A WO3@ITO Heterojunction Nanocomposite and Its Preparation Method

Abstract

The present invention discloses a WO3@ITO heterojunction nanocomposite material and a preparation method thereof, belonging to the technical field of nanomaterials. The preparation method of the present invention comprises the following steps: (1) preparing WO3 nanopowders; (2) performing indium doping pretreatment on the surface of the prepared WO3 nanopowders; (3) adding the WO3 with indium doped on the surface to the precursor solution for solvothermal synthesis of ITO, enabling ITO to epitaxially grow on the surface of WO3 to obtain the WO3@ITO heterojunction nanocomposite material. The preparation method of the present invention has simple process, low cost, controllable product morphology, and the obtained composite material has good dispersibility and can be uniformly and firmly loaded on the surface of two-dimensional carriers such as carbon cloth, nickel foam, FTO, ITO, glass, etc., and can be applied in the fields of electrochromism, gas sensors, energy storage materials, photocatalysis, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and particularly to a WO3@ITO heterojunction nanocomposite material and a preparation method thereof. Background Art

[0002] Nanomaterials refer to a new generation of materials with at least one dimension in the nanoscale in three-dimensional space. Compared with macroscopic-scale materials, nanomaterials exhibit many excellent properties and have good application prospects in various fields such as mechanics, acoustics, optics, magnetism, electricity, and thermotics. Among them, metal oxide nanomaterials are widely used in the production of catalysts, gas sensors, semiconductors, and environmental remediation, etc., and are one of the most concerned types of nanomaterials currently.

[0003] Among numerous metal oxide nanomaterials, WO3 has become a research hotspot in the field of metal oxide nanomaterials due to its excellent electrochromic, gasochromic, photochromic, gas-sensing, and photocatalytic properties. WO3 is an n-type semiconductor with a band gap of about 2.5 - 3.2 eV, and can be used in fields such as gas sensors, electrochromic devices, photocatalytic water splitting for hydrogen production, photochromism, supercapacitors, and photocatalysis. However, a single WO3 thin film still has problems such as a high recombination rate of photo-generated electrons and holes, low photo-electrocatalytic activity and energy conversion efficiency, and low migration efficiency of photo-generated carriers. Therefore, researchers often improve its performance by doping or compounding WO3, etc.

[0004] Indium tin oxide (ITO) doped with tin is an n-type semiconductor material with a band gap of about 3.5 - 4.3 eV, having high electrical conductivity, high visible light transmittance, and good chemical stability, and is widely used in fields such as transparent conductive films. However, the application research on ITO nanocrystals and ITO nanocrystal composites is relatively less. In the field of electrochromics, the literature (Llordés A, Garcia G, Gazquez J, et al. Tunable near-infrared and visible-light transmittance in nanocrystal-in-glass composites[J]. Nature, 2013, 500(7462): 323 - 326.) mentions that embedding ITO nanocrystals into NbO x glass can achieve an electrochromic effect with independent regulation of visible light and near-infrared transmittance, where NbO x regulates visible light, and ITO regulates near-infrared light, achieving the effect of "dual-frequency" regulation.

[0005] In the field of electrochromics, the formation of a heterojunction by the composite of small-sized ITO nanocrystals and WO3 can, on the one hand, effectively enhance the conductivity of the WO3 thin film, making charge transfer and electrolyte penetration easier, increasing the specific surface area, and improving the electrochromic performance of WO3; on the other hand, ITO nanocrystals have certain electrochromic performance in the near-infrared region, which can be complementary to WO3 to achieve the effect of "dual-frequency" regulation of visible light and near-infrared.

