, the phase transition enthalpy of the obtained M-phase vanadium dioxide nano powder reaches 45-50 J / g, the average particle size reaches 30-40 nm, the cost is low, the process is simple, the yield is close to 100%, and the powder is easy to be produced in an industrial scale.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a method for preparing vanadium dioxide nanopowder. Background Technology

[0002] Vanadium dioxide (VO2(M / R)) undergoes a reversible phase transition from a high-temperature tetragonal metallic phase (R phase) to a low-temperature monoclinic semiconductor phase (M phase) around 68℃. Accompanying this phase transition, its electrical and optical properties undergo abrupt changes. This characteristic makes M-phase vanadium dioxide a promising candidate for applications in smart energy-saving thin films, radiative cooling devices, thermistor switches, infrared detectors, and optoelectronic switching materials. However, the difficulty in preparing vanadium dioxide materials severely hinders its commercialization. As is well known, vanadium exists in multiple valence states, including +2, +3, +4, and +5. During preparation, the redox environment must be strictly controlled to prevent vanadium from changing its valence. Furthermore, even the +4 valence vanadium ion has numerous allotropes, including known structures such as A, B, C, D, M, R, and T. The formation energies between these allotropes are small, but only the M-phase vanadium dioxide possesses excellent thermochromic properties. Therefore, the preparation of the M-phase requires strict control of thermodynamic conditions. Preparing the M-phase from the perspective of chemical composition and crystal structure alone is extremely difficult, let alone considering the control of its microstructure during the preparation process. Nanoscale M-phase vanadium dioxide often possesses unique properties not found in bulk vanadium dioxide. Furthermore, various bulk or thin-film M-phase vanadium dioxide devices can be easily synthesized using M-phase vanadium dioxide nanoparticles as the basic unit. Therefore, the large-scale preparation of nanoscale M-phase vanadium dioxide is crucial for the development and application of vanadium dioxide.

[0003] Currently, the main method for preparing vanadium dioxide nanoparticles is the hydrothermal method. Chinese invention patents CN101391814A, CN 104071843A, CN 104045345A, and CN103936071A all disclose methods for preparing rutile-phase vanadium dioxide powder based on the hydrothermal method. Although the particle size can be controlled to as low as approximately 20 nm, vanadium dioxide generally exhibits low crystallinity, resulting in a low phase transition enthalpy (less than 40 J / g). These reported vanadium dioxide nanoparticles cannot simultaneously possess both high crystallinity and small nanoscale characteristics. Smaller nanoparticles are typically prepared at lower reaction temperatures, but these particles contain numerous lattice defects, resulting in poor crystallinity. Alternatively, increasing the reaction temperature can improve the crystallinity, but the small particles tend to aggregate and grow into larger particles. Importantly, the degree of crystallinity directly affects its thermochromic properties; higher crystallinity results in better thermochromic performance. Furthermore, hydrothermal reactions have the following significant drawbacks: they require prolonged reaction at high temperatures (above 240°C) (greater than 24 hours), and the high pressure generated by the high-temperature hydrothermal reaction increases the risk of the reaction; they require strict control of the pH, redox environment, reactant concentration, and packing density of the reaction system, resulting in complex raw materials and processes; overall, the most advanced methods for preparing VO2 nanoparticles currently available are complex, costly, and have low yields. Most importantly, existing technologies cannot prepare vanadium dioxide nanoparticles that simultaneously possess high crystallinity (phase transition enthalpy exceeding 40 J / g), monodisperse state, and particle size less than 50 nm. Currently, commercially available VO2 nanoparticles cost over 200 yuan per gram, and exhibit particle agglomeration and poor crystallinity. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing monodisperse M-phase vanadium dioxide nanopowder with high crystallinity. The resulting powder has the characteristics of high crystallinity, high purity, good dispersibility and small particle size. The phase transition enthalpy of the obtained M-phase vanadium dioxide nanopowder reaches 45-50 J / g and the average particle size reaches 30-40 nm. At the same time, it is low in cost, simple in process, has a yield close to 100% and is easy to produce on an industrial scale.

[0005] To achieve the above objectives, the following technical solution is adopted:

[0006] A method for preparing highly crystalline monodisperse M-phase vanadium dioxide nanopowder includes the following steps:

[0007] (1) Dissolve tetravalent vanadium compounds in benzyl alcohol, and after solvothermal reaction, vanadium dioxide nanopowder of D phase is obtained by purification.

[0008] (2) Anneal the above D-phase vanadium dioxide powder to obtain monodisperse M-phase vanadium dioxide nanopowder with high crystallinity.

