Erbium-doped three-dimensionally connected nanostructured tungsten oxide and method for preparing the same

Abstract

The present application relates to inorganic nano functional material and photochromic material technical field, disclose a kind of three-dimensional connected nanostructure tungsten oxide based on erbium doping and preparation method thereof, the method with tungstate as tungsten source, erbium salt as erbium source, precursor system is constructed under acidic condition, and hydrothermal reaction is carried out in the presence of promoter, obtain erbium-doped tungsten oxide nanomaterial. By adjusting acidity, hydrothermal temperature, reaction time and erbium doping amount, can make tungsten oxide gradually change from rod-like or needle-like structure into three-dimensional connected nano architecture. The obtained material has strong visible light absorption capacity and excellent photochromic performance, and can be applied to photochromic devices, ultraviolet response indicating materials, smart windows and optical information storage and other fields. The erbium-doped tungsten oxide material prepared under the preferred condition has faster color change response speed and more stable reversible color change characteristics.

Description

Technical Field

[0001] This invention relates to the field of inorganic nanomaterials and photochromic materials, specifically to a three-dimensional interconnected nanostructured tungsten oxide based on erbium doping and its preparation method. Background Technology

[0002] Tungsten oxide (WO3) is a typical inorganic photochromic material that undergoes reversible color changes under light irradiation, thus showing broad application prospects in fields such as smart windows, optical storage, sensing, and optoelectronic devices. In existing technologies, the photochromic properties of tungsten oxide are closely related to its crystal structure, morphological characteristics, particle size, defect state, and preparation process.

[0003] Currently, research on tungsten oxide modification mainly focuses on morphology control and elemental doping. A well-designed morphology can increase the specific surface area, expand light absorption paths, and improve photogenerated carrier migration; appropriate elemental doping helps to control the band structure, induce defect formation, and promote valence state transitions, thereby improving photochromic properties. However, existing WO3 materials generally suffer from slow response speed, limited visible light absorption, insufficient morphology controllability, and unimproved cycle stability. Therefore, developing an element-doped tungsten oxide nanomaterial with controllable structure, simple processing, and excellent photochromic properties is of great significance. Summary of the Invention

[0004] The present invention aims to provide an erbium-doped three-dimensional interconnected nanostructured tungsten oxide and its preparation method, in order to solve the problems of existing tungsten oxide materials in terms of photochromic response speed, visible light utilization capability and morphology controllability.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a three-dimensional interconnected nanostructured tungsten oxide based on erbium doping, with the chemical formula Er x W 1-x O3, where x is 0.005 to 0.10.

[0006] Preferably, as an improvement, x is 0.01 to 0.05.

[0007] Preferably, as an improvement, its structure is a three-dimensional interconnected structure formed by cross-linking of rod-shaped, needle-shaped, or sheet-shaped nanounits.

[0008] Preferably, as an improvement, a method for preparing erbium-doped three-dimensional interconnected nanostructured tungsten oxide includes the following steps: S1. Dissolve the tungsten source in deionized water to obtain a transparent tungsten source solution; S2. Add an acidifying agent to the tungsten source solution to form a tungsten precursor suspension; S3. Add a structure modifier to the tungsten precursor suspension and continue stirring; then add an erbium source and stir until homogeneous to obtain the reaction precursor solution. S4. Transfer the reaction precursor liquid to a closed reaction vessel for hydrothermal reaction; S5. After the reaction is complete, the mixture is allowed to cool naturally, the precipitate is separated, and after washing and drying, erbium-doped tungsten oxide three-dimensional interconnected nanostructure material is obtained.

[0009] Preferably, as an improvement, in step S1, the tungsten source is sodium tungstate.

[0010] Preferably, as an improvement, in step S2, the acidifying agent is hydrochloric acid, and the amount of hydrochloric acid added for every 0.01 mol of tungsten source is 1.0 to 2.0 mL.

[0011] Preferably, as an improvement, in step S3, the structure regulator is K2SO4 and the erbium source is ErCl3·6H2O.

[0012] Preferably, as an improvement, in step S4, the hydrothermal reaction temperature is 140–200°C and the hydrothermal reaction time is 12–36 h.

[0013] Preferably, as an improvement, in step S4, the hydrothermal reaction temperature is 150-170°C and the hydrothermal reaction time is 24 h.