[0006] To improve the electrochromic performance of WO3 and ITO, in the existing literature (Zhao Q, Fang Y, Qiao K, et al. Printing of WO3 / ITO nanocomposite electrochromic smart windows[J]. Solar Energy Materials and Solar Cells, 2019, 194: 95 - 102.), a WO3 / ITO nanocomposite was prepared by a simple physical ball milling and blending method. A heterojunction was not effectively formed between the prepared WO3 and ITO, and more of them were physically adsorbed and combined. Therefore, the electrochromic cycle stability still needs to be improved. In addition, there is also a study (Liu Y, Yuan G, Hua C, et al. Improvement of electrochromic performance by embedding ITO nanocrystals in amorphous WO3 film[J]. ECS Journal of Solid State Science and Technology, 2019, 8(1): P1.) reporting an ITO / WO3 composite electrochromic thin film with a nanocrystal embedding structure and its preparation method. The results show that the interfacial effect of the embedded ITO nanocrystals plays a key role in the electrochromic performance of the WO3 amorphous thin film, but the actual improvement effect is not significant (the optical modulation amplitude at 630 nm ranges from 42.09% of pure WO3 to 53.80% of 0.1ITO@WO3), which may be related to the too large size of ITO nanocrystals.

[0007] In fact, WO3 and ITO nanocomposites can not only be used in the field of electrochromics. Due to the excellent photocatalytic, gas-sensing characteristics and electrochemical activity of WO3 itself, this nanocomposite can also be used in fields such as photocatalysis, gas sensors, and energy storage materials. Summary of the Invention

[0008] In view of the above technical problems and the existing deficiencies in the art, the present invention aims to provide a method for preparing an in-situ synthesized WO3@ITO heterojunction nanocomposite material. On the one hand, the ITO nanocrystals in the prepared composite material have high conductivity, which can improve the conductivity of WO3; on the other hand, the composite of WO3 and ITO can form a heterojunction, which can expand the light absorption range and improve the photoelectric utilization efficiency. In addition, the WO3@ITO heterojunction nanocomposite material is easy to disperse and form a film. With the unique nanostructure, it can effectively increase the specific surface area and porosity of the composite film, thereby increasing the ion migration rate, which is beneficial to improving the response time and service life of related devices.

[0009] To solve the above existing technical problems, the method of the present invention is realized through the following technical solutions:

[0010] A WO3@ITO heterojunction nanocomposite material and a preparation method thereof, comprising the following steps:

[0011] Step S1: Obtain nano-WO3;

[0012] Step S2: Disperse the nano-WO3 prepared in Step S1 in an aqueous solution of indium acetate, stir at room temperature for 12 - 48 h. After the reaction is completed, add ethanol for centrifugal washing and drying to obtain a powder sample; then heat-treat at 350 - 400 °C for 1 - 2 h to obtain indium-doped nano-WO3; the concentration of the aqueous solution of indium acetate is 0.05 - 0.25 M; the molar ratio of nano-WO3 to indium acetate is 2:1 - 10:1;

[0013] Step S3: Add indium-doped WO3 to the precursor solution for solvent thermal synthesis of ITO for reaction. After the reaction is completed, wash out the product and disperse it in a non-polar solvent to obtain a WO3@ITO heterojunction nanocomposite material; the precursor solution for solvent thermal synthesis of ITO contains a solvent, an indium source, and a tin source. The molar ratio of indium-doped WO3, indium source, and tin source is: (2 - 50):9:1. The solvent is octadecene and oleylamine, and the volume ratio is 1:1 - 1:5. The total concentration of W, In, and Sn in the precursor solution is 0.02 - 0.2 M, the reaction temperature is 250 - 280 °C, and the reaction time is 2 - 6 h.

[0014] Further, the specific steps of Step S1 are as follows:

[0015] Prepare an aqueous solution of sodium tungstate dihydrate with a pH of 2.0 and a concentration of 0.1 - 0.15 M, and then add ammonium sulfate. After mixing evenly, obtain a WO3 precursor solution; react the WO3 precursor solution at 150 - 200 °C for 6 - 24 h. After the reaction product is centrifugally washed and dried with deionized water and ethanol, nano-WO3 is obtained; the molar ratio of sodium tungstate dihydrate to ammonium sulfate is 1:1 - 1:5.

[0016] Further, in step S3, the indium source is one or more of indium acetate and indium acetylacetonate.

