Preparation method of superfine tungsten trioxide

Abstract

The application provides a preparation method of superfine tungsten trioxide, which comprises the following steps: dissolving an ammonium tungstate salt in ammonia water to obtain an ammonium tungstate salt solution; adding hydrogen peroxide and an organic complexing agent into the ammonium tungstate salt solution, stirring and reacting to obtain a precursor solution; performing ultrasonic atomization and spray pyrolysis on the precursor solution, performing gas-solid separation on a pyrolysis product, and collecting a solid powder; and performing annealing treatment on the solid powder to obtain superfine tungsten trioxide. By adding hydrogen peroxide and an organic complexing agent into the ammonia water solution of the ammonium tungstate salt, a peroxotungstic acid precursor solution with high stability and high dispersity is constructed; by means of ultrasonic atomization and spray pyrolysis process, the micron-sized droplet pyrolysis process is rapidly completed; the crystallinity of the pyrolysis product can be further improved under annealing treatment; and finally, the prepared superfine tungsten trioxide powder has high specific surface area, narrow particle size distribution and good crystal phase purity.

Description

Technical Field

[0001] This invention relates to the field of tungsten trioxide preparation technology, and specifically to a method for preparing ultrafine tungsten trioxide. Background Technology

[0002] Tungsten trioxide (WO3), as an important functional material, has broad application prospects in photocatalysis, electrochromic devices, gas sensors, lithium-ion battery anode materials, and superhard alloy additives. With the continuous expansion of downstream high-end applications, increasingly higher requirements are being placed on the particle size, purity, morphology, and particle size distribution of tungsten oxide powder.

[0003] Currently, the mainstream method for preparing tungsten oxide powder in industry is the direct calcination method of ammonium paratungstate (APT), which involves decomposing APT in a rotary kiln at 400-700℃ to obtain tungsten oxide. Although this method has a relatively short process flow, it has the following shortcomings: (1) the grains tend to grow during the calcination process, making it difficult to stably obtain ultrafine powders below 100nm; (2) the product has a wide particle size distribution and irregular particle morphology; (3) the high-temperature calcination consumes a lot of energy; and (4) the product often needs to undergo post-processing steps such as crushing and sieving, which can easily introduce impurities.

[0004] In addition, existing technologies have reported the preparation of nano-tungsten oxide using chemical methods (such as sol-gel and hydrothermal methods), but these methods typically involve long processes, low production efficiency, and are difficult to scale up for continuous industrial production. Spray pyrolysis, as an aerosol process, uses a liquid-phase solution as a precursor and combines many advantages of both gas-phase and liquid-phase methods: simple process, rapid reaction, and products with regular spherical shapes and minimal agglomeration. Previous studies have attempted to apply spray pyrolysis technology to the preparation of tungsten oxide. However, existing methods for preparing tungsten oxide using spray pyrolysis still suffer from technical problems such as insufficient stability of the precursor solution, low product crystallinity, and the need to improve particle size uniformity. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present invention provides a method for preparing ultrafine tungsten trioxide, which aims to solve the technical problem that existing tungsten trioxide preparation methods are difficult to obtain ultrafine tungsten trioxide powder with small particle size, narrow distribution and good crystallinity.

[0006] In a first aspect, the present invention provides a method for preparing ultrafine tungsten trioxide, comprising the following steps: S1. Dissolve ammonium tungstate in ammonia water to obtain an ammonium tungstate solution; add hydrogen peroxide and an organic complexing agent to the ammonium tungstate solution, stir and react to obtain a precursor solution; S2. The precursor solution is subjected to ultrasonic atomization and spray pyrolysis, and the pyrolysis products are separated into gas and solid, and the solid powder is collected. S3. Anneal the solid powder to obtain ultrafine tungsten trioxide.

[0007] Preferably, the pH of the ammonium tungstate solution is 8-9; the concentration of the ammonium tungstate solution, calculated as W, is 0.1-2.0 mol / L.

