Tungsten oxide quantum dot and preparation method and application thereof

Abstract

The invention provides a tungsten oxide quantum dot and a preparation method and application thereof. The preparation method comprises the steps that an acid solution serves as an electrolyte, metal tungsten or tungsten-containing alloy serves as an anode, an electrolytic reaction is conducted under the action of voltage, the tungsten oxide quantum dots are prepared, the electrolyte is a low-concentration sulfuric acid or hydrochloric acid solution, and an inert electrode material serves as a cathode; the tungsten oxide quantum dots with the particle size range of 2-20 nm, extremely narrow particle size distribution and good monodispersity are obtained through electrolytic reaction under direct-current voltage, and particularly, the batch yield of the quantum dots can reach the gram level. The quantum dot has good electrochromic performance and is suitable for the fields of flexible display devices, intelligent windows, photocatalysis and the like.

Description

Technical Field

[0001] This invention relates to the field of quantum dot materials technology, specifically to a tungsten oxide quantum dot, its preparation method and application, and more specifically, to a method for controllably preparing tungsten oxide quantum dots using an electrochemical method and its application in fields such as smart windows and flexible display devices. Background Technology

[0002] Tungsten oxide quantum dots (WO3 QDs), as a wide-bandgap (2.4-3.6 eV) n-type semiconductor nanomaterials with significant quantum size and surface effects, have shown great application potential in high-tech fields such as smart windows, environmental remediation, new energy storage, and biosensing due to their unique tunable optical bandgap, rapid interfacial charge transfer characteristics, and excellent photoelectrochemical performance. However, current mainstream preparation techniques still face many technical bottlenecks. For example, while the hot-injection method can achieve bottom-up synthesis with controllable morphology and size, it suffers from low yield (usually milligram-level), severe organic ligand contamination, and complex subsequent purification. Although the solvothermal method can prepare well-crystallized tungsten oxide quantum dots, it requires harsh high-temperature and high-pressure conditions (usually exceeding 180°C), which not only consumes a lot of energy and requires strict equipment, but more importantly, it is difficult to precisely control the kinetics of nucleation and growth during the reaction, resulting in uneven particle size distribution (10-50 nm) and poor monodispersity (PDI>0.3). Qingqing Liu et al. (Hydrothermal synthesis of oxygen-deficiency tungsten oxide quantum dots with excellent photochromicreversibility, Applied Surface Science , 480 (2019) 404–409) successfully synthesized WO3 using a simplified hydrothermal method. 3-x Nanoparticles were purified by a hydrothermal reaction of ammonium tungstate, polyvinylpyrrolidone (PVP), and oxalic acid at a constant temperature of 180°C, followed by drying to obtain a pale yellow WO3. 3-x Quantum dot powder with a narrow particle size distribution of 2-9 nm, indicating that the ultra-small WO3 particles... 3-x Quantum dots have a greater advantage in photochromic applications. However, although the above method can obtain quantum dots with a narrow distribution, the yield is very low, usually only in the milligram range. Therefore, this method is extremely difficult to promote and apply on a large scale in industrialization.

[0003] Based on this, the present invention proposes a method for preparing tungsten oxide quantum dots based on a milder and more efficient electrolysis method. This method can achieve the controllable synthesis of tungsten oxide quantum dots under ambient temperature and pressure conditions. By precisely controlling the electrolysis parameters (voltage, electrolyte composition, etc.), it is not only simple to operate and environmentally friendly, but also enables gram-scale mass production. Moreover, the obtained quantum dots have the characteristic of uniform size and can achieve the preparation of quantum dots with an extremely narrow distribution range of 2~20 nm. Therefore, the technical solution of the present invention provides a new technical path for the industrial application of tungsten oxide quantum dots. Summary of the Invention

[0004] The purpose of this invention is to provide a tungsten oxide quantum dot, its preparation method, and its application, so as to overcome the shortcomings of the prior art.