[0009] According to the above scheme, the tetravalent vanadium compound in step (1) is a soluble tetravalent vanadium salt.

[0010] According to the above scheme, the tetravalent vanadium compound in step (1) is one or any mixture of vanadium oxysulfate, vanadium acetylacetonate, vanadium dichloride, and vanadium oxalate.

[0011] According to the above scheme, the solvothermal reaction temperature in step (1) is not lower than 140°C and the reaction time is not lower than 4h.

[0012] According to the above scheme, step (1) further includes adding a surfactant in the solvothermal reaction; the surfactant is one or any combination of polyethylene glycol, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate; the concentration of the surfactant is from 0.001 mol / L to 0.1 mol / L.

[0013] According to the above scheme, the annealing temperature in step (2) is 250-600℃, the time is 30-480 min, and the oxygen concentration is 1-20 VT.

[0014] In the optimized scheme, the annealing temperature in step (2) is 350-450℃, the time is 30-120min, and the oxygen concentration is 3-10vt%.

[0015] According to the above scheme, in the annealing process of step (2), the crystallinity and particle size of the M-phase vanadium dioxide nanopowder are controlled by adjusting the annealing temperature and oxygen concentration; the higher the annealing temperature, the higher the crystallinity of the M-phase vanadium dioxide nanopowder and the larger the particle size; the higher the oxygen concentration, the higher the crystallinity of the M-phase vanadium dioxide nanopowder and the larger the particle size.

[0016] A method for preparing modified D-phase vanadium dioxide nanopowder includes the following steps:

[0017] Soluble tetravalent vanadium compounds were dissolved in benzyl alcohol, and elemental dopants were added. The mixture was reacted at a temperature of not less than 140°C for not less than 4 hours, and then purified to obtain modified D-phase vanadium dioxide nanopowder.

[0018] A method for preparing modified M-phase vanadium dioxide nanopowder includes the following steps:

[0019] (1) Dissolve a soluble tetravalent vanadium compound in benzyl alcohol, add an elemental dopant, react at a temperature of not less than 140°C for not less than 4 hours, and then purify to obtain modified D-phase vanadium dioxide nanopowder.

[0020] (2) The modified D-phase vanadium dioxide nanopowder was annealed at 250-600℃ for 30-480 min at an oxygen concentration of 1-20vt% to obtain the modified M-phase vanadium dioxide nanopowder.

[0021] According to the above scheme, the dopant is one or any combination of soluble salts of boron, nitrogen, magnesium, aluminum, silicon, titanium, chromium, iron, cobalt, nickel, gallium, zirconium, niobium, molybdenum, tin, antimony, hafnium, tantalum, and tungsten; the molar ratio of the dopant element to vanadium element is (0.001-0.2):1.

[0022] When tetravalent vanadium compounds dissolve in benzyl alcohol, vanadium oxide ions combine with the hydroxyl groups in benzyl alcohol to form vanadium hydroxide. These vanadium hydroxides then undergo dehydration condensation to form D-phase vanadium dioxide nanoparticles. Adding surfactants to the reactants helps improve the crystallinity and morphology of the D-phase vanadium dioxide nanoparticles. Surfactants can adhere to the surface of the formed crystals, binding reactant ions in the solution and allowing them to directionally attach to the crystal surface. This reduces the energy required for crystal growth and improves the crystallinity of the D-phase vanadium dioxide nanoparticles. Furthermore, surfactant ions can also directionally attach to certain specific crystal faces of the D-phase vanadium dioxide nanocrystals, allowing for preferential growth on these faces and thus controlling the morphology of the D-phase vanadium dioxide nanocrystals.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention utilizes a solvothermal method followed by low-temperature heat treatment to prepare monodisperse M-phase vanadium dioxide nanopowder with high crystallinity. The M-phase vanadium dioxide nanopowder exhibits good crystallinity, with a phase transition enthalpy reaching a maximum of 47 J / g, approaching that of bulk vanadium dioxide. Furthermore, its average particle size is less than 50 nm, demonstrating good dispersibility.

[0025] The method for preparing M-phase vanadium dioxide nanoparticles proposed in this invention represents a significant improvement over the most advanced existing hydrothermal methods. Key improvements include: readily available and simple reactants requiring only two reactants, resulting in lower preparation costs; milder reaction conditions compared to hydrothermal methods, simplifying operation and enhancing safety; and a high yield, approaching 100%. In summary, this method is highly suitable for large-scale industrial production. Most importantly, it overcomes the limitation of hydrothermal methods in preparing vanadium dioxide nanoparticles that simultaneously possess high crystallinity and small size. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below.

