Preparation method of nano vanadium dioxide

Abstract

The invention provides a preparation method of nano vanadium dioxide. According to the preparation method, a sol-gel method and a micro-scale confinement space reaction are combined, the sol-gel method can realize uniform mixing of raw materials in a liquid phase, a stable sol system is formed through hydrolysis and condensation chemical reactions, and the micro-scale confinement space reaction limits nucleation and growth processes through a micro-nano-scale physical space, so that the micro-scale confinement space reaction is formed. According to the preparation method, the material is subjected to'guiding 'growth, vanadium ion form transformation and ultrafine particle nucleation growth can be realized in one step, preparation of nano powder with given structural characteristics is realized, meanwhile, the phenomenon of product agglomeration is avoided, and the powder prepared by the process method is relatively high in particle size controllability and good in dispersity.

Description

Technical Field

[0001] The invention belongs to the technical field of vanadium dioxide preparation, and specifically relates to a method for preparing nano vanadium dioxide. Background Art

[0002] At present, the main preparation methods of VO2 powder include thermal decomposition, chemical precipitation, sol-gel, laser-induced vapor deposition, hydrothermal synthesis, etc., but all of them have some shortcomings. Among them, the thermal decomposition method has a fierce redox reaction, and it is inevitable that vanadium oxides of other valence states will exist in the prepared powder. The hydrothermal method and microwave hydrothermal method have simple processes, and the prepared powder has high purity, controllable shape and size, and low degree of agglomeration, but the process control is difficult and it is difficult to achieve industrialization. The sol-gel method has a simple process, high powder purity, good experimental repeatability, but a long reaction cycle and high energy consumption. Although the chemical precipitation method has a simple preparation process, the prepared powder has a large and uneven particle size. In addition, the above preparation methods are mostly prepared using high-purity vanadium raw materials, which greatly increases the preparation cost.

[0003] CN104071843A discloses a method for preparing monodisperse M-phase vanadium dioxide nanoparticles. The method comprises mixing vanadium pentoxide, dihydrated oxalic acid and water in proportion, adding a surfactant and stirring to obtain a precursor solution, preparing the solution by hydrothermal reaction, performing solid-liquid separation and washing to obtain vanadium dioxide powder, and subjecting the powder to nitrogen heat treatment to obtain M-phase vanadium dioxide nanoparticles. The powder prepared by the invention has a small particle size and good dispersibility, but has a high cost, a long process flow and is not easy to realize industrial production.

[0004] CN109319838A discloses a method for preparing rutile phase vanadium dioxide ultrafine nano powder. The method adopts ammonia water and an acidic tetravalent vanadium solution to react to obtain a suspension, and the suspension is sealed, heat-insulated and stirred to obtain a colloidal suspension, and solid-liquid separation and cleaning are performed to obtain a hydrated hydroxide vanadium oxycolloid, which is then dried and sintered in a protective atmosphere to obtain rutile phase vanadium dioxide ultrafine nano powder. The rutile phase vanadium dioxide particles prepared by the process method of the invention have high purity, small size and uniformity, but the process is too complicated and the cost is high, separation is difficult, and it is not easy to achieve large-scale production.

[0005] Therefore, in view of the problems of large particle size, uneven distribution, complex preparation process, high production cost and low preparation efficiency in the current vanadium dioxide preparation methods, developing an efficient and low-cost synthesis technology for nano vanadium dioxide is an urgent problem to be solved in the application of VO2 in the field of functional materials. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a method for preparing nano vanadium dioxide. The method has low cost, high reaction efficiency, and small particle size and uniform distribution of nano vanadium dioxide.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for preparing nano vanadium dioxide, comprising the following steps:

[0009] S1: Mixing the vanadium source with the precipitant and the composite dispersant in an acidic environment, and reacting in a microscale confined space to obtain a vanadium dioxide precursor;

[0010] The composite dispersant comprises citric acid and an acid catalyst, wherein the acid catalyst is selected from any one or more of nitric acid, acetic acid or hydrochloric acid;

[0011] S2: heat-treating the vanadium dioxide precursor in an inert atmosphere to obtain nano-vanadium dioxide.

