Preparation method of In2O3 hollow spheres

Abstract

The invention discloses a preparation method of In2O3 micron-sized hollow spheres, which comprises the following steps: (1) dissolving indium nitrate and urea in ethanol, then putting the solution in a hydrothermal kettle, carrying out hydrothermal reaction at 180 + / -20 DEG C for 10 + / -2 hours, centrifuging and washing the product, and drying; (2) annealing the product at the temperature of 400 + / -30 DEG C for 1.5 + / -0.5 hours to obtain an In2O3 micron-sized hollow sphere; the molar ratio of indium nitrate to urea is 1: 10 + / -3. The indium nitrate, the urea and the ethanol are analytically pure grades, and the indium nitrate is a pure phase or hydrate. Therefore, the In2O3 micron-sized hollow sphere is obtained, and a better effect can be achieved when the In2O3 micron-sized hollow sphere is used for photocatalysis.

Description

Technical Field

[0001] The invention relates to a method for preparing In2O3 micron-sized hollow spheres. The In2O3 micron-sized hollow spheres prepared in this way can be used in the field of photocatalysis, such as photochemical reduction of carbon dioxide, and belong to the field of new material technology. Background Art

[0002] Reducing and utilizing carbon dioxide produced by human activities is an effective means to mitigate the greenhouse effect. In the research of carbon dioxide conversion, hydrogenation to synthesize alkane / hydrocarbon fuels is a hot topic and is expected to be widely industrialized. The light-assisted reverse water gas reaction (PRGWS) can effectively convert CO2 into fuel and is considered to be a promising strategy to cope with the greenhouse effect and store solar energy.

[0003] Indium oxide is an important metal oxide semiconductor with a suitable band gap for photochemical reactions. However, the traditional process used to make indium oxide produces a small specific surface area, which leads to a limited number of exposed active sites. This limitation hinders the material's potential for application in photochemical reactions.

[0004] Constructing a finer microstructure is considered to be an effective way to increase the specific surface area, among which constructing a hollow structure is a common means. There are usually template methods and non-template methods. Template method, that is, before synthesis, a material is needed as a template, the required material is grown on the template, and then the template is removed by calcination and other methods to obtain the required hollow material. For example, Beijing University of Chemical Technology uses pollen as a template to prepare hollow indium tin oxide (CN113060757A). This method has a complicated actual operation process, and the final hollow material may be contaminated by the template material, so the non-template method has been greatly developed, such as using the Kirkendall effect to prepare hollow microstructures. The research group of the present invention has reported a method for preparing binary metal oxide hollow spheres using metal nitrates and organic acids as raw materials (patent number CN106517311B), specifically, the raw materials are dissolved in water in a certain proportion, and a precursor precipitate is obtained by hydrothermal treatment. The precursor precipitate is dried after centrifugation and washing, and finally the precursor is burned to obtain multi-shell hollow nanospheres. Jinan University has proposed a simple method for preparing hollow indium oxide spheres (CN102060320B), using pure indium nitrate, ethanol, and triblock polymer P123 as reaction raw materials, and obtaining indium oxide through solvent heat and washing. However, the cost of pure indium nitrate and triblock polymer P123 in this method is relatively high, which is not suitable for mass production. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing In2O3 micron hollow spheres, which prepares oxide In2O3 micron hollow spheres without using a template; the purpose of the present invention is also to provide a use of In2O3 micron hollow spheres, that is, In2O3 micron hollow spheres are used for photochemical reactions. Since In2O3 micron hollow spheres can limit the reflection of incident photons, thereby enhancing the absorption of light, and because they have a large surface area, In2O3 micron hollow spheres are good photocatalytic materials. Using them for photochemical reduction of carbon dioxide can achieve good results.