[0027] Figure 1 XRD pattern of M-phase vanadium dioxide nanopowder prepared in Example 1.

[0028] Figure 2 TEM image of the M-phase vanadium dioxide nanopowder prepared in Example 1.

[0029] Figure 3DSC image of the M-phase vanadium dioxide nanopowder prepared in Example 1. Detailed Implementation

[0030] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0031] A specific embodiment provides a method for preparing highly crystalline monodisperse M-phase vanadium dioxide nanopowder:

[0032] (1) Dissolve tetravalent vanadium compounds in benzyl alcohol, and after solvothermal reaction, vanadium dioxide nanopowder of D phase is obtained by purification.

[0033] (2) Anneal the above D-phase vanadium dioxide powder to obtain monodisperse M-phase vanadium dioxide nanopowder with high crystallinity.

[0034] Specifically, the tetravalent vanadium compound in step (1) is a soluble tetravalent vanadium salt. The tetravalent vanadium compound is one or any mixture of vanadium oxysulfate, vanadium acetylacetonate, vanadium dichloride, and vanadium oxalate.

[0035] Specifically, the solvothermal reaction temperature in step (1) is not lower than 140°C and the reaction time is not lower than 4 hours.

[0036] Specifically, step (1) further includes adding a surfactant in the solvothermal reaction; the surfactant is one or any combination of polyethylene glycol, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate; the concentration of the surfactant is from 0.001 mol / L to 0.1 mol / L.

[0037] Specifically, in step (2), the annealing temperature is 250–600°C, the time is 30–480 min, and the oxygen concentration is 1–20 wt%.

[0038] In the optimized scheme, the annealing temperature in step (2) is 350-450℃, the time is 30-120min, and the oxygen concentration is 3-10vt%.

[0039] Specifically, in step (2) annealing, the crystallinity and particle size of the M-phase vanadium dioxide nanopowder are controlled by adjusting the annealing temperature and oxygen concentration; the higher the annealing temperature, the higher the crystallinity of the M-phase vanadium dioxide nanopowder and the larger the particle size; the higher the oxygen concentration, the higher the crystallinity of the M-phase vanadium dioxide nanopowder and the larger the particle size.

[0040] A specific embodiment also provides a method for preparing modified D-phase vanadium dioxide nanopowder, including the following steps:

[0041] Soluble tetravalent vanadium compounds were dissolved in benzyl alcohol, and elemental dopants were added. The mixture was reacted at a temperature of not less than 140°C for not less than 4 hours, and then purified to obtain modified D-phase vanadium dioxide nanopowder.

[0042] A specific embodiment also provides a method for preparing modified M-phase vanadium dioxide nanopowder, including the following steps:

[0043] (1) Dissolve a soluble tetravalent vanadium compound in benzyl alcohol, add an elemental dopant, react at a temperature of not less than 140°C for not less than 4 hours, and then purify to obtain modified D-phase vanadium dioxide nanopowder.

[0044] (2) The modified D-phase vanadium dioxide nanopowder was annealed at 250-600℃ for 30-480 min at an oxygen concentration of 1-20vt% to obtain the modified M-phase vanadium dioxide nanopowder.

[0045] Specifically, the dopant is one or any combination of soluble salts of boron, nitrogen, magnesium, aluminum, silicon, titanium, chromium, iron, cobalt, nickel, gallium, zirconium, niobium, molybdenum, tin, antimony, hafnium, tantalum, and tungsten; the molar ratio of the dopant element to vanadium is (0.001-0.2):1.

[0046] Example 1

[0047] A method for preparing highly crystalline monodisperse M-phase vanadium dioxide nanopowder:

[0048] 1) Vanadium oxysulfate was dissolved in benzyl alcohol, and the solution was reacted at 180°C for 24 hours. The mixture after reaction was separated by centrifugation, thoroughly washed and dried to obtain the D-phase vanadium dioxide precursor.

[0049] 2) The above-mentioned D-phase vanadium dioxide precursor was placed in a tube furnace for heat treatment at a temperature of 400℃ for 60 min with an oxygen concentration of 6% to obtain monodisperse M-phase vanadium dioxide nanopowder with high crystallinity.

[0050] Example 2

[0051] A method for preparing highly crystalline monodisperse M-phase vanadium dioxide nanopowder:

[0052] 1) Vanadium acetylacetonate was dissolved in benzyl alcohol, and the solution was reacted at 220℃ for 8 hours. The mixture after reaction was separated by centrifugation, thoroughly washed and dried to obtain the D-phase vanadium dioxide precursor.