[0005] To achieve the above objectives, the present invention provides a method for preparing tungsten oxide quantum dots, which employs an electrolytic method, using a low-concentration acidic solution as the electrolyte and metallic tungsten or a tungsten-containing alloy as the anode, and carrying out an electrolytic reaction under voltage to prepare tungsten oxide quantum dots.

[0006] In a preferred embodiment, the electrolyte in the electrolysis method is a low-concentration acidic solution.

[0007] In a preferred embodiment, the electrolyte is hydrochloric acid or sulfuric acid.

[0008] In a preferred embodiment, the concentration of the electrolyte is 0.01~5 mol / L; preferably 2~4 mol / L.

[0009] In a preferred embodiment, the cathode in the electrolysis reaction is an inert electrode material.

[0010] In a preferred embodiment, the inert electrode material is any one of a titanium plate, a platinum electrode, or a graphite electrode; preferably a titanium plate.

[0011] In a preferred embodiment, the anode in the electrolysis reaction is a pure tungsten plate or a tungsten-containing alloy.

[0012] In a preferred embodiment, the tungsten-containing alloy is a tungsten-cobalt alloy or a tungsten-iron-nickel alloy.

[0013] In a preferred embodiment, the tungsten alloy contains ≥70% tungsten by mass.

[0014] In a preferred embodiment, the voltage is a DC voltage or a pulse voltage.

[0015] In a preferred embodiment, the DC voltage is 3~6V; preferably 4~5V.

[0016] In a preferred embodiment, the electrolysis reaction temperature is 20–60 °C. If the temperature is too high, tungsten oxide and sulfuric acid will react; if the temperature is too low, it is not conducive to the formation of quantum dots, and the resulting quantum dots will be too large.

[0017] Preferably, the temperature of the electrolysis reaction is 25~35℃.

[0018] In a preferred embodiment, the electrolysis reaction further includes post-processing.

[0019] In a preferred embodiment, the post-processing includes purifying the electrolysis product and then drying it.

[0020] In a preferred embodiment, the purification process includes washing the electrolysis product alternately with ethanol and deionized water, centrifuging, and finally collecting the purified product.

[0021] In a preferred embodiment, the drying process includes drying the purified product at a temperature of 50-80°C for 2-6 hours to obtain the tungsten oxide quantum dots.

[0022] As one of the objectives of this invention, this invention also provides a tungsten oxide quantum dot, which is prepared using the preparation method described above.

[0023] In a preferred embodiment, the quantum dot size is 2–20 nm.

[0024] For example, taking the effect of DC voltage as an example, when the voltage is 3~4.5V, the particle size range of tungsten oxide quantum dots is 20 nm; when the voltage is 5~6V, the particle size of tungsten oxide quantum dots is about 2~4 nm, and the size of quantum dots becomes significantly larger.

[0025] As one of the objectives of the invention, the present invention also provides an application in the fields of tungsten oxide quantum dot flexible display devices, smart windows, or photocatalysis as described above.

[0026] The beneficial technical effects obtained by this invention are as follows: 1. The technical solution of this invention can achieve the controllable preparation of tungsten oxide quantum dots at room temperature and pressure using a mild electrochemical synthesis method. The synthesis conditions are simple, the operation is convenient, and it is environmentally friendly, making it suitable for large-scale production and application.

[0027] 2. This invention can achieve uniformity in the distribution of quantum dot particle size by adjusting electrolysis parameters, including voltage and electrolyte concentration, and can prepare tungsten oxide quantum dots with extremely narrow particle size distribution, such as 3-4 nm. Moreover, the technical solution of this invention can achieve gram-level production, which not only solves the technical problem of uneven particle size distribution (10-50 nm) of quantum dots generated by traditional methods, but also overcomes the problem of difficulty in scaling up the production scale of tungsten oxide quantum dots, scaling up the existing milligram-level production scale to the gram level.

[0028] 3. The present invention can directly obtain quantum dots without subsequent high-temperature treatment, thus avoiding the problem of quantum dot aggregation. Furthermore, the hydration structure of the quantum dots obtained by the present invention can significantly improve the stability of the material and the density of surface active sites.