[0012] Preferably, the molar ratio of the citric acid to the acid catalyst is (2-4):1.

[0013] Preferably, the vanadium source is a vanadium-containing leaching solution.

[0014] Preferably, the precipitant is selected from any one or more of ammonium carbonate, sodium carbonate, sodium hydroxide or sodium bicarbonate.

[0015] Preferably, the precipitant and the composite dispersant are mixed with the vanadium source in the form of a precipitant solution and a composite dispersant solution, respectively.

[0016] Preferably, the molar ratio of the concentration of the precipitant solution to the vanadium concentration in the vanadium source is 1:(2-10).

[0017] Preferably, the molar ratio of the concentration of the composite dispersant solution to the vanadium concentration in the vanadium source is 1:(1.5-5).

[0018] Preferably, the volume ratio of the precipitant solution, the composite dispersant solution and the vanadium source is (4-1):(2-0.5):1.

[0019] Preferably, the pH of the acidic environment is 1-5.

[0020] Preferably, the reaction temperature is 40-100° C. and the reaction time is 10-120 min.

[0021] Preferably, the reaction is carried out in a rotating liquid film reactor.

[0022] Preferably, after the reaction is completed, washing, filtering and drying steps are also included.

[0023] Preferably, the heat treatment is performed at a temperature of 300-700° C. and for a time of 1-4 h.

[0024] Preferably, the heat treatment further includes a grinding step.

[0025] Preferably, the average particle size of the nano vanadium dioxide is 50-100 nm.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention provides a method for preparing nano vanadium dioxide by combining a sol-gel method with a microscale confined space reaction. The preparation method adopts a confined synthesis technology to prepare a vanadium dioxide precursor, and utilizes the liquid film space of a microscale reaction to make the nucleation process of the vanadium dioxide precursor proceed in a microscopic uniform environment. The nucleation process is controllable. The synthesis method starts from the crystal rapid nucleation-limited growth theory, and has advantages that the current conventional processes do not have. The obtained particles have a smaller particle size and a narrower particle size distribution, and are easy to realize industrial production.

[0028] In addition, in the process of synthesizing the vanadium dioxide precursor of the present invention, the citric acid in the composite dispersant plays a dispersing role on the one hand, forming a sol-gel so that the precursor particles are evenly dispersed, and on the other hand plays a reducing role, reducing the high-valent vanadium ions in the vanadium source to tetravalent vanadium ions. At the same time, the acid catalyst in the composite dispersant is conducive to the above-mentioned reduction.

[0029] In summary, the present invention adopts the sol-gel method and micro-scale confined space reaction, which can achieve uniform mixing of raw materials in the liquid phase, form a stable sol system in the micro-scale space, and effectively control the particle size and uniformity of the synthesized nano-vanadium dioxide powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a SEM image of the vanadium dioxide nanopowder prepared in Example 1;

[0031] Figure 2 This is the SEM image of the vanadium dioxide nanopowder prepared in Comparative Example 2. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The present invention provides a method for preparing nano vanadium dioxide, comprising the following steps:

[0034] S1: Mixing the vanadium source with the precipitant and the composite dispersant in an acidic environment, and reacting in a microscale confined space to obtain a vanadium dioxide precursor;

[0035] The composite dispersant comprises citric acid and an acid catalyst, wherein the acid catalyst is selected from any one or more of nitric acid, acetic acid or hydrochloric acid;

[0036] S2: heat-treating the vanadium dioxide precursor in an inert atmosphere to obtain nano-vanadium dioxide.

[0037] According to the present invention, the vanadium source is first mixed with a precipitant and a composite dispersant in an acidic environment. In the present invention, the pH of the acidic environment is 1 to 5, preferably 1 to 3. The present invention preferably mixes the vanadium source with the precipitant and the composite dispersant in an acidic environment, which is conducive to the subsequent nucleation and growth of the vanadium dioxide precursor.

[0038] In the present invention, the vanadium source may be a vanadium-containing leaching solution or other vanadium-containing substances commonly used in the art, such as a pentavalent vanadium solution. The vanadium source is preferably present in the form of a solution.