[0014] Preferably, as an improvement, in step S5, the drying conditions are 50-80℃ for 4-12 hours.

[0015] The principle and advantages of this solution are as follows: In practical applications, this technical solution addresses common industry problems with existing tungsten trioxide (WO3) technologies, such as weak visible light absorption, slow photochromic response rate, poor controllability of microstructure, and insufficient stability of cyclic color change. This solution selects rare earth erbium as a dopant element. Rare earth elements possess multiple unfilled 4f electron orbitals, which can effectively control the band structure of metal oxides, induce lattice defects, and alter carrier transport behavior, thus overcoming the shortcomings of pure WO3, such as a wide band gap, response only to ultraviolet light, and difficulty in electron transitions. In terms of preparation technology, traditional WO3 often exhibits rod-like, sheet-like, or granular structures, making it difficult to simultaneously achieve high specific surface area and structural stability. This technical solution designs the preparation process from the perspective of microstructure optimization, abandoning the traditional single rod-like or needle-like tungsten oxide structure. Relying on a hydrothermal synthesis system, by controlling acidity, hydrothermal temperature, reaction time, and erbium doping amount, zero-dimensional and one-dimensional nanounits are reconstructed into a three-dimensional interconnected nanonetwork structure. This structure significantly increases the specific surface area of ​​the material, shortens the migration path of photogenerated carriers, and enhances interfacial interactions. The three-dimensional interconnected structure shortens the carrier transport distance, and erbium doping lowers the valence state transition energy barrier. Under these dual effects, the resulting material exhibits strong visible light absorption and excellent photochromic properties. At the same time, the three-dimensional network structure improves structural stability, ensuring that the color-changing performance does not decay after multiple cycles. It can be applied to photochromic devices, ultraviolet-response indicator materials, smart windows, and optical information storage.

[0016] During the technology research and development phase, achieving uniform doping of rare earth elements in the WO3 system was one of the key challenges and difficulties in developing this technical solution. Due to the difference in radius between rare earth ions and W ions, agglomeration, precipitation, or impurity phase formation can easily occur during doping, leading to a decline in material performance. This solution achieves stable introduction of rare earth elements into the WO3 lattice by optimizing the precursor ratio, reaction system acidity, hydrothermal temperature, and reaction time. Furthermore, balancing enhanced light absorption with structural stability is another technical challenge that this solution needs to address. While excessive rare earth doping may improve visible light response, it introduces too many defect centers, increasing the probability of carrier recombination. This solution controls the doping amount to enable the material to simultaneously achieve good visible light absorption, photochromic performance, and cycle stability. In this technical solution, on the one hand, rare earth doping can adjust the electronic structure of WO3, introducing an appropriate amount of defect energy levels to improve visible light absorption; on the other hand, the three-dimensional interconnected network structure can shorten the carrier migration path and improve the separation efficiency of photogenerated electrons and holes. Furthermore, the defect structure induced by rare earth elements and the three-dimensional network morphology have a synergistic effect: defects are beneficial to enhancing photoresponse, while network structure is beneficial to improving carrier utilization efficiency. The combined effect of the two makes the material exhibit photochromic performance and cycle stability that are superior to those of simple doping or simple morphology control.

[0017] In the early stages of technical solution development, the inventors attempted to use a traditional WO3 morphology system, but the improvement in visible light response was limited, and the improvement in photochromic rate was not significant. In subsequent research, increasing the rare earth doping amount resulted in excessive lattice distortion, impurity phase formation, or particle agglomeration, leading to a decline in performance. In addition, the morphologies formed under different hydrothermal temperatures, acidities, and reaction times varied considerably, and most combinations failed to simultaneously meet the requirements of enhanced light response and cycling stability. After repeated screening and optimization, the technical route of synergistic construction of rare earth doping and a three-dimensional connected network structure was finally determined, achieving simultaneous improvement in visible light absorption capacity, photochromic performance, and cycling stability. This result is not a direct derivation of existing technologies, but a technical solution obtained after extensive experimental exploration.

[0018] In summary, the beneficial effects of this technical solution are as follows: 1. This technical solution can achieve the evolution of tungsten oxide morphology from rod-shaped to three-dimensional connected structure through the coordinated control of acidity, hydrothermal temperature, reaction time and doping amount, with good structural controllability.