[0029] 4. This invention employs gradient centrifugation purification technology to achieve efficient separation of ultra-small quantum dots (2~4 nm), with excellent monodispersity of the product.

[0030] 5. The present invention has the characteristics of simple process, environmental friendliness and high yield in preparing tungsten oxide quantum dots. The yield of a single batch can reach the gram level, which is more than 1,000 times that of the traditional hot injection method (milligram level). It provides a practical and feasible technical solution for the large-scale industrial promotion and production of tungsten oxide quantum dots. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is the XRD pattern of tungsten oxide quantum dots prepared in Example 1 of the present invention.

[0033] Figure 2 This is a TEM image of the tungsten oxide quantum dots prepared in Example 1 of this invention.

[0034] Figure 3 This is a TEM image of the tungsten oxide quantum dots prepared in Example 3 of this invention.

[0035] Figure 4 This is a photograph of the electrochromic electrode prepared from tungsten oxide quantum dots according to Example 1 of the present invention, showing the color change. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0037] Specifically, as one aspect of the technical solution of this invention, the electrochemical preparation method of tungsten oxide quantum dots includes: Using 0.01–5 mol / L sulfuric acid or hydrochloric acid as the electrolyte; using pure tungsten plate or common tungsten-containing hard alloy as the anode and inert electrode material as the cathode; electrolyzing at 3–6 V DC voltage for 0.5–5 hours (20–60 ℃); obtaining tungsten oxide quantum dots after centrifugation, washing, purification, and drying.

[0038] In some preferred embodiments, the preparation method specifically includes: adding sulfuric acid to deionized water to prepare an electrolyte solution of 2-4 mol / L and stirring to ensure thorough mixing.

[0039] Furthermore, the electrolyte concentration can be any one of 2 mol / L, 3 mol / L, and 4 mol / L, preferably 4 mol / L.

[0040] In some preferred embodiments, the preparation method specifically includes: using a pure tungsten plate or a common tungsten-containing hard alloy as the anode and an inert electrode material as the cathode; electrolyzing the reaction at a DC voltage of 3–6 V for 0.5–5 hours (20–60 °C); and centrifuging to obtain the crude product.

[0041] Furthermore, the anode is made of any one of pure tungsten plate, tungsten-cobalt alloy, tungsten-iron alloy or tungsten-nickel alloy, preferably tungsten-cobalt alloy, and the tungsten content in the alloy is ≥70wt%.

[0042] Furthermore, the cathode can be any one of a graphite electrode, a platinum electrode, or a titanium plate, preferably a titanium plate.

[0043] Furthermore, the DC voltage can be any of 3 V, 3.5 V, 4 V, 4.5 V, 5 V, 5.5 V, or 6 V, preferably 4 V.

[0044] Furthermore, the electrolysis time can be any one of 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours, preferably 2 hours.

[0045] Furthermore, the reaction temperature range is 20–60 °C, preferably 25–35 °C, and most preferably, room temperature 25 °C.

[0046] Furthermore, the rotation speed at which the crude product is obtained by centrifugation can be any one of 5000 rpm, 6000 rpm, 7000 rpm, 8000 rpm, 9000 rpm, or 10000 rpm, preferably 8000 rpm.

[0047] Furthermore, the centrifugation time for obtaining the crude product can be any one of 15 min, 20 min, 25 min, or 30 min, preferably 20 min.

[0048] In some preferred embodiments, the washing process involves alternating washing with ethanol and deionized water 3 to 5 times.

[0049] Furthermore, the number of washes can be any one of 3, 4, or 5 times.

[0050] In some preferred embodiments, after the washing process is completed, the sample can be dried in a constant temperature oven at a temperature of 50°C, 60°C, or 70°C, preferably 60°C.

[0051] Furthermore, the drying time can be any one of 2h, 3h, 4h, 5h, or 6h, preferably 2h.

[0052] It should be noted that, unless otherwise specified, all raw materials and chemical reagents used in this invention are commercially available.