[0039] The present invention preferably uses vanadium-containing leaching solution as raw material from the perspective of cost, and does not need to be prepared by high-purity vanadium raw materials, which can greatly reduce the preparation cost. The vanadium-containing leaching solution is generally a vanadium-containing solution obtained by leaching vanadium ore after salt addition roasting and water leaching, in which the vanadium ions are mainly tetravalent vanadium and pentavalent vanadium.

[0040] In the present invention, the precipitant is alkaline and can undergo an acid-base reaction in an acidic environment, thereby causing a slow change in pH. In this process, vanadium ions will gradually change with the change in system pH. After being converted into vanadium oxide intermediates, they will rapidly nucleate to form precursor particles.

[0041] In some embodiments of the present invention, the precipitant is selected from any one or more of ammonium carbonate, sodium carbonate, sodium hydroxide or sodium bicarbonate; the precipitant is preferably mixed with the vanadium source in the form of a precipitant solution, and the molar ratio of the concentration of the precipitant solution to the vanadium concentration in the vanadium source solution is preferably 1:(2-10), such as 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, etc.

[0042] In the present invention, the composite dispersant comprises citric acid and an acid catalyst, wherein the acid catalyst is an acidic substance having a higher acidity than citric acid, and is specifically selected from any one or more of nitric acid, acetic acid or hydrochloric acid. The molar ratio of the citric acid to the acid catalyst is (2-4):1, preferably (2.5-3.5):1.

[0043] The above-mentioned precipitant and the proportion range of the dispersant have an impact on the existence form of the vanadium ions. Therefore, in some embodiments of the present invention, the above-mentioned proportion is preferably adopted. Among them, citric acid plays a dispersing role on the one hand, so that the sol-gel is formed during the reaction to ensure the uniform dispersion of the precursor particle formation process, and on the other hand, it plays a reducing role, reducing the high-valent vanadium ions in the vanadium source to tetravalent vanadium ions. The presence of an acid catalyst can further facilitate the process of reducing the above-mentioned high-valent vanadium ions to tetravalent vanadium ions. Therefore, the present invention preferably uses the above-mentioned composite dispersant mixed with the vanadium source.

[0044] In some embodiments of the present invention, the composite dispersant is preferably mixed with the vanadium source in the form of a composite dispersant solution. The molar ratio of the concentration of the composite dispersant solution to the vanadium concentration in the vanadium source solution is 1:(1.5-5), such as 1:1.5, 1:2, 1:3, 1:4 or 1:5, etc., to ensure that the particle size of the powder is within an appropriate range.

[0045] In some embodiments of the present invention, according to the concentration of the above-mentioned precipitant solution and the concentration of the composite dispersant solution, the volume ratio of the precipitant solution, the composite dispersant solution and the vanadium source is preferably (1~4):(0.5~2):1, and more preferably (1.5~3):(1~1.5):1.

[0046] According to the present invention, it is preferred to react a mixture of a vanadium source, a precipitant and a composite dispersant in a micro-scale confined space to obtain a vanadium dioxide precursor. The reaction is preferably carried out after the pH of the mixture of the vanadium source, the precipitant and the composite dispersant is stabilized. The present invention preferably carries out the above reaction in a rotating liquid film reactor, so that the reaction is carried out in a microscopically uniform environment, thereby ensuring that the nucleation process is controllable.

[0047] In the present invention, the reaction temperature is 40-100° C., preferably 50-80° C.; the reaction time is 10-120 min, preferably 30-100 min.

[0048] After the reaction is completed, the obtained vanadium dioxide precursor is subjected to heat treatment in an inert atmosphere to obtain nano vanadium dioxide.

[0049] In some preferred embodiments of the present invention, after obtaining the vanadium dioxide precursor, it is preferably subjected to washing, filtering, drying and grinding steps, and then heat treatment.

[0050] The present invention has no particular limitation on the above-mentioned washing, filtering and drying processes, which can be carried out according to technical means well known to those skilled in the art.

[0051] In some embodiments of the present invention, the washing is performed by washing with deionized water and anhydrous ethanol for 1 to 2 times respectively.