[0017] According to the preparation method, it is characterized in that in step S3, the tin source is one or more of stannous acetate, stannous octoate, and dimethyl di-neodecanoate stannous.

[0018] Further, the non-polar solvent in step S3 is selected from one or more of the following substances: toluene, tetrachloroethylene, chloroform, isopentane, n-pentane, cyclopentane, petroleum ether, n-hexane, cyclohexane, isooctane, n-heptane, and trimethylpentane.

[0019] A WO3@ITO heterojunction nanocomposite material is prepared by using the preparation method described above.

[0020] The application of the WO3@ITO heterojunction nanocomposite material as an electrochromic material, a gas sensor, an energy storage material, and a photocatalytic material.

[0021] Due to the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention first prepares nano-WO3 by hydrothermal or solvothermal means, then obtains WO3 with an In2O3 seed layer through surface indium doping modification treatment, and finally in-situ grows ITO nanocrystals on the surface of WO3 by solvothermal method to obtain a WO3@ITO heterojunction nanocomposite material. This composite material has good dispersibility and is easy to form a film, and can be uniformly and firmly loaded on the surface of two-dimensional carriers such as carbon cloth, nickel foam, FTO, ITO, glass, etc., and can be used in the fields of electrochromics, gas sensors, energy storage materials, and photocatalysis.

[0023] 2. For the WO3@ITO heterojunction nanocomposite material prepared by the present invention, on the one hand, it can effectively enhance the conductivity of the WO3 thin film, make charge transfer and electrolyte penetration easier, and can effectively enhance the electrochromic performance of WO3.

[0024] 3. For the WO3@ITO heterojunction nanocomposite material prepared by the present invention, on the other hand, the ITO nanocrystals have certain electrochromic performance due to local surface plasmon resonance in the near-infrared region, which can be complementary to WO3, and can achieve the electrochromic effect of "dual-frequency" regulation in the visible light and near-infrared regions. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0026] Figure 1 Schematic diagram of the preparation process for Example 1

[0027] Figure 2 HRTEM image of WO3 nanorods prepared by the hydrothermal method in Example 1

[0028] Figure 3 Low-magnification TEM image of WO3@ITO heterojunction nanocomposites prepared in Example 1

[0029] Figure 4 HRTEM image of WO3@ITO heterojunction nanocomposites prepared in Example 1

[0030] Figure 5 HRTEM image of WO3-ITO nanomaterials prepared in Comparative Example 1

[0031] Figure 6 EDS spectrum of Example 1

[0032] Figure 7 Electrochromic spectral modulation performance of the WO3@ITO heterojunction nanocomposites prepared in Example 1 after spin-coating into a film Detailed implementation manners

[0033] In the present invention, nano-WO3 is first prepared by the hydrothermal method, and then an In2O3 seed layer is formed on the surface of WO3 through indium doping treatment on the surface, which helps the nucleation and growth of ITO nanocrystals. Finally, WO3@ITO heterojunction composites are prepared through a solvothermal reaction. The formed heterojunction can accelerate the carrier migration rate and improve the performance and stability of the material. To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. The experimental methods without specific conditions noted in the following embodiments are usually in accordance with conventional conditions or the conditions recommended by the manufacturer.

[0034] Example 1:

[0035] A preparation method of WO3@ITO heterojunction nanocomposites, as Figure 1 shown, includes the following steps:

[0036] Step S1: Prepare nano-WO3;

[0037] Add 0.825 g of sodium tungstate dihydrate to 19 mL of deionized water. After stirring for 30 min, adjust the pH of the solution to 2.0 with 3 M hydrochloric acid. Subsequently, add 0.66 g of ammonium sulfate and stir for 1 h to prepare the WO3 precursor solution. Pour the precursor solution into a 50 mL reaction kettle liner, tighten it, and place it in an oven for reaction at 180 °C for 12 h. After the reaction product is centrifugally washed and dried with deionized water and ethanol, nano-WO3 is obtained.