[0053] The technical solution of the present invention will be described in detail below through specific embodiments.

[0054] Example 1 This embodiment provides a tungsten oxide quantum dot, and the specific preparation method includes: Add 100 mL of deionized water to a 250 mL PTFE beaker and stir at 500 rpm on a magnetic stirrer. Simultaneously, slowly add 32.6 mL of 98% concentrated sulfuric acid dropwise at a rate of 1 mL / min to avoid localized overheating. After the mixture cools to room temperature, transfer it to a 200 mL volumetric flask and dilute to volume to obtain a 3 mol / L sulfuric acid electrolyte. Transfer this electrolyte to an electrolytic cell and maintain the electrolyte temperature at 25 ± 1 °C.

[0055] A tungsten-cobalt alloy (WC-6%Co, size 10 mm × 10 mm × 2 mm) was used as the anode, and was ultrasonically cleaned with acetone, ethanol and deionized water for 10 minutes in sequence before use; a pure titanium plate (purity 99.99%, same size) was used as the cathode, and a DC voltage of 5 V was applied for electrolysis reaction for 2 hours.

[0056] After the reaction was complete, the resulting suspension was transferred to a 50 mL centrifuge tube and centrifuged at 8000 rpm for 10 minutes to collect the precipitate. The precipitate was then washed five times alternately with deionized water and anhydrous ethanol, centrifuged under the same conditions after each wash. Finally, the product was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain yellow tungsten oxide quantum dot powder; the yield of quantum dots was 10.5 g.

[0057] See Figure 1 and Figure 2 The figures show the XRD phase diagram and TEM morphology diagram of the tungsten oxide quantum dots prepared in Example 1 of this invention. As can be seen from the figures, the prepared tungsten oxide quantum dots have good crystallinity, uniform morphology, and good dispersion of single quantum dots. The particle size of the obtained quantum dots is mainly concentrated in 2~4nm, which is smaller than the particle size of tungsten oxide quantum dots obtained by other existing technical solutions (≥10nm).

[0058] Example 2 This embodiment provides a tungsten oxide quantum dot, and the specific preparation method includes: Add 100 mL of deionized water to a 250 mL PTFE beaker and stir at 500 rpm on a magnetic stirrer. Simultaneously, slowly add 32.6 mL of 98% concentrated sulfuric acid dropwise at a rate of 1 mL / min to avoid localized overheating. After the mixture cools to room temperature, transfer it to a 200 mL volumetric flask and dilute to volume to obtain a 3 mol / L sulfuric acid electrolyte.

[0059] The sulfuric acid electrolyte was transferred to an electrolytic cell, and the electrolyte temperature was maintained at 25±1℃. A tungsten-cobalt alloy (WC-6%Co, 10 mm × 10 mm × 2 mm) was used as the anode, and was ultrasonically cleaned sequentially with acetone, ethanol, and deionized water for 10 minutes before use. A pure titanium plate (99.99% purity, same size) was used as the cathode, and a DC voltage of 6 V was applied for electrolysis for 2 hours. After the reaction, the resulting suspension was transferred to a 50 mL centrifuge tube, centrifuged at 8000 rpm for 10 minutes to collect the precipitate, and washed alternately with deionized water and anhydrous ethanol 5 times, centrifuging under the same conditions after each wash.

[0060] Finally, the product was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain yellow tungsten oxide quantum dot powder; the yield of quantum dots was 11.5g.

[0061] Example 3 This embodiment provides a tungsten oxide quantum dot, and the specific preparation method includes: Add 100 mL of deionized water to a 250 mL PTFE beaker and stir at 500 rpm on a magnetic stirrer. Simultaneously, slowly add 32.6 mL of 98% concentrated sulfuric acid dropwise at a rate of 1 mL / min to avoid localized overheating. After the mixture cools to room temperature, transfer it to a 200 mL volumetric flask and dilute to volume to obtain a 3 mol / L sulfuric acid electrolyte.