[0008] Preferably, the ammonium tungstate salt is selected from at least one of ammonium tungstate, ammonium paratungstate, and ammonium metatungstate.

[0009] Preferably, the organic complexing agent includes at least one of citric acid, oxalic acid, and ethylenediaminetetraacetic acid; the molar ratio of the organic complexing agent to the tungsten element in the ammonium tungstate solution is (0.5~2):1.

[0010] Preferably, the molar ratio of H2O2 in hydrogen peroxide to tungsten in ammonium tungstate solution is (5~30):1.

[0011] Preferably, in step S1, the temperature of the stirring reaction is 20~60℃, and the stirring reaction time is 1~4 hours.

[0012] Preferably, in step S2, the conditions for ultrasonic atomization are: ultrasonic frequency of 1~3MHz and compressed air pressure of 1-5bar for the atomizing nozzle.

[0013] Preferably, in step S2, the conditions for spray pyrolysis are: pyrolysis temperature of 300~700℃, pyrolysis time of 0.5-5s, and pyrolysis atmosphere including at least one of air, oxygen or inert gas.

[0014] Preferably, in step S3, the annealing conditions are: annealing temperature of 200~500℃ and holding time of 1~6 hours.

[0015] Secondly, the present invention provides an ultrafine tungsten trioxide, which is prepared by the method described in one aspect of the present invention.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method for preparing ultrafine tungsten trioxide provided by the present invention constructs a highly stable and highly dispersible peroxytungstic acid precursor solution by adding hydrogen peroxide and an organic complexing agent to an ammonia solution of ammonium tungstate salt; the micron-level droplet pyrolysis process is rapidly completed by ultrasonic atomization and spray pyrolysis process, and the crystallinity of the pyrolysis product can be further improved by annealing treatment. The final ultrafine tungsten trioxide powder has a high specific surface area, narrow particle size distribution and good crystal phase purity.

[0017] (2) The preparation method of ultrafine tungsten trioxide provided by the present invention has a short process flow and high efficiency. The pyrolysis reaction is completed within a few seconds, avoiding the introduction of impurities and abnormal growth of grains.

[0018] (3) The preparation method provided by the present invention is green and environmentally friendly, does not involve high temperature and long-term calcination, and has low energy consumption; the tail gas is mainly water vapor and a small amount of ammonia, which is easy to treat. Attached Figure Description

[0019] Figure 1 The image shows the XRD pattern of tungsten oxide prepared in Example 1 of this invention. Figure 2 The image shows the XRD pattern of tungsten oxide prepared in Comparative Example 4 of this invention. Detailed Implementation

[0020] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0021] To address the technical problem of obtaining ultrafine tungsten trioxide powder with small particle size, narrow distribution, and good crystallinity using existing tungsten oxide preparation methods, this invention provides a method for preparing ultrafine tungsten trioxide. By optimizing the composition of the precursor solution, controlling the spray pyrolysis process parameters, and combining it with an annealing heat treatment process, particle agglomeration and abnormal grain growth are effectively suppressed, thereby achieving controllable preparation of ultrafine tungsten trioxide powder.

[0022] In a first aspect, embodiments of the present invention provide a method for preparing ultrafine tungsten trioxide, comprising the following steps: S1. Dissolve ammonium tungstate in ammonia water to obtain an ammonium tungstate solution; add hydrogen peroxide and an organic complexing agent to the ammonium tungstate solution, stir and react to obtain a precursor solution; S2. The precursor solution is subjected to ultrasonic atomization and spray pyrolysis, and the pyrolysis products are separated into gas and solid, and the solid powder is collected. S3. Anneal the solid powder to obtain ultrafine tungsten trioxide.