[0052] In some embodiments of the present invention, the drying is preferably vacuum drying, and the drying temperature is 50-100° C., preferably 60-80° C., and the drying time is 2-12 h, preferably 4-10 h.

[0053] In the present invention, the heat treatment is preferably carried out in a tube furnace, and the vacuum degree in the furnace is preferably evacuated to 10 -3 ~10 -5 mbar, and then heat-treated at 300-700°C for 1-4 h, preferably at 400-600°C for 2-3 h under the protection of an inert atmosphere to obtain nano vanadium dioxide.

[0054] The present invention has no particular limitation on the inert atmosphere, and the inert atmosphere may be any atmosphere well known to those skilled in the art, such as nitrogen.

[0055] In summary, illustratively, in some specific embodiments of the present invention, nano vanadium dioxide is preferably prepared according to the following method:

[0056] Step 1: testing the pH of the vanadium-containing leaching solution, adding a pH adjuster according to the pH to adjust the pH to 1-5, filtering the vanadium-containing leaching solution after adjusting the pH to obtain a vanadium-containing solution;

[0057] Step 2: Take the vanadium-containing solution obtained in step 1, add it to a container, test the vanadium concentration, and prepare a precipitant solution at a molar ratio of 1:(2~10) between the precipitant concentration and the vanadium concentration of the vanadium-containing solution. Prepare a composite dispersant solution at a molar ratio of 1:(1.5~5) between the composite dispersant concentration and the vanadium concentration of the vanadium-containing solution, the molar ratio of citric acid to the acid catalyst in the composite dispersant is (2~4):1, and the precipitant solution and the composite dispersant solution are added to the rotating liquid film reactor at a volume ratio of (1~4):1 and (0.5~2):1 to the vanadium-containing solution through a pump at a uniform speed. After the solution is added, open the circulation, and after the pH of the reaction slurry is stable, react at 40~100℃ for 10~120 min, filter, and wash with deionized water and anhydrous ethanol 1~2 times respectively, and filter after washing to obtain a vanadium dioxide precursor;

[0058] In this step, if the pH of the reaction slurry is unstable, it will cause rapid nucleation of the powder and the powder particle size will be too large;

[0059] Step 3: Place the vanadium dioxide precursor obtained in step 2 in a vacuum drying oven, dry it at 50-100°C for 2-12 h, grind it after drying, place the dried and ground vanadium dioxide precursor in a tube furnace, and first draw the vacuum degree in the furnace to 10 -3 -10 -5mbar, and then heat treated at 300-700°C for 1-4 h under the protection of nitrogen. After the reaction is completed, nano-vanadium dioxide (in powder form) is obtained.

[0060] The specific reaction principle of the above preparation method is: vanadium ions and composite dispersant and precipitant solution in vanadium-containing leaching solution are passed into a rotating liquid film reactor under an acidic environment. In the microscale liquid film reaction space, the addition of the precipitant causes a change in pH. During the process, the dispersant simultaneously realizes the reduction of pentavalent vanadium and the formation and dispersion of sol-gel. Subsequently, the growth of particles is completed by heating reaction to form precursor particles with smaller particle size and better uniformity. Finally, the crystal transformation is completed by drying and heat treatment to prepare vanadium dioxide nanopowder. The sol-gel method can achieve uniform mixing of raw materials in the liquid phase and form a stable sol system through hydrolysis and condensation chemical reactions, while the rotating liquid film reactor is a confined synthesis technology, which is mainly based on assembling small systems, structures, atoms, molecules or particles, and limiting the nucleation and growth processes through the physical space at the micro-nano scale, and "guided" the growth of materials. Combining the sol-gel method and the rotating liquid film reactor, the vanadium ion morphology transformation and ultrafine particle nucleation and growth can be achieved in one step, realizing the preparation of nanopowders with predetermined structural characteristics, while avoiding the occurrence of product agglomeration. The process method has strong controllability of powder particle size and good dispersibility.

[0061] The present invention also provides nano vanadium dioxide prepared by the above preparation method.