[0053] 2) The above-mentioned D-phase vanadium dioxide powder was placed in a tube furnace for heat treatment at a temperature of 350°C for 120 min with an oxygen concentration of 5% to obtain monodisperse M-phase vanadium dioxide nanopowder with high crystallinity.

[0054] Example 3

[0055] A method for preparing highly crystalline monodisperse M-phase vanadium dioxide nanopowder:

[0056] 1) Vanadium oxychloride was dissolved in benzyl alcohol, and the solution was reacted at 200℃ for 12h. The mixture after reaction was separated by centrifugation, thoroughly washed and dried to obtain the D-phase vanadium dioxide precursor.

[0057] 2) The above-mentioned D-phase vanadium dioxide precursor was placed in a tube furnace for heat treatment at a temperature of 450°C for 45 min and an oxygen concentration of 6.5% to obtain monodisperse M-phase vanadium dioxide nanopowder with high crystallinity.

[0058] Example 4

[0059] A method for preparing highly crystalline monodisperse M-phase vanadium dioxide nanopowder:

[0060] 1) Vanadium oxysulfate and hexadecyltrimethylammonium bromide were dissolved in benzyl alcohol. The amount of hexadecyltrimethylammonium bromide added was 0.001 mol. The solution was reacted at 180℃ for 24 h. The mixture after reaction was separated by centrifugation, thoroughly washed and dried to obtain the D-phase vanadium dioxide precursor.

[0061] 2) The above-mentioned D-phase vanadium dioxide precursor was placed in a tube furnace for heat treatment at a temperature of 300℃ for 120 min with an oxygen concentration of 6% to obtain monodisperse M-phase vanadium dioxide nanopowder with high crystallinity.

[0062] Example 5

[0063] A method for preparing modified M-phase vanadium dioxide nanopowder:

[0064] 1) Vanadium dichloride and ammonium tungstate were dissolved in benzyl alcohol, with a tungsten to vanadium ratio of 0.02:1. The solution was reacted at 200℃ for 12 hours. The mixture after reaction was centrifuged, thoroughly washed, and dried to obtain a tungsten-doped D-phase vanadium dioxide precursor.

[0065] 2) The above tungsten-doped D-phase vanadium dioxide precursor was placed in a tube furnace for heat treatment at a temperature of 450°C for 45 min and an oxygen concentration of 6.5% to obtain monodisperse tungsten-doped M-phase vanadium dioxide nanopowder with high crystallinity.

[0066] Performance tests were performed on the powders obtained in the examples.

[0067] 1. X-ray diffraction analysis

[0068] The Empyrean X-ray diffraction analyzer from Panaco in the Netherlands uses a copper target (Cu-Kα) as the radiation source (λ = 0.154178 nm), has a rated output power of 4 kW, a scanning range of 10-80°, and a scanning speed of 5° per minute.

[0069] 2. Field emission transmission electron microscopy

[0070] The morphology of M-phase vanadium dioxide nanoparticles was observed using a JEOL JEM-2100F field emission high-resolution transmission electron microscope.

[0071] 3. Differential scanning calorimetry

[0072] The phase transition temperature of M-phase vanadium dioxide powder was measured using a TA-DSC2500 differential scanning calorimeter from Thermo Fisher Scientific (TAS) under a nitrogen atmosphere.

[0073] Figure 1 The image shows the XRD pattern of the M-phase vanadium dioxide nanopowder obtained in Example 1. It can be seen from the figure that its diffraction peaks correspond to the standard M-phase vanadium dioxide card. Its diffraction peak intensity is high, indicating good crystallinity.

[0074] Figure 2 The image shows a TEM image of the M-phase vanadium dioxide nanopowder obtained in Example 1. It can be seen that the powder is generally spherical with no specific morphology, and the particle size is less than 100 nm, with an average particle size of less than 50 nm. Furthermore, the particles are monodisperse without agglomeration.

[0075] Figure 3 The image shows the DSC diagram of the M-phase vanadium dioxide nanopowder obtained in Example 1. The phase transition temperature of the powder is 67.1℃, corresponding to a phase transition enthalpy of 47 J / g, while the reported phase transition enthalpy of bulk vanadium dioxide is 51 J / g. It is generally believed that the closer the phase transition enthalpy is to this value, the better the crystallinity and the higher the purity of vanadium dioxide. Therefore, this also proves that the M-phase vanadium dioxide nanopowder prepared by this invention has very high crystallinity and purity.