[0062] The sulfuric acid electrolyte was transferred to an electrolytic cell, and the electrolyte temperature was maintained at 25±1℃. A tungsten-cobalt alloy (WC-6%Co, size 10 mm×10 mm×2 mm) was used as the anode and was ultrasonically cleaned with acetone, ethanol and deionized water for 10 minutes in sequence before use. A pure titanium plate (purity 99.99%, size same as in Example 1) was used as the cathode, and a DC voltage of 3 V was applied for electrolysis reaction for 2 hours.

[0063] After the reaction was completed, the resulting suspension was transferred to a 50 mL centrifuge tube and centrifuged at 8000 rpm for 10 minutes to collect the precipitate. The precipitate was washed five times alternately with deionized water and anhydrous ethanol, and centrifuged under the same conditions after each wash.

[0064] Finally, the product was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain yellow tungsten oxide quantum dot powder, with a yield of ~10g.

[0065] See Figure 3 The figure shows a TEM image of the tungsten oxide quantum dots prepared in Example 3 of the present invention. As can be seen from the figure, the prepared tungsten oxide quantum dots have a uniform morphology and the particle size range is mainly concentrated in ~20nm.

[0066] Example 4 This embodiment provides a tungsten oxide quantum dot, and the specific preparation method includes: Add 100 mL of deionized water to a 250 mL PTFE beaker and stir at 500 rpm on a magnetic stirrer. Simultaneously, slowly add 32.6 mL of 98% concentrated sulfuric acid dropwise at a rate of 1 mL / min to avoid localized overheating. After the mixture cools to room temperature, transfer it to a 200 mL volumetric flask and dilute to volume to obtain a 3 mol / L sulfuric acid electrolyte.

[0067] The sulfuric acid electrolyte was transferred to an electrolytic cell, and the electrolyte temperature was maintained at 25±1℃. A tungsten-cobalt alloy (WC-6%Co, size 10 mm×10 mm×2 mm) was used as the anode and was ultrasonically cleaned with acetone, ethanol and deionized water for 10 minutes in sequence before use. A pure titanium plate (purity 99.99%, size same as in Example 1) was used as the cathode, and a DC voltage of 4 V was applied for electrolysis reaction for 2 hours.

[0068] After the reaction was completed, the resulting suspension was transferred to a 50 mL centrifuge tube and centrifuged at 8000 rpm for 10 minutes to collect the precipitate. The precipitate was washed five times alternately with deionized water and anhydrous ethanol, and centrifuged under the same conditions after each wash.

[0069] Finally, the product was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain yellow tungsten oxide quantum dot powder with a quantum dot yield of 10.5g.

[0070] The quantum dots obtained in this embodiment have similar particle size to those in Example 3, and the particle size distribution is also relatively uniform.

[0071] Example 5 This embodiment provides a tungsten oxide quantum dot, and the specific preparation method includes: Add 100 mL of deionized water to a 250 mL PTFE beaker and stir on a magnetic stirrer at 500 rpm. Simultaneously, slowly add 43.5 mL of 98% concentrated sulfuric acid dropwise at a rate of 1 mL / min to avoid localized overheating. After the mixture cools to room temperature, transfer it to a 200 mL volumetric flask and dilute to volume to obtain a 4 mol / L sulfuric acid electrolyte.

[0072] The sulfuric acid electrolyte was transferred to an electrolytic cell, and the electrolyte temperature was maintained at 25±1℃. A tungsten-cobalt alloy (WC-6%Co, 10 mm × 10 mm × 2 mm) was used as the anode, and was ultrasonically cleaned with acetone, ethanol and deionized water for 10 minutes in sequence before use. A pure titanium plate (99.99% purity, same size as in Example 1) was used as the cathode. A DC voltage of 5 V was applied, and the electrolysis reaction was carried out for 2 hours.

[0073] After the reaction was completed, the resulting suspension was transferred to a 50 mL centrifuge tube and centrifuged at 8000 rpm for 10 minutes to collect the precipitate. The precipitate was washed five times alternately with deionized water and anhydrous ethanol, and centrifuged under the same conditions after each wash.