[0062] The test shows that the average particle size of the nano vanadium dioxide is 50-100 nm. It can be seen that the nano vanadium dioxide prepared by the above preparation method has a small particle size and a uniform distribution.

[0063] In summary, the technical solution provided by the present invention solves the problems of large particle size, uneven distribution, complex preparation process, high production cost and low preparation efficiency in the prior art vanadium dioxide preparation method.

[0064] In order to further illustrate the present invention, the following examples are used to explain it in detail. The vanadium-containing leaching solution used in the following examples of the present invention is Panzhihua sodium roasting water leaching solution, and the valence state of the vanadium ions contained therein is pentavalent.

[0065] Example 1

[0066] The pH of the vanadium-containing leachate was tested to be 9.5, and 2 mol / L sulfuric acid solution was added to adjust the pH to 3. The vanadium-containing leachate after pH adjustment was filtered for use. The vanadium concentration was tested to be 22.5 g / L, and an ammonium carbonate solution was prepared according to a molar ratio of 1:2 to the vanadium concentration in the vanadium-containing leachate. A composite dispersant solution was prepared according to a molar ratio of 1:1.5 to the vanadium concentration in the vanadium-containing leachate. The composite dispersant included citric acid and acid catalyst nitric acid, and the molar ratio of the two was 2:1. The prepared precipitant solution and composite dispersant solution were uniformly added to the rotating liquid film reactor by a pump at a volume ratio of 4:1 and 2:1 to the vanadium-containing leachate. After the solution was added, the circulation was opened. After the pH of the reaction slurry was stabilized, it was reacted at 80°C for 30 min and then filtered. It was washed once with deionized water and anhydrous ethanol respectively, and filtered after washing to obtain a vanadium dioxide precursor. The vanadium dioxide precursor was placed in a vacuum drying oven and dried at 60 °C for 8 h. After drying, the dried and ground vanadium dioxide precursor was placed in a tube furnace and the vacuum degree in the furnace was first pumped to 10 -5 mbar, and then heat treated at 700℃ for 1.5 h under nitrogen protection. After the reaction, vanadium dioxide nanopowder was obtained, and its SEM image is as follows: Figure 1 shown.

[0067] exist Figure 1 Based on the statistical analysis, the average particle size of the vanadium dioxide nanopowder obtained in Example 1 is 50-100 nm.

[0068] Example 2

[0069] The pH of the vanadium-containing leachate was tested to be 9.5, and 2 mol / L sulfuric acid solution was added to adjust the pH to 1. The vanadium-containing leachate after pH adjustment was filtered for use. The vanadium concentration was tested to be 22.5 g / L, and a sodium carbonate solution was prepared according to a molar ratio of 1:5 to the vanadium concentration of the vanadium-containing leachate. A composite dispersant solution was prepared according to a molar ratio of 1:5 to the vanadium concentration of the vanadium-containing leachate. The composite dispersant included citric acid and acid catalyst hydrochloric acid, and the molar ratio of the two was 3:1. The prepared precipitant solution and composite dispersant solution were uniformly added to the rotating liquid film reactor through a pump at a volume ratio of 2:1 and 1:1 to the vanadium-containing leachate. After the solution was added, the circulation was opened. After the pH of the reaction slurry was stabilized, it was reacted at 100°C for 60 min and then filtered. It was washed once with deionized water and anhydrous ethanol respectively, and filtered after washing to obtain a vanadium dioxide precursor. The vanadium dioxide precursor was placed in a vacuum drying oven and dried at 60 °C for 12 h. After drying, the dried and ground vanadium dioxide precursor was placed in a tube furnace and the vacuum degree in the furnace was first pumped to 10 -3 mbar, and then heat treated at 500 °C for 1 h under nitrogen protection, and vanadium dioxide nanopowder was obtained after the reaction was completed.

