Preparation method of WO3 hollow sphere heterojunction and application of WO3 hollow sphere heterojunction in ultraviolet detector

Abstract

The invention discloses a preparation method of a WO3 hollow sphere, an egg-shaped WO3-TiO2 heterojunction and a sea urchin-shaped WO3-ZnO heterojunction, and an application of the WO3 hollow sphere, the egg-shaped WO3-TiO2 heterojunction and the sea urchin-shaped WO3-ZnO heterojunction in an ultraviolet detector. The WO3 hollow sphere disclosed by the invention is composed of a large number of nano-particles and shows rough surface characteristics and a hollow spherical nano-structure with a hollow interior; the'egg '-shaped WO3-TiO2 heterojunction shows that a layer of thin TiO2 shell layer wraps the outer part of the WO3 hollow sphere, and the whole body is in an'egg'-shaped form; the'sea urchin '-shaped WO3-ZnO heterojunction takes a WO3 hollow sphere as a core, ZnO nanorods are densely and approximately vertically grown on the surface of the sphere, and the whole'sea urchin'-shaped microstructure is presented. The preparation method comprises the following steps: synthesizing a WO3 hollow sphere by adopting a hydrothermal method, further respectively preparing an egg-shaped WO3-TiO2 heterojunction composite material and a sea urchin-shaped WO3-ZnO heterojunction composite material through solution synthesis, and constructing an ultraviolet detector by taking the obtained material as a detection material, and the detector can detect ultraviolet light without additionally applying bias voltage. The WO3 hollow sphere, the egg-shaped WO3-TiO2 heterojunction with a unique microstructure and the sea urchin-shaped WO3-ZnO heterojunction with a unique microstructure are synthesized by utilizing a simple solution method, the ultraviolet detector with a self-energy-supply characteristic is further prepared, and the ultraviolet detector is suitable for the field of photoelectric detection. The preparation process is easy to operate, low in cost, free of environmental pollution and suitable for large-scale production, and has wide application prospects and remarkable practical value.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor photoelectric detectors and their fabrication technology, specifically relating to ultraviolet detectors of WO3 hollow spheres, "egg"-shaped WO3-TiO2 heterojunctions and "sea urchin"-shaped WO3-ZnO heterojunctions and their fabrication methods. Background Technology

[0002] In recent years, ultraviolet (UV) detectors have been widely used in defense, military, and civilian fields such as missile early warning, optical communication, and environmental monitoring. However, traditional UV detectors are large in size and require an external power supply, significantly increasing manufacturing and maintenance costs, which to some extent restricts their practical application. Therefore, developing a semiconductor-based self-powered UV detector that can achieve rapid response and detection of UV light without an external bias voltage, and is simple in structure and low in cost, has become a current research hotspot. Among many semiconductors, WO3, as a wide-bandgap (2.8 eV) semiconductor metal oxide, is considered a promising UV light detection material due to its high electron mobility, good chemical and thermal stability. However, the rapid recombination of photogenerated carriers in WO3 material severely weakens its UV detector performance. Furthermore, the low specific surface area of ​​bulk WO3 limits its UV light absorption efficiency, restricting its application in the field of UV detection. To address these issues, coupling suitable semiconductor materials with WO3 to construct heterojunctions with unique nanostructures is considered an effective strategy for developing high-performance WO3-based self-powered UV detectors. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing WO3 hollow spheres, as well as egg-shaped WO3-TiO2 heterojunctions and sea urchin-shaped WO3-ZnO heterojunctions, and their applications in ultraviolet detectors.

[0004] This invention uses a hydrothermal method to prepare WO3 hollow spheres, and further obtains "egg-shaped" WO3-TiO2 heterojunctions and "sea urchin-shaped" WO3-ZnO heterojunctions through a solution method. Working electrodes are constructed using WO3 hollow spheres, "egg-shaped" WO3-TiO2 heterojunctions, and "sea urchin-shaped" WO3-ZnO heterostructures, respectively. After being connected to the counter electrode through a heat-sealing film, electrolyte is injected into the device cavity to obtain an ultraviolet detector with good self-powering characteristics, which can be further applied in the field of ultraviolet detection.

[0005] The objective of this invention is to be achieved through the following technical solutions:

[0006] A method for preparing the above-mentioned WO3 hollow spheres, the method comprising the following steps:

[0007] Step 1: Mix 0.5–1.5 mol / L glucose solution and 0.015–0.05 mol / L sodium tungstate dihydrate solution in equal proportions. Then, transfer the mixture to a high-temperature reactor and place it in a constant-temperature drying oven at 180–250°C for 8–36 hours. After the reaction, wash the mixture 3–5 times sequentially with deionized water and anhydrous ethanol, and dry it at room temperature to 60°C to obtain WO3 powder.