[0038] Step S2: Perform indium doping pretreatment on the surface of the prepared nano-WO3.

[0039] Disperse 100 mg of the nano-WO3 prepared in S1 in 10 mL of an aqueous solution of indium acetate (0.1 M), stir at room temperature for 24 h. After stirring, add ethanol for centrifugal washing to obtain a precipitate, and then dry it overnight in a blast drying oven at 60 °C to obtain a powder sample. Finally, heat this powder in a corundum boat in a muffle furnace to 350 °C and perform heat treatment for 2 h to obtain indium-doped nano-WO3 on the surface.

[0040] Step S3: Add the indium-doped WO3 to the precursor solution for solvothermal synthesis of ITO for reaction; First, add 10 mL of octadecene to a 100 mL three-necked flask, and then add 100 mg of the surface-modified WO3 nano powder obtained in Step S2, stir for 30 min, then add 0.108 mmol of indium acetate, 0.012 mmol of stannous 2-ethylhexanoate, and 3.2 mL of oleylamine. Before heating, turn on the magnetic stirrer and introduce high-purity nitrogen for 30 min to remove the residual air in the flask. Subsequently, start heating and gradually raise the temperature to 270 °C within 30 min and maintain it for 2 h. Remove the heating jacket, cool to room temperature, centrifuge with ethanol, wash out the product, and disperse it in n-hexane to prepare the WO3@ITO heterojunction nanocomposite.

[0041] Comparative Example 1:

[0042] Step S1: Prepare nano-WO3;

[0043] Add 0.825 g of sodium tungstate dihydrate to 19 mL of deionized water. After stirring for 30 min, adjust the pH of the solution to 2.0 with 3 M hydrochloric acid. Subsequently, add 0.66 g of ammonium sulfate and stir for 1 h to prepare the WO3 precursor solution. Pour the precursor solution into a 50 mL reaction kettle liner, tighten it, and place it in an oven for reaction at 180 °C for 12 h. After the reaction product is centrifugally washed and dried with deionized water and ethanol, nano-WO3 is obtained.

[0044] Step S2: Directly add the WO3 nanorods to the precursor solution for solvothermal synthesis of ITO for reaction;

[0045] First, add 10 mL of octadecene to a 100 mL three-necked flask, and then add 100 mg of the WO3 nanorods prepared in step S1. Stir for 30 min, then add 0.108 mmol of indium acetate, 0.012 mmol of stannous 2-ethylhexanoate, and 3.2 mL of oleylamine. Before heating, turn on the magnetic stirrer and introduce high-purity nitrogen for 30 min to remove the residual air in the flask. Subsequently, start heating and gradually increase the temperature to 270 °C within 30 min and maintain for 2 h. Remove the heating jacket, cool to room temperature, centrifuge with ethanol, wash out the product, and disperse it in n-hexane to obtain the WO3-ITO nanomaterial.

[0046] Figure 2 It is the HRTEM image of the WO3 nanorods prepared by the hydrothermal method in Example 1. It can be seen that the h-WO3 nanorods prepared by the hydrothermal method grow along the

[0002] crystal plane.

[0047] Figure 3 It is the low-magnification TEM image of the WO3@ITO heterojunction nanocomposite prepared in Example 1. It can be clearly seen that most of the ITO nanocrystals nucleate and grow heterogeneously on the surface of WO3, forming the WO3@ITO heterojunction.

[0048] Figure 4 It is the HRTEM image of the WO3@ITO heterojunction nanocomposite prepared in Example 1. It can be clearly seen that the WO3 nanorods prepared by hydrothermal synthesis are wrapped by a shell composed of ITO nanocrystals.

[0049] Figure 5 It is the HRTEM image of the WO3-ITO nanomaterial prepared in Comparative Example 1. It can be seen that part of the ITO is combined with WO3 to form a heterojunction, but the epitaxial growth effect is not as good as that of WO3 modified and pretreated in Example 1. It shows that the pretreatment of the present invention makes a seed layer of In2O3 grow on the surface of WO3, and subsequent in-situ nucleation and growth are easy, so that a better WO3@ITO heterojunction can be formed.