[0074] Finally, the product was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain yellow tungsten oxide quantum dot powder with a quantum dot yield of 12.3g.

[0075] The morphology of the quantum dots in this embodiment is similar to that in Example 1, with a particle size of approximately 2-4 nm.

[0076] Example 6 This embodiment provides a tungsten oxide quantum dot, and the specific preparation method includes: Add 100 mL of deionized water to a 250 mL polytetrafluoroethylene beaker, place it on a magnetic stirrer and stir at 500 rpm, while slowly adding 43.5 mL of 98% concentrated sulfuric acid dropwise at a rate of 1 mL / min to avoid local overheating. After the mixed solution cools to room temperature, transfer it to a 200 mL volumetric flask and dilute to volume to obtain a 4 mol / L sulfuric acid electrolyte.

[0077] The sulfuric acid electrolyte was transferred to an electrolytic cell, and the electrolyte temperature was maintained at 25±1℃. A tungsten-cobalt alloy (WC-6%Co, 10 mm × 10 mm × 2 mm) was used as the anode, and was ultrasonically cleaned sequentially with acetone, ethanol, and deionized water for 10 minutes before use. A pure titanium plate (99.99% purity, same dimensions as in Example 1) was used as the cathode. A DC voltage of 6 V was applied, and the electrolysis reaction was carried out for 2 hours.

[0078] After the reaction was completed, the resulting suspension was transferred to a 50 mL centrifuge tube and centrifuged at 8000 rpm for 10 minutes to collect the precipitate. The precipitate was washed five times alternately with deionized water and anhydrous ethanol, and centrifuged under the same conditions after each wash.

[0079] Finally, the product was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain yellow tungsten oxide quantum dot powder with a quantum dot yield of 11.0 g.

[0080] The morphology of the quantum dots in this embodiment is similar to that in Embodiment 5, and will not be described again here.

[0081] Example 7 This embodiment provides a tungsten oxide quantum dot, and the specific preparation method includes: Add 100 mL of deionized water to a 250 mL PTFE beaker and stir on a magnetic stirrer at 500 rpm. Simultaneously, slowly add 43.5 mL of 98% concentrated sulfuric acid dropwise at a rate of 1 mL / min to avoid localized overheating. After the mixture cools to room temperature, transfer it to a 200 mL volumetric flask and dilute to volume to obtain a 4 mol / L sulfuric acid electrolyte.

[0082] The sulfuric acid electrolyte was transferred to an electrolytic cell, and the electrolyte temperature was maintained at 25±1℃. A tungsten-cobalt alloy (WC-6%Co, 10 mm × 10 mm × 2 mm) was used as the anode, and was ultrasonically cleaned sequentially with acetone, ethanol, and deionized water for 10 minutes before use. A pure titanium plate (99.99% purity, same dimensions as in Example 1) was used as the cathode. A DC voltage of 3 V was applied, and the electrolysis reaction was carried out for 2 hours.

[0083] After the reaction was completed, the resulting suspension was transferred to a 50 mL centrifuge tube and centrifuged at 8000 rpm for 10 minutes to collect the precipitate. The precipitate was washed five times alternately with deionized water and anhydrous ethanol, and centrifuged under the same conditions after each wash.

[0084] Finally, the product was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain yellow tungsten oxide quantum dot powder with a quantum dot yield of 10.2g.

[0085] The quantum dots obtained in this embodiment have similar particle size to those in Example 3, and the particle size distribution is also relatively uniform.