[0008] Step 2: Anneal the WO3 powder obtained in Step 1 at 350-450℃ for 20-120 minutes to obtain WO3 hollow spheres.

[0009] The aforementioned WO3 hollow spheres exhibit a clear hollow nanosphere structure, composed of a large number of tightly packed nanoparticles, resulting in a rough and uneven surface.

[0010] A method for preparing an "egg-shaped" WO3-TiO2 heterojunction, the method comprising the following steps:

[0011] Step 1: Preparation of WO3 hollow spheres. The WO3 powder obtained in Step 1 is added to a mixed solution containing 0.01–0.1 mol / L ammonium fluorotitanate and 0.1–0.2 mol / L boric acid, and reacted at room temperature for 3–9 hours. After the reaction, the WO3 is washed 3–5 times by centrifugation with deionized water and anhydrous ethanol, and then dried at room temperature to 60°C to obtain WO3-TiO2 material.

[0012] Step 2: The WO3-TiO2 material obtained in Step 1 is annealed at 350-450℃ for 20-120 minutes to obtain an "egg"-shaped WO3-TiO2 heterojunction.

[0013] The aforementioned "egg"-shaped WO3-TiO2 heterojunction is characterized by a thin TiO2 shell separately wrapping around the outside of the WO3 hollow sphere core, together forming a unique "egg"-shaped heterojunction structure.

[0014] A method for preparing a "sea urchin"-shaped WO3-ZnO heterojunction, the method comprising the following steps:

[0015] Step 1: Prepare an anhydrous ethanol solution containing 0.005–0.01 mol / L sodium hydroxide and 0.005–0.01 mol / L zinc acetate dihydrate, and incubate at 60°C for 1–3 hours. Then allow it to stand at room temperature for 6–18 hours to obtain the seed solution.

[0016] Step 2: Add the WO3 powder synthesized in Step 1 to 5-10 mL of seed solution, mix thoroughly, and stir at room temperature for 20-60 minutes.

[0017] Step 3: Transfer the solution obtained in Step 2 to 50–100 mL of a solution containing 0.07–0.12 mol / L zinc nitrate hexahydrate and 0.02–0.05 mol / L hexamethylenetetramine. Mix thoroughly and react in a water bath at 80–100 °C for 4–9 hours. After the reaction is complete, wash the solution 3–5 times by centrifugation with deionized water and anhydrous ethanol, and then dry it at room temperature to 60 °C to obtain WO3-ZnO material.

[0018] Step 4: Anneal the WO3-ZnO material obtained in Step 3 at 350-450℃ for 20-120 minutes to obtain a "sea urchin" shaped WO3-ZnO heterojunction.

[0019] A method for fabricating a WO3-based self-powered ultraviolet detector, the method comprising the following steps:

[0020] Hollow WO3 spheres were uniformly dispersed in an appropriate amount of deionized water, then drop-coated onto the surface of a conductive substrate. After drying, the working electrode of the ultraviolet detector was obtained. The working electrode and the counter electrode were sealed together by a heat-sealing film, creating an internal cavity. Electrolyte was then injected into the cavity using a vacuum reflux method, thus producing the ultraviolet detector.

[0021] Furthermore, the material of the working electrode in this invention can be one of an "egg"-shaped WO3-TiO2 heterojunction and a "sea urchin"-shaped WO3-ZnO heterojunction.

[0022] Furthermore, the conductive substrate in this invention is one of ITO and FTO glass.

[0023] Furthermore, the counter electrode in this invention is one of Pt electrode, ITO, and FTO glass.

[0024] Furthermore, the electrolyte in this invention is one of iodine electrolyte and polysulfide electrolyte.

[0025] Beneficial effects

[0026] The advantages of this invention compared to existing technologies are as follows: The successfully synthesized WO3 hollow sphere structure can form a closed optical path, allowing light to undergo multiple reflections on the inner wall of the shell, effectively preventing direct light penetration or absorption and reflection only on the surface, thereby significantly improving the material's light absorption capacity. Furthermore, an innovative "egg-shaped" WO3-TiO2 heterojunction with a multi-shell hollow sphere structure was constructed. This strategy, while promoting carrier separation through the formation of a type II band structure, also exhibits a multi-level cavity structure and ordered shell arrangement in morphology, effectively confining incident light within the multi-shell cavity and enhancing the material's light scattering and absorption. In addition, by controlling the surface morphology of the multi-shell hollow spheres, a "sea urchin"-shaped WO3-ZnO heterojunction hollow sphere structure with densely arranged nanorods on the surface was successfully obtained. This structure optimizes incident light capture while improving electron transport efficiency. Finally, an ultraviolet detector with excellent self-powered characteristics was prepared using the above materials as the ultraviolet light detection material. Its process is simple, suitable for large-scale production, and has high application value. Attached Figure Description