[0023] In the technical solution of this invention embodiment, the principle is as follows: Ammonia water first dissolves ammonium tungstate salt, making the solution weakly alkaline. Then, when hydrogen peroxide is added, the alkaline environment helps the formation of peroxytungstate complex and may release a small amount of ammonia gas, further regulating the microenvironment of the solution. The organic complexing agent chelates with tungsten ions under weakly alkaline conditions, forming steric hindrance and inhibiting particle aggregation, thereby obtaining a uniform and stable precursor solution. During the spray pyrolysis process, the precursor solution is ultrasonically atomized to form micron-sized droplet aerosols, which then undergo pyrolysis. Ammonium peroxytungstate decomposes to produce a large amount of gas and simultaneously forms ultrafine tungsten trioxide powder. After annealing, the crystallinity of the product is further improved.

[0024] Furthermore, in some embodiments, the pH of the ammonium tungstate solution is 8-9; the concentration of the ammonium tungstate solution, calculated as W, is 0.1-2.0 mol / L.

[0025] Furthermore, in some embodiments, the ammonium tungstate salt is selected from at least one of ammonium tungstate, ammonium paratungstate, and ammonium metatungstate; the ammonium tungstate salt has high solubility in ammonia water, which helps to prepare a uniform and stable precursor solution and prevents premature precipitation of tungstic acid.

[0026] Furthermore, in some embodiments, the organic complexing agent includes at least one of citric acid, oxalic acid, and ethylenediaminetetraacetic acid; the molar ratio of the organic complexing agent to the tungsten element in the ammonium tungstate solution is (0.5~2):1.

[0027] In the technical solution of this invention embodiment, the organic complexing agent forms a stable peroxytungstate complex with tungsten ions in a weakly alkaline environment provided by ammonia water.

[0028] Furthermore, in some embodiments, the molar ratio of H2O2 in hydrogen peroxide to tungsten in ammonium tungstate solution is (5~30):1.

[0029] In the technical solution of this invention embodiment, hydrogen peroxide is used in excess to ensure that tungsten elements fully form soluble peroxytungstate complexes and to avoid the generation of impurity phases during the pyrolysis of the precursor due to incomplete oxidation.

[0030] Furthermore, in some embodiments, in step S1, the temperature of the stirring reaction is 20~60°C, and the stirring reaction time is 1~4 hours; to ensure that a stable peroxytungstate complex is formed in the precursor solution, and a homogeneous and stable precursor solution is obtained.

[0031] Furthermore, in some embodiments, in step S2, the conditions for ultrasonic atomization are: ultrasonic frequency of 1~3MHz, compressed air pressure of the atomizing nozzle of 1-5bar; the conditions for spray pyrolysis are: pyrolysis temperature of 300~700℃, pyrolysis time of 0.5-5s, and pyrolysis atmosphere including at least one of air, oxygen or inert gas.

[0032] Furthermore, in some embodiments, in step S2, the gas-solid separation device includes a cyclone separator or a bag filter.

[0033] Furthermore, in some embodiments, in step S3, the annealing conditions are: annealing temperature of 200~500℃ and holding time of 1~6 hours.

[0034] Secondly, embodiments of the present invention provide an ultrafine tungsten trioxide, which is prepared by the ultrafine tungsten trioxide preparation method described in one aspect.

[0035] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0036] Example 1 A method for preparing ultrafine tungsten trioxide, the specific steps of which are as follows: (1) Dissolve ammonium metatungstate (AMT) in an ammonia solution, adjust the pH to 8-9, and prepare a 0.5 mol / L (W) ammonium tungstate salt solution. Add H2O2 (H2O2:W molar ratio of 15:1) and citric acid (CA:W molar ratio of 1.0:1) to the ammonium tungstate salt solution and stir the reaction at 40℃ for 2 h to obtain the precursor solution.

[0037] (2) The precursor solution is ultrasonically atomized at a frequency of 2.0 MHz and the compressed air pressure of the atomizing nozzle is 2.5 bar to obtain micron-sized droplet aerosols; the aerosols are sent into a spray pyrolysis furnace for pyrolysis at 500°C for 2 s and the pyrolysis atmosphere is air; the gas-solid mixture after pyrolysis is separated by a bag filter and the solid powder is collected.

[0038] (3) The solid powder was annealed at 350°C for 1 hour to obtain ultrafine tungsten trioxide.