[0070] Example 3

[0071] The pH of the vanadium-containing leachate was tested to be 9.5, and 2 mol / L sulfuric acid solution was added to adjust the pH to 1. The vanadium concentration was tested to be 22.5 g / L. Sodium hydroxide solution was prepared according to a molar ratio of 1:10 to the vanadium concentration of the vanadium-containing leachate. A composite dispersant solution was prepared according to a molar ratio of 1:5 to the vanadium concentration of the vanadium-containing leachate. The molar ratio of the composite dispersant citric acid and the acid catalyst hydrochloric acid was 4:1. The prepared precipitant solution and composite dispersant solution were added to the rotating liquid film reactor at a volume ratio of 1:1 and 0.5:1 to the vanadium-containing leachate through a pump at a uniform speed. After the solution was added, the circulation was opened. After the pH of the reaction slurry was stabilized, it was reacted at 40°C for 120 minutes and then filtered. It was washed twice with deionized water and anhydrous ethanol respectively, and then filtered to obtain a vanadium dioxide precursor. The vanadium dioxide precursor was placed in a vacuum drying oven, dried at 60°C for 8 h, and ground after drying. The dried and ground vanadium dioxide precursor was placed in a tubular furnace, and the vacuum degree in the furnace was first drawn to 10 -5 mbar, and then heat treated at 300 °C for 4 h under nitrogen protection to obtain vanadium dioxide nanopowder.

[0072] Example 4

[0073] The pH of the vanadium-containing leachate was tested to be 9.5, and 2 mol / L sulfuric acid solution was added to adjust the pH to 5. The vanadium concentration was tested to be 30 g / L. Sodium bicarbonate solution was prepared at a molar ratio of 1:8 to the vanadium concentration of the vanadium-containing leachate. A composite dispersant solution was prepared at a molar ratio of 1:4 to the vanadium concentration of the vanadium-containing leachate. The composite dispersant included citric acid and acid catalyst acetic acid, and the molar ratio of the two was 3:1. The prepared precipitant solution and composite dispersant solution were added to the rotating liquid film reactor at a volume ratio of 1:1 and 0.5:1 to the vanadium-containing leachate through a pump at a uniform speed. After the solution was added, the circulation was opened. After the pH of the reaction slurry was stabilized, it was reacted at 80°C for 60 min and then filtered. It was washed once with deionized water and anhydrous ethanol respectively, and then filtered to obtain a vanadium dioxide precursor after washing. The vanadium dioxide precursor was placed in a vacuum drying oven, dried at 80°C for 6 h, and ground after drying. The dried and ground vanadium dioxide precursor was placed in a tubular furnace, and the vacuum degree in the furnace was first drawn to 10 -3 mbar, and then heat treated at 550°C for 1.5 h under nitrogen protection, to obtain vanadium dioxide nanopowder after the reaction was completed.

[0074] Through SEM characterization and statistical analysis, it was found that the average particle size of the vanadium dioxide nanopowders obtained in Examples 2 to 4 was 50 to 100 nm.

[0075] Comparative Example 1

[0076] The pH of the vanadium-containing leachate was tested to be 9.5, and 2 mol / L sulfuric acid solution was added to adjust the pH to 3. The vanadium-containing leachate after pH adjustment was filtered for use. The vanadium concentration was tested to be 22.5 g / L. An ammonium carbonate solution was prepared according to a molar ratio of 1:2 to the vanadium concentration in the vanadium-containing leachate. A citric acid solution was prepared according to a molar ratio of 1:1.5 to the vanadium concentration in the vanadium-containing leachate. The prepared precipitant solution and citric acid solution were added to the rotating liquid film reactor at a volume ratio of 4:1 and 2:1 to the vanadium-containing leachate through a pump at a uniform speed. After the solution was added, the circulation was opened. After the pH of the reaction slurry was stabilized, it was reacted at 80°C for 30 min and then filtered. It was washed once with deionized water and anhydrous ethanol respectively, and filtered after washing to obtain a vanadium dioxide precursor. The vanadium dioxide precursor was placed in a vacuum drying oven, dried at 60°C for 8 h, and ground after drying. The dried and ground vanadium dioxide precursor was placed in a tubular furnace, and the vacuum degree in the furnace was first drawn to 10 -5 mbar, and then heat treated at 700°C for 1.5 h under the protection of nitrogen. After the reaction, the nanopowder obtained was a mixture of vanadium dioxide and vanadium pentoxide.