[0027] Figure 1 SEM image of a WO3 hollow sphere;

[0028] Figure 2 SEM image of an egg-shaped WO3-TiO2 heterostructure;

[0029] Figure 3 SEM image of a WO3-ZnO heterostructure resembling a sea urchin;

[0030] Figure 4 The photocurrent curve of the WO3 hollow sphere ultraviolet detector;

[0031] Figure 5 Photocurrent curve of an egg-shaped WO3-TiO2 heterojunction ultraviolet detector;

[0032] Figure 6 The photocurrent curve of the WO3-ZnO heterojunction ultraviolet detector with a "sea urchin" shape. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to the embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0034] Example 1:

[0035] This embodiment provides a method for preparing WO3 hollow spheres, the steps of which are as follows:

[0036] Step 1: Mix 18 mL of 1.25 mol / L glucose solution with 18 mL of 0.04 mol / L sodium tungstate dihydrate solution. Then, transfer the prepared solution precursor to a high-temperature reactor and keep it at 210°C for 20 hours. After the reaction is complete, wash the solution five times with deionized water and anhydrous ethanol, and dry it at room temperature to obtain WO3 powder.

[0037] Step 2: Anneal the obtained WO3 powder at 450℃ for 60 minutes to obtain WO3 hollow spheres.

[0038] Figure 1 SEM images of the WO3 hollow spheres are shown, clearly revealing that these nanostructures exhibit a typical spherical morphology with an average diameter of approximately 350 nm. Their surfaces are composed of a large number of tightly packed nanoparticles, exhibiting a rough and uneven texture. Furthermore, a distinct cavity is observed within the spherical structure through the broken structure, indicating the successful construction of the hollow sphere structure.

[0039] Figure 1 SEM images of the WO3 hollow spheres are shown, clearly revealing that these nanostructures exhibit a typical spherical morphology with an average diameter of approximately 350 nm. Their surfaces are composed of a large number of tightly packed nanoparticles, exhibiting a rough and uneven texture. Furthermore, a distinct cavity is observed within the spherical structure through the broken structure, indicating the successful construction of the hollow sphere structure.

[0040] Example 2:

[0041] This embodiment provides a method for preparing an "egg-shaped" WO3-TiO2 heterojunction, the steps of which are as follows:

[0042] Step 1: 0.1 g of the WO3 powder synthesized in Step 1 of Example 1 was added to a mixed solution containing 0.05 mol / L ammonium fluorotitanate and 0.15 mol / L boric acid, and the mixture was stirred at room temperature for 6 hours. After the reaction was completed, the mixture was washed 5 times each with deionized water and anhydrous ethanol by centrifugation, and then dried at room temperature to obtain the WO3-TiO2 material.

[0043] Step 2: The WO3-TiO2 material obtained in Step 1 is annealed at 450℃ for 60 minutes to obtain an "egg"-shaped WO3-TiO2 heterojunction.

[0044] SEM image of an egg-shaped WO3-TiO2 heterostructure as shown below Figure 2As shown in the figure. The results show that the "egg"-shaped WO3-TiO2 heterojunction still maintains a spherical shape. The outer layer is a TiO2 shell composed of fine particles. From the damaged area in the figure, it can be observed that there is an obvious cavity structure inside, and there is a hollow WO3 sphere. The two are separated from each other, and the whole structure shows an "egg" shape similar to an "egg shell" enclosing an "egg yolk".

[0045] Example 3:

[0046] This embodiment provides a method for preparing a "sea urchin"-shaped WO3-ZnO heterojunction, the steps of which are as follows:

[0047] Step 1: Prepare an anhydrous ethanol solution containing 0.006 mol / L sodium hydroxide and 0.007 mol / L zinc acetate dihydrate, and incubate at 60°C for 3 hours. Then let it stand at room temperature for 8 hours to obtain the seed solution.

[0048] Step 2: Add 0.1g of the WO3 powder synthesized in Step 1 of Example 1 to 5mL of seed solution, mix thoroughly, and stir at room temperature for 25 minutes.