[0039] Example 2 A method for preparing ultrafine tungsten trioxide, the specific steps of which are as follows: (1) Dissolve ammonium paratungstate (APT) in an ammonia solution, adjust the pH to 8-9, and prepare a 1.2 mol / L (W) ammonium tungstate salt solution. Add H2O2 (H2O2:W molar ratio of 20:1) and PEG-400 (PEG:W molar ratio of 0.8:1) to the ammonium tungstate salt solution and stir the reaction at 55℃ for 3 h to obtain the precursor solution.

[0040] (2) The precursor solution was ultrasonically atomized at a frequency of 2.5 MHz and the compressed air pressure of the atomizing nozzle was 3 bar to obtain micron-sized droplet aerosols. The aerosols were sent into a spray pyrolysis furnace for pyrolysis at 600°C for 1.5 s and the pyrolysis atmosphere was oxygen. The gas-solid mixture after pyrolysis was separated by a bag filter and the solid powder was collected.

[0041] (3) The solid powder was annealed at 400℃ for 1 hour to obtain ultrafine tungsten trioxide.

[0042] Example 3 A method for preparing ultrafine tungsten trioxide, the specific steps of which are as follows: (1) Dissolve ammonium tungstate in ammonia solution, adjust the pH to 8-9, and prepare a 0.5 mol / L (W) ammonium tungstate salt solution. Add H2O2 (H2O2:W molar ratio of 8:1) and ethylenediaminetetraacetic acid (EDTA) (EDTA:W molar ratio of 1.5:1) to the ammonium tungstate salt solution and stir the reaction at 25℃ for 4 h to obtain the precursor solution.

[0043] (2) The precursor solution was ultrasonically atomized at a frequency of 1.5 MHz and the compressed air pressure of the atomizing nozzle was 4.0 bar to obtain micron-sized droplet aerosols. The aerosols were sent into a spray pyrolysis furnace for pyrolysis at 400°C for 3 s and the pyrolysis atmosphere was oxygen. The gas-solid mixture after pyrolysis was separated by a bag filter and the solid powder was collected.

[0044] (3) The solid powder was annealed at 250°C for 1 hour to obtain ultrafine tungsten trioxide.

[0045] Comparative Example 1 The difference between this comparative example and Example 1 is that the ammonia solution is replaced with deionized water. The specific steps are as follows: (1) Dissolve ammonium metatungstate (AMT) in deionized water without adjusting the pH to prepare a 0.5 mol / L (W) ammonium tungstate salt solution. Add H2O2 (H2O2:W molar ratio of 15:1) and citric acid (CA:W molar ratio of 1.0:1) to the ammonium tungstate salt solution and stir at 40℃ for 2 h to obtain the precursor solution.

[0046] (2) The precursor solution is ultrasonically atomized at a frequency of 2.0 MHz and the compressed air pressure of the atomizing nozzle is 2.5 bar to obtain micron-sized droplet aerosols; the aerosols are sent into a spray pyrolysis furnace for pyrolysis at 500°C for 2 s and the pyrolysis atmosphere is air; the gas-solid mixture after pyrolysis is separated by a bag filter and the solid powder is collected.

[0047] (3) The solid powder was annealed at 350°C for 1 h to obtain tungsten trioxide powder.

[0048] Comparative Example 2 The difference between this comparative example and Example 1 is that the addition of citric acid complexing agent is omitted. The specific steps are as follows: (1) Dissolve ammonium metatungstate (AMT) in an ammonia solution, adjust the pH to 8-9, and prepare a 0.5 mol / L (W) ammonium tungstate salt solution. Add H2O2 (H2O2:W molar ratio of 15:1) to the ammonium tungstate salt solution and stir the reaction at 40℃ for 2 h to obtain the precursor solution.