[0019] 2. The Er doping in this technical solution can regulate the growth behavior of WO3 crystals and improve the visible light absorption performance and band structure of the material.

[0020] 3. The doping process in this technical solution reduces the band gap of the material, making it easier for electron transitions to occur under light. 6+ / W 5+ The transformation is beneficial to improving the photochromic response speed and color change intensity.

[0021] 4. Under the optimized doping ratio of this technical solution, the material exhibits a faster photochromic response and better overall color-changing performance; the results disclosed in the paper show that Er 0.03 W 0.97 O3 has a better overall performance.

[0022] 5. This technical solution has a simple process, low equipment requirements, and good repeatability, making it suitable for further scale-up preparation. Attached Figure Description

[0023] Figure 1 These are morphological images of tungsten oxide samples obtained under different hydrochloric acid concentrations in the embodiments of the present invention.

[0024] Figure 2 These are morphological images of tungsten oxide samples obtained at different hydrothermal temperatures in the embodiments of the present invention.

[0025] Figure 3 The UV-vis absorption spectra and band gap analysis diagrams of pure WO3 and Er-doped WO3 in the embodiments of the present invention are shown.

[0026] Figure 4This is a color change diagram of the sample before and after ultraviolet irradiation and heat treatment in an embodiment of the present invention.

[0027] Figure 5 W is an embodiment of the present invention 0.97 Yb 0.03 O3XRD plot.

[0028] Figure 6 W is an embodiment of the present invention 0.97 Yb 0.03 O3 scanning electron microscope image.

[0029] Figure 7 W is an embodiment of the present invention 0.97 Yb 0.03 Color change diagram of O3 sample before and after ultraviolet irradiation and heat treatment. Detailed Implementation

[0030] The following detailed description provides further details on specific embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; and the materials and reagents used are all commercially available.

[0031] Overview of the plan: A three-dimensional interconnected nanostructured tungsten oxide based on erbium doping, with the chemical formula Er x W 1-x O3, where x is 0.005 to 0.10; erbium-doped three-dimensional interconnected nanostructured tungsten oxide is formed by cross-linking of rod-shaped, needle-shaped or sheet-shaped nanounits to form a three-dimensional interconnected structure.

[0032] A method for preparing erbium-doped three-dimensional interconnected nanostructured tungsten oxide includes the following steps: S1. Dissolve the tungsten source in deionized water to obtain a transparent tungsten source solution; the preferred tungsten source is sodium tungstate. S2. Add an acidifying agent (hydrochloric acid) to the tungsten source solution to acidify the tungsten source and form a tungsten precursor suspension; the amount of hydrochloric acid added for every 0.01 mol of tungsten source is preferably 1.0 to 2.0 mL; S3. Add the structure modifier K2SO4 to the tungsten precursor suspension and continue stirring; then add the erbium source (ErCl3·6H2O), stir and mix evenly to obtain the reaction precursor solution; S4. Transfer the reaction precursor liquid to a reaction vessel lined with polytetrafluoroethylene and carry out a hydrothermal reaction at 140-200°C for 12-36 h. S5. After the reaction is complete, allow the mixture to cool naturally, separate the precipitate, wash it with water and / or ethanol, and then dry it at 50-80℃ for 4-12 h to obtain tungsten oxide three-dimensional interconnected nanostructure material.

[0033] Example 1 The preparation method of erbium-doped tungsten oxide three-dimensional interconnected nanostructures includes the following steps: S1. Weigh 0.01 mol sodium tungstate and add it to 75 mL of deionized water. Stir magnetically until completely dissolved to obtain a transparent solution.

[0034] S2. Then slowly add 1.5 mL of concentrated hydrochloric acid, and the solution gradually turns into a yellow suspension.

[0035] S3. Add 0.15 g of potassium sulfate as a structure modifier and continue stirring for 2 h. Then add an appropriate amount of erbium chloride hexahydrate so that the molar ratio of Er to W satisfies x=0.03.

[0036] S4. The resulting mixed suspension was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel reactor and hydrothermally reacted at 160 °C for 24 h.

[0037] S5. After the reaction is complete, allow the mixture to cool naturally to room temperature. Centrifuge to collect the precipitate, wash it three times each with deionized water and ethanol, dry it at 60°C for 6 hours, and grind it to obtain erbium-doped tungsten oxide powder (Er). 0.03 W 0.97 O3).