[0086] Comparative Example 1 This embodiment provides a tungsten oxide quantum dot, and the specific preparation method includes: Add 100 mL of deionized water to a 250 mL PTFE beaker and stir at 500 rpm on a magnetic stirrer. Simultaneously, slowly add 32.6 mL of 98% concentrated sulfuric acid dropwise at a rate of 1 mL / min to avoid localized overheating. After the mixture cools to room temperature, transfer it to a 200 mL volumetric flask and dilute to volume to obtain a 3 mol / L sulfuric acid electrolyte. Transfer this electrolyte to an electrolytic cell and maintain the electrolyte temperature at 25 ± 1 °C. Use a tungsten-cobalt alloy (WC-6%Co, 10 mm × 10 mm × 2 mm) as the anode, which is ultrasonically cleaned sequentially with acetone, ethanol, and deionized water for 10 minutes before use. Use a pure titanium plate (99.99% purity, same size) as the cathode. Apply a 2V DC voltage and electrolyze for 2 hours. After the reaction was complete, the resulting suspension was transferred to a 50 mL centrifuge tube and centrifuged at 8000 rpm for 10 minutes to collect the precipitate. The precipitate was then washed five times alternately with deionized water and anhydrous ethanol, centrifuged under the same conditions after each wash. Finally, the product was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain yellow tungsten oxide quantum dot powder.

[0087] Comparative Example 2 This embodiment provides a tungsten oxide quantum dot, and the specific preparation method includes: Add 100 mL of deionized water to a 250 mL PTFE beaker and stir at 500 rpm on a magnetic stirrer. Simultaneously, slowly add 32.6 mL of 98% concentrated sulfuric acid dropwise at a rate of 1 mL / min to avoid localized overheating. After the mixture cools to room temperature, transfer it to a 200 mL volumetric flask and dilute to volume to obtain a 3 mol / L sulfuric acid electrolyte. Transfer this electrolyte to an electrolytic cell and maintain the electrolyte temperature at 25 ± 1 °C. Use a tungsten-cobalt alloy (WC-6%Co, 10 mm × 10 mm × 2 mm) as the anode, which is ultrasonically cleaned sequentially with acetone, ethanol, and deionized water for 10 minutes before use. Use a pure titanium plate (99.99% purity, same size) as the cathode. Apply an 8V DC voltage and electrolyze for 2 hours. After the reaction was complete, the resulting suspension was transferred to a 50 mL centrifuge tube and centrifuged at 8000 rpm for 10 minutes to collect the precipitate. The precipitate was then washed five times alternately with deionized water and anhydrous ethanol, centrifuged under the same conditions after each wash. Finally, the product was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain yellow tungsten oxide quantum dot powder.

[0088] Results analysis: Obviously, the only difference between Example 1 and Example 3 is the voltage of the electrolysis reaction. However, by comparing the SEM images of the two, it can be seen that although the morphology of the obtained quantum dots is uniform and the particle size is almost the same, the particle size of the quantum dots in Example 3 is significantly larger than that in Example 1.

[0089] Comparing the tungsten oxide quantum dots obtained in Example 4 and Example 3, the two have similar appearances and a particle size of about 20 nm. Obviously, the quantum dots obtained under a DC voltage of 5~6V have a much smaller particle size than those obtained under a voltage of 3~4V. However, within the range of 3~6V, the quantum dots all have the characteristic of uniform size.

[0090] Compared with Example 1 and Comparative Example 2, when the electrolysis voltage is increased to 8V (greater than 6V), the particle size of the quantum dots obtained is no longer uniformly distributed, and tungsten oxide quantum dots of 5~40nm can be seen.

[0091] Compared with Example 3 and Comparative Example 1, when the electrolysis voltage is reduced to 2V (less than 3V), the particle size of the obtained quantum dots is about 2~4nm, but there is obvious agglomeration. The dispersion performance of single quantum dots is significantly reduced compared with Example 3.

[0092] Further comparison of Examples 3 and 7 shows that, under the same voltage conditions, the amount of sulfuric acid added has almost no effect on the morphology and distribution characteristics of the quantum dots within the scope of this invention.

[0093] In particular, the above method can achieve gram-level mass production of tungsten oxide quantum dots; compared with existing technologies, such as the hydrothermal method, it can achieve a single-batch yield of more than 10g.

[0094] Meanwhile, the preparation method used in this invention also has the advantages of mild conditions and green pollution. This invention can prepare quantum dots at room temperature without high temperature heating, which can significantly reduce production costs. Combined with the above-mentioned advantages of gram-level mass production, it has great value for large-scale promotion and application.