[0050] Figure 6 It is the EDS spectrum of Example 1. It can be seen that there is a layer of ITO nanocrystals wrapped outside the WO3 nanorods, which verifies that the obtained is the WO3@ITO heterojunction nanocomposite.

[0051] Figure 7 It is the electrochromic spectral modulation performance of the WO3@ITO heterojunction nanocomposite prepared in Example 1 after spin-coating into a film. It can be seen that the prepared film has a large optical modulation amplitude in the visible light and near-infrared regions.

[0052] Example 2:

[0053] A preparation method of a WO3@ITO heterojunction nanocomposite, as Figure 1As shown in the figure, it includes the following steps:

[0054] Step S1: Prepare nano WO3;

[0055] Add 0.825 g of sodium tungstate dihydrate to 19 mL of deionized water. After stirring for 30 min, adjust the pH of the solution to 2.0 with 3 M hydrochloric acid. Then add 0.33 g of ammonium sulfate and stir for 1 h to obtain a WO3 precursor solution. Pour the precursor solution into a 50 mL reactor liner, tighten it, and place it in an oven at 150 °C for 24 h. After the reaction product is centrifugally washed and dried with deionized water and ethanol, nano WO3 is obtained;

[0056] Step S2: Perform indium doping pretreatment on the surface of the prepared nano WO3;

[0057] Disperse the nano WO3 prepared in S1 in 10 mL (0.1 M) aqueous solution of indium acetate and stir at room temperature for 12 h. After stirring, add ethanol for centrifugal washing to obtain a precipitate. Then dry it overnight in a blast drying oven at 60 °C to obtain a powder sample. Finally, heat this powder in a corundum boat in a muffle furnace to 400 °C and heat-treat it for 1 h to grow a seed layer of In2O3 on the surface of WO3, which is conducive to in-situ nucleation and growth subsequently.

[0058] Step S3: Add indium-doped WO3 to the precursor solution for solvothermal synthesis of ITO and react; First, add 10 mL of octadecene to a 100 mL three-necked flask, then add 100 mg of surface-modified WO3 nano powder obtained in Step S2 and stir for 30 min. Then add 0.108 mmol of indium acetate, 0.012 mmol of stannous 2-ethylhexanoate, and 2 mL of oleylamine. Before heating, turn on the magnetic stirrer and introduce high-purity nitrogen for 30 min to remove the residual air in the flask. Then start heating and gradually raise the temperature to 250 °C within 30 min and keep it for 6 h. Remove the heating jacket, cool to room temperature, centrifuge with ethanol, wash out the product, and disperse it in n-hexane to obtain a WO3@ITO heterojunction nanocomposite.

[0059] Example 3:

[0060] A preparation method of a WO3@ITO heterojunction nanocomposite, as Figure 1 shown, includes the following steps:

[0061] Step S1: Prepare nano WO3;

[0062] Add 0.825 g of sodium tungstate dihydrate to 25 mL of deionized water. After stirring for 30 min, adjust the pH of the solution to 2.0 with 3 M hydrochloric acid. Subsequently, add 1.65 g of ammonium sulfate and stir for 1 h to obtain a WO3 precursor solution. Pour the precursor solution into a 50 mL reaction kettle liner, tighten it, and place it in an oven for reaction at 200 °C for 6 h. After the reaction product is centrifugally washed and dried with deionized water and ethanol, nano-WO3 is obtained.

[0063] Step S2: Perform indium doping pretreatment on the surface of the prepared nano-WO3.

[0064] Disperse 100 mg of the nano-WO3 prepared in S1 in 10 mL (0.25 M) of an aqueous solution of indium acetate and stir at room temperature for 12 h. After stirring, add ethanol for centrifugal washing to obtain a precipitate, and then dry it overnight in a blast drying oven at 60 °C to obtain a powder sample. Finally, heat this powder to 350 °C in a corundum boat in a muffle furnace for heat treatment for 2 h to grow a seed layer of In2O3 on the surface of WO3, which is conducive to in-situ nucleation and growth subsequently.