[0038] Example 2: Effect of different amounts of hydrochloric acid (acidity) on the microstructure of tungsten oxide Based on the preparation method in Example 1, only the amount of hydrochloric acid added was adjusted: 1.5 mL, 2 mL, 2.5 mL, and 3 mL (based on 0.01 mol sodium tungstate) to obtain different doping amounts of Er. x W 1-x O3 sample. Its microstructure was characterized, and the results are as follows: Figure 1 As shown, the four sub-figures (a), (b), (c), and (d) correspond to hydrochloric acid addition amounts of 1.5 mL, 2 mL, 2.5 mL, and 3 mL, respectively, with a uniform scale bar of 200 nm.

[0039] The results show that the acidity of the system is a key parameter for regulating the morphology of tungsten oxide. The optimal acidity is 1.5 mL of hydrochloric acid (based on 0.01 mol tungsten source): at this level, the hydrolysis rate of tungstate, the nucleus generation and growth rate are best matched, and the cross-linking of nanounits can be directionally induced to form a three-dimensional interconnected structure. If the acidity is too high, it will accelerate the aggregation of nuclei and inhibit lateral growth, ultimately only generating discrete one-dimensional nanostructures.

[0040] Example 3: Sample preparation under different temperature conditions Based on the preparation method in Example 1, while keeping other conditions unchanged, the hydrothermal temperature was set to 140℃, 160℃, 180℃, and 200℃ respectively to obtain Er with different doping amounts. x W 1-x O3 sample. Its microstructure was characterized, and the results are as follows: Figure 2 As shown, the four sub-figures (a)(b)(c)(d) correspond to hydrothermal temperatures of 140℃, 160℃, 180℃, and 200℃, respectively, with a scale bar of 200 nm.

[0041] The results show that the samples obtained at 160℃ have better crystallization state and morphology, which is more conducive to the formation of a uniform structure. If the temperature is too low, crystallization is incomplete and there are more structural defects; if the temperature is too high, grain coarsening and agglomeration will occur, destroying the three-dimensional interconnected structure.

[0042] Example 4 Preparation of samples with different erbium doping levels Based on the preparation method in Example 1, only the amount of erbium chloride hexahydrate added was adjusted so that x was 0.01, 0.03, and 0.05, respectively, to obtain Er with different doping amounts. x W 1-x O3 sample. The results show that as the Er doping amount increases, the sample morphology gradually changes from rod-shaped to cross-linked interconnected structure; when x=0.03, the material exhibits excellent comprehensive optical and photochromic properties.

[0043] UV-vis absorption spectra and band gap analysis were performed on pure WO3 and Er-doped WO3. The results are as follows: Figure 3 As shown, Figure 3 The left side shows the UV-Vis absorption spectrum (wavelength 300~800 nm), characterizing the material's photoresponse range; the right side shows the calculated bandgap, with the optical bandgap (Eg) obtained by fitting using the Tauc method, and the bandgap values ​​for each component are labeled. The results show that erbium doping effectively narrows the optical bandgap of tungsten oxide, and the bandgap width gradually decreases with increasing Er doping ratio. The doping modification successfully addresses the defect of pure WO3 only responding to UV light, significantly improving visible light utilization. Although the highest doping concentration (x=0.05) results in the smallest bandgap, subsequent color-changing experiments show that x=0.03 (Er... 0.03 W 0.97 O3) is the balance point of comprehensive performance, taking into account optical absorption, structural integrity and photochromic effect.

[0044] Example 5: Photochromic Performance Test The obtained sample was irradiated under a UV light source, and the color change was observed. The results are as follows: Figure 4 As shown, the four subgraphs (a)(b)(c)(d) correspond to: pure WO3, Er, etc., respectively. 0.01 W 0.99 O3, Er 0.03W 0.97 O3, Er 0.05 W 0.95 O3. Results showed that pure WO3 gradually changed from light gray to dark blue; Er-doped samples exhibited significant bluening within a short time, with the doped samples showing color within approximately 40 seconds. The 3 mol% Er-doped sample showed a more pronounced and stable photochromic effect, indicating a synergistic effect between the band structure, lattice defects, and microscopic three-dimensional structure, achieving an optimal balance between color intensity, response rate, and reversibility. Heating enabled rapid fading of the material, demonstrating the excellent reversibility of the photochromic system and meeting the reusability requirements of applications such as smart windows and optical storage.