[0049] Step 3: Transfer the solution obtained in Step 2 to 70 mL of a solution containing 0.09 mol / L zinc nitrate hexahydrate and 0.03 mol / L hexamethylenetetramine. Mix thoroughly and react in a water bath at 80°C for 8 hours. After the reaction is complete, wash the solution five times by centrifugation with deionized water and anhydrous ethanol, and then dry it at room temperature to obtain WO3-ZnO material.

[0050] Step 4: Anneal the WO3-ZnO material obtained in Step 3 at 450℃ for 60 minutes to obtain a "sea urchin" shaped WO3-ZnO heterojunction.

[0051] The microstructure of the "sea urchin"-shaped WO3-ZnO heterojunction was characterized by SEM. For example... Figure 3 As shown, the outer surface of this heterojunction is covered with vertical and dense ZnO nanorods, giving it a unique "sea urchin" appearance. Observation of the damaged shell clearly reveals a hollow WO3 sphere within the cavity of the shell.

[0052] Example 4:

[0053] This embodiment provides a method for fabricating a WO3 hollow sphere ultraviolet detector, as detailed below:

[0054] Step 1: Disperse the WO3 hollow spheres synthesized in Example 1 uniformly in 2 mL of deionized water, then drop-coat them onto an FTO substrate, and allow them to dry naturally to form a working electrode.

[0055] Step 2: Using blank FTO glass as the counter electrode, the working electrode and the FTO counter electrode are hot-pressed at 150°C for 15 seconds, and then connected through a heat-sealing film. Finally, polysulfide electrolyte is injected into the device to complete the fabrication of the WO3 hollow sphere ultraviolet detector.

[0056] Under conditions without an applied voltage, the fabricated WO3 hollow sphere ultraviolet detector was connected to a Keithley 2400 digital source meter, and its ultraviolet detection performance was tested using a 365nm wavelength light source as simulated ultraviolet light. Figure 4 As shown, when irradiated with ultraviolet light, the photocurrent of the device rapidly increases to 0.38 μA and remains stable; however, after the ultraviolet light is turned off, the photocurrent quickly returns to its initial state, which fully demonstrates the high sensitivity of the device to ultraviolet light. After five test cycles, the photocurrent of the WO3 hollow sphere ultraviolet detector shows a consistent trend, and the maximum photocurrent value remains stable with almost no attenuation. This indicates that the fabricated WO3 hollow sphere ultraviolet detector has the characteristics of fast response speed and good stability, and can operate without an external bias voltage.

[0057] Example 5:

[0058] This embodiment provides a method for fabricating an "egg-shaped" WO3-TiO2 heterojunction ultraviolet detector, the specific steps of which are as follows:

[0059] Using the egg-shaped WO3-TiO2 heterojunction prepared in Example 2 as the detection material, and following the device fabrication process described in Example 4, an egg-shaped WO3-TiO2 heterojunction ultraviolet detector was successfully fabricated. Under no bias voltage, the performance of the detector was evaluated using a Keithley 2400 digital source meter with 365nm ultraviolet light as the light source. Figure 5 As shown, when the ultraviolet light source is turned on, the photocurrent of the device rapidly increases to 3.7 μA. After the ultraviolet light source is turned off, the device current quickly returns to its initial state. The egg-shaped WO3-TiO2 heterojunction ultraviolet detector fabricated above showed no significant attenuation of photocurrent after 5 test cycles, exhibiting excellent stability and self-powering characteristics.

[0060] Example 6:

[0061] This embodiment provides a method for fabricating a "sea urchin"-shaped WO3-ZnO heterojunction ultraviolet detector, as detailed below:

[0062] Using the "sea urchin"-shaped WO3-ZnO heterojunction prepared in Example 3 as the detection material, an ultraviolet detector with the "sea urchin"-shaped WO3-ZnO heterojunction was fabricated under the same conditions according to the device fabrication process in Example 4. Its ultraviolet detection performance test results are as follows: Figure 6 As shown, under no incident light illumination, the device current remains in a quiescent state close to 0 microamps; however, under ultraviolet light illumination, the photocurrent rapidly increases to 5.87 microamps and remains constant. After the ultraviolet light is turned off, the device current quickly returns to the quiescent state. After five repeated switching tests, the device still exhibits almost consistent photocurrent response, which fully demonstrates that the detector has a fast response capability and stable detection performance to ultraviolet light. In addition, the testing process of the "sea urchin"-shaped WO3-ZnO heterojunction ultraviolet detector was carried out under zero bias voltage, exhibiting satisfactory self-powering characteristics.

[0063] The above description of the present invention is only a preferred embodiment of the present invention and is not intended to limit the implementation of the present invention. Those skilled in the art can easily make corresponding modifications or alterations based on the main concept and spirit of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection claimed in the claims.