[0049] (2) The precursor solution is ultrasonically atomized at a frequency of 2.0 MHz and the compressed air pressure of the atomizing nozzle is 2.5 bar to obtain micron-sized droplet aerosols; the aerosols are sent into a spray pyrolysis furnace for pyrolysis at 500°C for 2 s and the pyrolysis atmosphere is air; the gas-solid mixture after pyrolysis is separated by a bag filter and the solid powder is collected.

[0050] (3) The solid powder was annealed at 350°C for 1 h to obtain tungsten trioxide powder.

[0051] Comparative Example 3 The difference between this comparative example and Example 1 is that the ultrasonic spray frequency is 0.5MHz, and the specific steps are as follows: (1) Dissolve ammonium metatungstate (AMT) in an ammonia solution, adjust the pH to 8-9, and prepare a 0.5 mol / L (W) ammonium tungstate salt solution. Add H2O2 (H2O2:W molar ratio of 15:1) and citric acid (CA:W molar ratio of 1.0:1) to the ammonium tungstate salt solution and stir the reaction at 40℃ for 2 h to obtain the precursor solution.

[0052] (2) The precursor solution is ultrasonically atomized at a frequency of 0.5 MHz and the compressed air pressure of the atomizing nozzle is 2.5 bar to obtain micron-sized droplet aerosols; the aerosols are sent into a spray pyrolysis furnace for pyrolysis at 500°C for 2 s and the pyrolysis atmosphere is air; the gas-solid mixture after pyrolysis is separated by a bag filter and the solid powder is collected.

[0053] (3) The solid powder was annealed at 350°C for 1 hour to obtain tungsten trioxide powder.

[0054] Comparative Example 4 The difference between this comparative example and Example 1 is that the pyrolysis products were collected directly without the annealing treatment in step (3). The specific steps are as follows: (1) Dissolve ammonium metatungstate (AMT) in an ammonia solution, adjust the pH to 8-9, and prepare a 0.5 mol / L (W) ammonium tungstate salt solution. Add H2O2 (H2O2:W molar ratio of 15:1) and citric acid (CA:W molar ratio of 1.0:1) to the ammonium tungstate salt solution and stir the reaction at 40℃ for 2 h to obtain the precursor solution.

[0055] (2) The precursor solution is ultrasonically atomized at a frequency of 2.0 MHz and the compressed air pressure of the atomizing nozzle is 2.5 bar to obtain micron-sized droplet aerosols; the aerosols are sent into a spray pyrolysis furnace for pyrolysis at 500°C for 2 s and the pyrolysis atmosphere is air; the gas-solid mixture after pyrolysis is separated by a bag filter and the solid powder is collected to obtain tungsten trioxide powder.

[0056] Comparative Example 5 The difference between this comparative example and Example 1 is that the annealing temperature was increased from 350°C to 700°C. The specific steps are as follows: (1) Dissolve ammonium metatungstate (AMT) in an ammonia solution, adjust the pH to 8-9, and prepare a 0.5 mol / L (W) ammonium tungstate salt solution. Add H2O2 (H2O2:W molar ratio of 15:1) and citric acid (CA:W molar ratio of 1.0:1) to the ammonium tungstate salt solution and stir the reaction at 40℃ for 2 h to obtain the precursor solution.

[0057] (2) The precursor solution is ultrasonically atomized at a frequency of 2.0 MHz and the compressed air pressure of the atomizing nozzle is 2.5 bar to obtain micron-sized droplet aerosols; the aerosols are sent into a spray pyrolysis furnace for pyrolysis at 500°C for 2 s and the pyrolysis atmosphere is air; the gas-solid mixture after pyrolysis is separated by a bag filter and the solid powder is collected.

[0058] (3) The solid powder was annealed at 700℃ for 1h to obtain ultrafine tungsten trioxide.

[0059] Performance testing: The physicochemical properties of the tungsten trioxide powders prepared in Examples 1-3 and Comparative Examples 1-5 were characterized. Specific surface area was determined using the BET nitrogen adsorption method, and particle size distribution was determined using a laser particle size analyzer. The test results are shown in Table 1 below.