[0045] Example 6: Experiments on doping with different types of rare earth elements During the research and development process, in addition to Er doping, a Yb-doped WO3 system was also tested as a comparative study to examine the effects of different rare earth elements on the material structure and photochromic properties. Based on Example 1, the rare earth element was replaced with Yb, and the prepared W... 0.97 Yb 0.03 The O3 material was subjected to X-ray diffraction analysis, scanning electron microscopy analysis, and photochromic performance testing.

[0046] Research results are as follows Figure 5-7 As shown, the results indicate that Yb doping can also regulate the crystal structure and optical properties of WO3 to some extent, but its overall performance improvement effect is not as good as that of the Er-doped system. Analysis suggests that the differences in ionic radius, electronic structure, and ability to regulate lattice defects among different rare earth elements lead to varying effects on material properties.

[0047] Compared to Yb-doped systems, Er-doped systems exhibit the following characteristics: (1) It is more conducive to forming a uniform and stable three-dimensional connected network structure; (2) It has a more obvious effect on the regulation of the band structure of WO3 and a stronger ability to absorb visible light; (3) It can induce the formation of more suitable defect states and improve the separation and transport efficiency of photogenerated carriers; (4) It exhibits superior overall performance in terms of photochromic response speed, coloring depth and cycle stability.

[0048] Therefore, although Yb doping can also improve the performance of WO3 materials, Er doping can simultaneously meet the requirements of structural regulation, light absorption enhancement and cycle stability improvement, and ultimately achieve a better overall effect. Therefore, it has been identified as the preferred doping element in this technical solution.

[0049] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A three-dimensional interconnected nanostructured tungsten oxide based on erbium doping, characterized in that: The chemical formula is Er x W 1-x O3, where x is 0.005 to 0.

10.

2. The erbium-doped three-dimensional interconnected nanostructured tungsten oxide according to claim 1, characterized in that: x ranges from 0.01 to 0.

05.

3. The erbium-doped three-dimensional interconnected nanostructured tungsten oxide according to claim 2, characterized in that: Its structure is a three-dimensional interconnected structure formed by cross-linking of rod-shaped, needle-shaped, or sheet-shaped nanounits.

4. A method for preparing erbium-doped three-dimensional interconnected nanostructured tungsten oxide according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Dissolve the tungsten source in deionized water to obtain a transparent tungsten source solution; S2. Add an acidifying agent to the tungsten source solution to form a tungsten precursor suspension; S3. Add a structure modifier to the tungsten precursor suspension and continue stirring; then add an erbium source and stir until homogeneous to obtain the reaction precursor solution. S4. Transfer the reaction precursor liquid to a closed reaction vessel for hydrothermal reaction; S5. After the reaction is complete, the mixture is allowed to cool naturally, the precipitate is separated, and after washing and drying, erbium-doped tungsten oxide three-dimensional interconnected nanostructure material is obtained.

5. The method for preparing erbium-doped three-dimensional interconnected nanostructured tungsten oxide according to claim 4, characterized in that: In step S1, the tungsten source is sodium tungstate.

6. The method for preparing erbium-doped three-dimensional interconnected nanostructured tungsten oxide according to claim 5, characterized in that: In step S2, the acidifying agent is hydrochloric acid, and the amount of hydrochloric acid added is 1.0 to 2.0 mL for every 0.01 mol of tungsten source.

7. The method for preparing erbium-doped three-dimensional interconnected nanostructured tungsten oxide according to claim 6, characterized in that: In step S3, the structure regulator is K2SO4 and the erbium source is ErCl3·6H2O.

8. The method for preparing erbium-doped three-dimensional interconnected nanostructured tungsten oxide according to claim 7, characterized in that: In step S4, the hydrothermal reaction temperature is 140–200℃, and the hydrothermal reaction time is 12–36 h.

9. A method for preparing erbium-doped three-dimensional interconnected nanostructured tungsten oxide according to claim 8, characterized in that: In step S4, the hydrothermal reaction temperature is 150–170°C, and the hydrothermal reaction time is 24 h.

10. A method for preparing erbium-doped three-dimensional interconnected nanostructured tungsten oxide according to claim 9, characterized in that: In step S5, the drying conditions are 50–80℃ for 4–12 hours.

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