[0077] Comparative Example 2

[0078] The pH of the vanadium-containing leachate was tested to be 9.5, and 2 mol / L sulfuric acid solution was added to adjust the pH to 3. The vanadium-containing leachate after pH adjustment was filtered for use. The vanadium concentration was tested to be 22.5 g / L, and an ammonium carbonate solution was prepared according to a molar ratio of 1:2 to the vanadium concentration in the vanadium-containing leachate. A composite dispersant solution was prepared according to a molar ratio of 1:1.5 to the vanadium concentration in the vanadium-containing leachate. The composite dispersant included citric acid and acid catalyst nitric acid, and the molar ratio of the two was 2:1. The prepared precipitant solution and composite dispersant solution were uniformly added to the reaction vessel through a pump at a volume ratio of 4:1 and 2:1 to the vanadium-containing leachate. After the solution was added, the circulation was opened. After the pH of the reaction slurry was stabilized, it was reacted at 80°C for 30 min and then filtered. It was washed once with deionized water and anhydrous ethanol respectively, and filtered after washing to obtain a vanadium dioxide precursor. The vanadium dioxide precursor was placed in a vacuum drying oven and dried at 60°C for 8 hours. After drying, the dried and ground vanadium dioxide precursor was placed in a tube furnace and the vacuum degree in the furnace was first pumped to 10 -5 mbar, and then heat treated at 700 °C for 1.5 h under nitrogen protection. After the reaction was completed, vanadium dioxide nanopowders with a size of 300-400 nm were obtained.

[0079] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing nano vanadium dioxide, characterized in that: The following steps are involved: S1: Mixing the vanadium source with the precipitant and the composite dispersant in an acidic environment, and reacting in a microscale confined space to obtain a vanadium dioxide precursor; The composite dispersant comprises citric acid and an acid catalyst, wherein the acid catalyst is selected from any one or more of nitric acid, acetic acid or hydrochloric acid; S2: heat-treating the vanadium dioxide precursor in an inert atmosphere to obtain nano-vanadium dioxide.

2. The method for preparing nano vanadium dioxide according to claim 1, characterized in that: The molar ratio of the citric acid to the acid catalyst is (2-4):

1.

3. The method for preparing nano vanadium dioxide according to claim 1 or 2, characterized in that: The vanadium source is a vanadium-containing leaching solution; The precipitant is selected from any one or more of ammonium carbonate, sodium carbonate, sodium hydroxide or sodium bicarbonate.

4. The method for preparing nano vanadium dioxide according to any one of claims 1 to 3, characterized in that: The precipitant and the composite dispersant are mixed with the vanadium source in the form of a precipitant solution and a composite dispersant solution respectively; The molar ratio of the concentration of the precipitant solution to the vanadium concentration in the vanadium source is 1:(2-10); The molar ratio of the concentration of the composite dispersant solution to the vanadium concentration in the vanadium source is 1:(1.5-5).

5. The method for preparing nano vanadium dioxide according to claim 4, characterized in that: The volume ratio of the precipitant solution, the composite dispersant solution and the vanadium source is (4-1):(2-0.5):

1.

6. The method for preparing nano vanadium dioxide according to any one of claims 1 to 5, characterized in that: The pH of the acidic environment is 1-5.

7. The method for preparing nano vanadium dioxide according to any one of claims 1 to 6, characterized in that: The reaction temperature is 40-100°C and the reaction time is 10-120 min; The reaction is carried out in a rotating liquid film reactor.

8. The method for preparing nano vanadium dioxide according to any one of claims 1 to 7, characterized in that: After the reaction is completed, the steps of washing, filtering and drying are also included; The method further comprises a grinding step before the heat treatment.

9. The method for preparing nano vanadium dioxide according to any one of claims 1 to 8, characterized in that: The heat treatment temperature is 300-700°C and the time is 1-4 h.

10. The nano vanadium dioxide prepared by the method for preparing nano vanadium dioxide according to any one of claims 1 to 9, characterized in that: The average particle size of the nano vanadium dioxide is 50-100 nm.

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