[0065] Step S3: Add indium-doped WO3 to the precursor solution for solvothermal synthesis of ITO for reaction; First, add 10 mL of octadecene to a 100 mL three-necked flask, and then add 150 mg of the surface-modified WO3 nano powder obtained in Step S2 and stir for 30 min. Then add 0.108 mmol of indium acetate, 0.012 mmol of stannous 2-ethylhexanoate, and 3.2 mL of oleylamine. Before heating, turn on the magnetic stirrer and introduce high-purity nitrogen for 30 min to remove the residual air in the flask. Subsequently, start heating and gradually raise the temperature to 280 °C within 30 min and maintain it for 3 h. Remove the heating jacket, cool to room temperature, centrifuge with ethanol, wash out the product, and disperse it in n-hexane to obtain a WO3@ITO heterojunction nanocomposite.

[0066] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Without conflict, the embodiments of the present application and the features in the embodiments can be arbitrarily combined with each other.

Claims

1. A preparation method of WO3@ITO heterojunction nanocomposite, characterized in that, It includes the following steps: Step S1: Prepare nano WO3; Step S2: Disperse the nano WO3 prepared in Step S1 in an aqueous solution of indium acetate, stir at room temperature for 12 - 48 h. After the reaction is completed, add ethanol for centrifugal washing and drying to obtain a powder sample; then heat-treat at 350 - 400 °C for 1 - 2 h to obtain indium-doped nano WO3; the concentration of the aqueous solution of indium acetate is 0.05 - 0.25 M; the molar ratio of nano WO3 to indium acetate is 2:1 - 10:1; Step S3: In a 100 mL three-necked flask, add the indium-doped nano WO3 prepared in S2 to the precursor solution for solvothermal synthesis of ITO for reaction. After the reaction is completed, wash out the product and disperse it in a non-polar solvent to obtain a WO3@ITO heterojunction nanocomposite material; the precursor solution for solvothermal synthesis of ITO contains a solvent, an indium source, and a tin source. The molar ratio of the indium-doped nano WO3, indium source, and tin source synthesized in S2 is (2 - 50):9:

1. The solvent is octadecene and oleylamine, and the volume ratio is 1:1 - 5:

1. The total concentration of W, In, and Sn in the precursor solution is 0.02 - 0.2 M. The reaction temperature is 250 - 280 °C, and the reaction time is 2 - 6 h; the indium source is one or more of indium acetate or indium acetylacetonate.

2. The preparation method according to claim 1, characterized in that, The specific content of Step S1 is as follows: Prepare an aqueous solution of sodium tungstate dihydrate with a pH of 2.0 and a concentration of 0.1 - 0.15 M, and then add ammonium sulfate. After mixing evenly, obtain a WO3 precursor solution; react the WO3 precursor solution at 150 - 200 °C for 6 - 24 h. After the reaction product is centrifugally washed and dried with deionized water and ethanol, nano WO3 is obtained; the molar ratio of sodium tungstate dihydrate to ammonium sulfate is 1:1 - 1:

5.

3. The preparation method according to claim 1, characterized in that, In Step S3, the tin source is one or more of tin acetate, stannous octoate, or dimethyldineodecanoate tin.

4. The preparation method according to claim 1, characterized in that, In Step S3, the non-polar solvent is selected from one or more of the following substances: toluene, tetrachloroethylene, chloroform, isopentane, n-pentane, cyclopentane, petroleum ether, n-hexane, cyclohexane, isooctane, n-heptane, trimethylpentane.

5. A WO3@ITO heterojunction nanocomposite, characterized in that, It is prepared by using the preparation method described in any one of claims 1 - 4.

6. Application of the WO3@ITO heterojunction nanocomposite material according to claim 5 as an electrochromic material, gas sensor, energy storage material, and photocatalytic material.

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