[0076] The particle size, phase transition temperature and phase transition enthalpy of the vanadium dioxide nanopowder obtained in Examples 1-5 were characterized, and the characterization data are shown in Table 1.

[0077] Table 1

[0078] Example 1 Example 2 Example 3 Example 4 Example 5 Average particle size 43.6nm 34.5nm 57.3nm 20.9nm 42.1nm Phase transition temperature 67.1℃ 58.6℃ 68.3℃ 55.0℃ 20.1℃ Phase transition enthalpy 47.0 J / g 26.7 J / g 48.1 J / g 18.4 J / g 23.5J / g

[0079] All the raw materials listed in this invention, as well as the upper and lower limits and ranges of the raw materials and the upper and lower limits and ranges of the process parameters (such as temperature, time, etc.), can realize this invention. Examples are not listed one by one here.

[0080] The above description is merely a preferred embodiment of the present invention, and should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing highly crystalline monodisperse M-phase vanadium dioxide nanopowder, characterized in that... Includes the following steps: (1) A tetravalent vanadium compound is dissolved in benzyl alcohol, and after solvothermal reaction, it is purified to obtain D-phase vanadium dioxide nanopowder; the solvothermal reaction temperature is not lower than 140℃ and the reaction time is not lower than 4h; a surfactant is added to the solvothermal reaction, and the surfactant is one or any combination of polyethylene glycol, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate; the concentration of the surfactant is 0.001 mol / L to 0.1 mol / L; (2) The above D-phase vanadium dioxide nanopowder is annealed to obtain monodisperse M-phase vanadium dioxide nanopowder with high crystallinity; wherein the annealing temperature is 250~600℃, the time is 30~480min, and the oxygen concentration is 1-20vt.

2. The method for preparing highly crystalline monodisperse M-phase vanadium dioxide nanopowder as described in claim 1, characterized in that... The tetravalent vanadium compound mentioned in step (1) is a soluble tetravalent vanadium salt.

3. The method for preparing highly crystalline monodisperse M-phase vanadium dioxide nanopowder as described in claim 1, characterized in that... The tetravalent vanadium compound in step (1) is one or any mixture of vanadium oxysulfate, vanadium acetylacetonate, vanadium dichloride, and vanadium oxalate.

4. The method for preparing highly crystalline monodisperse M-phase vanadium dioxide nanopowder as described in claim 1, characterized in that... In step (2), the annealing temperature is 350-450 ℃, the time is 30~120 min, and the oxygen concentration is 3-10vt.

5. The method for preparing highly crystalline monodisperse M-phase vanadium dioxide nanopowder as described in claim 1, characterized in that... In step (2) annealing, the crystallinity and particle size of the M-phase vanadium dioxide nanopowder are controlled by adjusting the annealing temperature and oxygen concentration; the higher the annealing temperature, the higher the crystallinity of the M-phase vanadium dioxide nanopowder and the larger the particle size. The higher the oxygen concentration, the higher the crystallinity of the M-phase vanadium dioxide nanoparticles, and the larger the particle size.

6. A method for preparing modified D-phase vanadium dioxide nanopowder, characterized in that... Includes the following steps: A soluble tetravalent vanadium compound was dissolved in benzyl alcohol, and an elemental dopant was added. The mixture was reacted at a temperature not lower than 140°C for not less than 4 hours, and then purified to obtain modified D-phase vanadium dioxide nanopowder. A surfactant was added to the reaction, wherein the surfactant was one or any combination of polyethylene glycol, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, sodium dodecyl sulfonate, and sodium dodecylbenzene sulfonate; and the concentration of the surfactant was from 0.001 mol / L to 0.1 mol / L.

7. A method for preparing modified M-phase vanadium dioxide nanopowder, characterized in that... Includes the following steps: (1) Dissolve a soluble tetravalent vanadium compound in benzyl alcohol, add an elemental dopant, and react at a temperature not lower than 140°C for not less than 4 hours. Then, purify the mixture to obtain modified D-phase vanadium dioxide nanopowder. Add a surfactant to the reaction. The surfactant is one or any combination of polyethylene glycol, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, sodium dodecyl sulfonate, and sodium dodecylbenzene sulfonate. The concentration of the surfactant is 0.001 mol / L to 0.1 mol / L. (2) The modified D-phase vanadium dioxide nanopowder was annealed at 250~600℃ for 30~480min at an oxygen concentration of 1-20vt% to obtain the modified M-phase vanadium dioxide nanopowder.

Images