Claims

1. A WO3 hollow ball, characterized in that: The surface of the sphere is tightly composed of a large number of nanoparticles, showing a rough and uneven feature. There is an obvious cavity structure inside, and the overall shape is a hollow nanosphere.

2. A method for preparing WO3 hollow spheres as claimed in claim 1, characterized in that: The method comprises the following steps: Step 1: Evenly mix 0.5-1.5 mol / L glucose solution and 0.015-0.05 mol / L sodium tungstate dihydrate solution in equal proportions, then transfer the mixed solution to a high-temperature reaction kettle, place it in a constant temperature drying oven, and react at 180-250°C for 8-36 hours. After the reaction is completed, centrifuge and wash with deionized water and anhydrous ethanol for 3-5 times in sequence, and dry it at room temperature to 60°C to obtain WO3 powder; Step 2: annealing the WO3 powder at 350-450°C for 20-120 minutes to obtain WO3 hollow spheres.

3. An "egg" shaped WO3-TiO2 heterojunction, characterized in that: A thin TiO2 shell wraps around the outside of the WO3 hollow sphere, and the WO3 hollow sphere and the TiO2 shell together form an "egg"-shaped heterojunction.

4. A method for preparing the "egg" shaped WO3-TiO2 heterojunction according to claim 3, characterized in that: The method comprises the following steps: Step 1, adding the WO3 powder obtained in step 1 of claim 2 to a mixed solution of 0.01-0.1 mol / L ammonium fluorotitanate and 0.1-0.2 mol / L boric acid, reacting at room temperature for 3-9 hours, then centrifugally washing with deionized water and anhydrous ethanol for 3-5 times, and then drying at room temperature to 60°C to obtain a WO3-TiO2 material; Step 2: anneal the WO3-TiO2 material obtained in step 1 at 350-450°C for 20-120 minutes to obtain an "egg" shaped WO3-TiO2 heterojunction.

5. A "sea urchin" shaped WO3-ZnO heterojunction, characterized in that: The core of the WO3 hollow sphere is wrapped by a dense and nearly vertically grown ZnO nanorod shell, forming the unique "sea urchin" appearance of the WO3-ZnO heterojunction.

6. A method for preparing the "sea urchin" WO3-ZnO heterojunction according to claim 5, characterized in that: The method comprises the following steps: Step 1, prepare an anhydrous ethanol solution of 0.005-0.01 mol / L sodium hydroxide and 0.005-0.01 mol / L zinc acetate dihydrate, keep warm at 60° C. for 1-3 hours, and then stand at room temperature for 6-18 hours to obtain a seed solution; Step 2: Add the WO3 powder synthesized in step 1 of claim 2 to 5-10 mL of seed solution, mix thoroughly, and react at room temperature for 20-60 minutes; Step 3, transferring the solution obtained in step 2 to 50-100 mL of a solution containing 0.05-0.12 mol / L zinc nitrate hexahydrate and 0.02-0.05 mol / L hexamethylenetetramine, mixing evenly, reacting in a water bath at 80-100° C. for 4-9 hours, and after the reaction, centrifugally washing with deionized water and anhydrous ethanol for 3-5 times in sequence, and then drying at room temperature to 60° C. to obtain a WO3-ZnO material; Step 4: anneal the WO3-ZnO material obtained in step 3 at a temperature of 350-450° C. for 20-120 minutes to obtain a "sea urchin"-shaped WO3-ZnO heterojunction.

7. A WO3-based self-powered ultraviolet detector, characterized in that: WO3 hollow spheres are evenly dispersed in deionized water and then drop-coated on the surface of a conductive substrate. After drying, a working electrode of the UV detector is formed. The working electrode is sealed and connected to the counter electrode by a heat-sealing film, a cavity is constructed inside, and iodine electrolyte or polysulfide electrolyte is injected into the cavity by a vacuum reflux method to obtain a WO3 hollow sphere self-powered UV detector.

8. A WO3-based self-powered ultraviolet detector according to claim 7, characterized in that: The material for constructing the working electrode can be one of an "egg" shaped WO3-TiO2 heterojunction and a "sea urchin" shaped WO3-ZnO heterojunction.

9. A WO3-based self-powered ultraviolet detector according to claim 7, characterized in that: The conductive substrate is one of ITO and FTO glass; the counter electrode is one of Pt electrode, ITO and FTO glass.

10. A WO3-based self-powered ultraviolet detector according to claim 7, characterized in that: The heat sealing temperature is 100-180°C.

Images