[0060] Table 1

[0061] Table 1 shows that the tungsten trioxide powder prepared in the embodiments of the present invention has a high specific surface area, a narrow particle size distribution, and good crystallinity after appropriate annealing. The XRD pattern of the tungsten trioxide powder prepared in Example 1 of the present invention is shown below. Figure 1 As shown.

[0062] In Comparative Example 1, the ammonium metatungstate solution is a weakly acidic environment. The precursor solution has poor stability and is prone to local precipitation. It is also prone to agglomeration during spray pyrolysis, resulting in powders with low specific surface area and wide particle size distribution.

[0063] Comparative Example 2, due to the lack of citric acid complexing agent, resulted in poor dispersibility of the precursor solution, severe agglomeration, and a sharp increase in average particle size.

[0064] Comparative Example 3 showed that due to the excessively low ultrasonic frequency, the atomized droplets were too large, resulting in coarse particles after pyrolysis.

[0065] Comparative Example 4, although possessing a high specific surface area and small particle size, exhibited poor XRD analysis (e.g., Figure 2 As shown in the figure, its crystallinity is significantly low, making it difficult to meet the requirements of high-end applications for material structural stability.

[0066] Although Comparative Example 5 underwent high-temperature annealing, the excessively high annealing temperature led to grain growth and densification, causing the specific surface area to plummet to 4.33 m². 2 / g is no longer sufficient to meet the requirements of ultrafine powders for high specific surface area.

[0067] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for preparing ultrafine tungsten trioxide, characterized in that, Includes the following steps: S1. Dissolve ammonium tungstate in ammonia water to obtain an ammonium tungstate solution; add hydrogen peroxide and an organic complexing agent to the ammonium tungstate solution, stir and react to obtain a precursor solution; S2. The precursor solution is subjected to ultrasonic atomization and spray pyrolysis, and the pyrolysis products are subjected to gas-solid separation to collect solid powder. S3. Anneal the solid powder to obtain ultrafine tungsten trioxide.

2. The method for preparing ultrafine tungsten trioxide according to claim 1, characterized in that, The pH of the ammonium tungstate solution is 8-9; And / or, the concentration of the ammonium tungstate solution is 0.1~2.0 mol / L based on W element.

3. The method for preparing ultrafine tungsten trioxide according to claim 1, characterized in that, The ammonium tungstate salt is selected from at least one of ammonium tungstate, ammonium paratungstate, and ammonium metatungstate.

4. The method for preparing ultrafine tungsten trioxide according to claim 1, characterized in that, The organic complexing agent includes at least one of citric acid, oxalic acid, and ethylenediaminetetraacetic acid; And / or, the molar ratio of the organic complexing agent to the tungsten element in the ammonium tungstate solution is (0.5~2):

1.

5. The method for preparing ultrafine tungsten trioxide according to claim 1, characterized in that, The molar ratio of H2O2 in the hydrogen peroxide to tungsten in the ammonium tungstate solution is (5~30):

1.

6. The method for preparing ultrafine tungsten trioxide according to claim 1, characterized in that, In step S1, the temperature of the stirring reaction is 20~60℃, and the stirring reaction time is 1~4 hours.

7. The method for preparing ultrafine tungsten trioxide according to claim 1, characterized in that, In step S2, the conditions for ultrasonic atomization are: ultrasonic frequency of 1~3MHz and compressed air pressure of 1-5bar for the atomizing nozzle.

8. The method for preparing ultrafine tungsten trioxide according to claim 1, characterized in that, In step S2, the conditions for spray pyrolysis are: pyrolysis temperature of 300~700℃, pyrolysis time of 0.5-5s, and pyrolysis atmosphere including at least one of air, oxygen or inert gas.

9. The method for preparing ultrafine tungsten trioxide according to claim 1, characterized in that, In step S3, the annealing conditions are: annealing temperature of 200~500℃ and holding time of 1~6 hours.

10. An ultrafine tungsten trioxide, characterized in that, It is prepared by the preparation method of ultrafine tungsten trioxide according to any one of claims 1 to 9.

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