[0095] Furthermore, the present invention also tested the electrochromic properties of the tungsten oxide quantum dots prepared in the above embodiments and comparative examples, specifically including: The tungsten oxide quantum dots prepared in the above examples were ultrasonically dispersed in ethanol (molar concentration of 10 mg / mL) and uniformly deposited on an ITO conductive substrate using a spray coating method. After drying, an electrochromic electrode was obtained. Its electrochromic properties were tested in the electrolyte using a three-electrode system.

[0096] See Figure 4 The figure shows an electrochromic electrode obtained from tungsten oxide quantum dots prepared in Example 1 of this invention. As can be seen from the figure, the electrode appears blue (reduced state) under negative voltage (-0.5V) and recovers to a transparent state (oxidized state) under positive voltage (0.5V), exhibiting reversible electrochromic behavior.

[0097] Furthermore, the electrolytic reaction of the present invention can also be achieved by using pulsed voltage to prepare tungsten oxide quantum dots. Any method that can provide a stable and suitable current for the electrolytic reaction should be included within the scope of protection of the present invention.

[0098] It should be noted that the tungsten oxide quantum dots prepared by the present invention are dihydrated tungsten oxide quantum dots, which can be obtained by removing the water of crystallization. This does not affect the electrochromic properties of the tungsten oxide quantum dots prepared by the technical solution of the present invention, and the morphology of the quantum dots can be selected according to actual needs.

[0099] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments within the spirit and principles of the present invention, achieved through conventional substitutions or by realizing the same function without departing from the principles and spirit of the present invention, fall within the scope of protection of the present invention.

Claims

1. A method for preparing tungsten oxide quantum dots, characterized in that, Tungsten oxide quantum dots were prepared by electrolysis, using an acidic solution as the electrolyte and tungsten metal or a tungsten-containing alloy as the anode, under the action of voltage.

2. The method for preparing tungsten oxide quantum dots according to claim 1, characterized in that, In the electrolysis method, the electrolyte is an acidic solution; And / or, the electrolyte is hydrochloric acid or sulfuric acid; And / or, the concentration of the electrolyte is 0.01 to 5 mol / L.

3. The method for preparing tungsten oxide quantum dots according to claim 1, characterized in that, In the electrolysis reaction, the cathode is an inert electrode material; And / or, the inert electrode material is any one of titanium plate, platinum electrode or graphite electrode; preferably titanium plate.

4. The method for preparing tungsten oxide quantum dots according to claim 1, characterized in that, The tungsten-containing alloy is a tungsten-cobalt alloy or a tungsten-iron-nickel alloy.

5. The method for preparing tungsten oxide quantum dots according to claim 1, characterized in that, The voltage is either a DC voltage or a pulse voltage; And / or, the DC voltage is 3~6V; preferably 4~5V.

6. The method for preparing tungsten oxide quantum dots according to claim 1, characterized in that, The electrolysis reaction is carried out at a temperature of 20–60 °C; preferably 25 °C.

7. The method for preparing tungsten oxide quantum dots according to claim 1, characterized in that, The electrolysis reaction also includes post-processing; And / or, the post-processing includes: purifying the electrolysis product and then drying it; And / or, the purification process includes washing the electrolysis product alternately with ethanol and deionized water, centrifuging, and finally collecting the purified product; And / or, the drying process includes drying the purified product at a temperature of 50~80℃ for 2~6 hours to obtain the tungsten oxide quantum dots.

8. A tungsten oxide quantum dot, prepared by the preparation method according to any one of claims 1-7.

9. The tungsten oxide quantum dots according to claim 8, characterized in that, The quantum dot size is 2–20 nm.

10. A method for preparing tungsten oxide quantum dots as described in any one of claims 1-7, or, as described in claim 8 or 9, the application of tungsten oxide quantum dots in the fields of flexible display devices, smart windows, or photocatalysis.

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