[0006] The technical solution of the present invention is: a method for preparing In2O3 micron-sized hollow spheres, comprising the following steps:

[0007] (1) Indium nitrate and urea are dissolved in ethanol, and then the solution is placed in a hydrothermal reactor for hydrothermal reaction at 180±20°C for 10±2 hours. The product is centrifuged, washed, and then dried; (2) The above product is annealed at 400±30°C for 1.5±0.5 hours to obtain In2O3 micron-sized hollow spheres. The weight of ethanol is more than 20 times that of urea;

[0008] The molar ratio of indium nitrate to urea is 1:10±3. Indium nitrate can be pure indium nitrate or indium nitrate hydrate. The presence of a small amount of crystal water will not have a significant effect on the product, but indium nitrate that has been significantly deliquesced will have a significant effect on the structure, shape and composition of the product.

[0009] The obtained In2O3 micron-sized hollow spheres are composed of nanospheres with a size of 10-20 nanometers, and the In2O3 micron-sized hollow spheres are polycrystalline.

[0010] Dissolve indium nitrate and urea in deionized water and stir magnetically for more than 30 minutes until the solution is clear and transparent to ensure uniform dispersion.

[0011] The reaction time is about 10 hours at a temperature of about 180°C.

[0012] After the product is separated by centrifugation, it is washed with water, ethanol and acetone respectively.

[0013] The product is dried in an oven at a temperature of 60° C. for 8 to 24 hours, or freeze-dried.

[0014] The hydrothermal product was annealed at 400° C. for 1.5 hours in a muffle furnace to obtain In2O3 micron-sized hollow spheres, which can achieve good photocatalytic effects.

[0015] The method of the present invention uses an ethanol-soluble metal nitrate, indium nitrate, which is added to ethanol and ten times the molar amount of urea is added. After solvent thermal treatment, a precursor precipitate is obtained, which is washed and dried and annealed at an appropriate temperature to obtain In2O3 micron-sized hollow spheres. This method only requires one solvent thermal step, while the template method often requires multiple hydrothermal steps. The key to this method is to use a metal salt and urea that are soluble in ethanol at the same time. This method may be applied to more water-soluble metal salts and urea to synthesize multi-metal oxides. The principle of the amount of citric acid used is: the molar ratio of metal ions to urea in the metal salt is 1:10.

[0016] The beneficial effects of the present invention are as follows: indium nitrate metal soluble salt and urea are added to an ethanol solvent at the same time, and a precursor is obtained through a solvent thermal step, and the steps are simple and convenient. Among them, the raw material urea is cheap, stable and non-toxic. At the same time, after the precursor is annealed, In2O3 micron-sized hollow spheres with a special structure are obtained, and this structure is very beneficial to photocatalysis, and the catalytic effect is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is an X-ray diffraction (XRD) spectrum of the In2O3 micron-sized hollow spheres according to an embodiment of the present invention.

[0018] Figure 2 (a) and (b) are scanning electron microscope (SEM) images of In2O3 micron-sized hollow spheres of different magnifications according to an embodiment of the present invention.

[0019] Figure 3 It is a transmission electron microscope (TEM) picture of the In2O3 micron-sized hollow spheres according to an embodiment of the present invention. Figure 3 (a) shows the contrast between the edge and the center of the sphere, (b) shows that the In2O3 micron-sized hollow sphere is composed of nanospheres with a size of more than ten nanometers, and (c) indicates that the In2O3 micron-sized hollow sphere is polycrystalline.

[0020] Figure 4 It is the ultraviolet-visible light absorption spectrum of the In2O3 micron-sized hollow spheres according to the embodiment of the present invention.

[0021] Figure 5 1 is a nitrogen adsorption curve of the In2O3 micron-sized hollow sphere according to an embodiment of the present invention.

[0022] Figure 6 It is the activity of the light-assisted reverse water gas reaction of the In2O3 micron-sized hollow spheres of the embodiment of the present invention. DETAILED DESCRIPTION

[0023] (1) 1.00 g of indium nitrate hydrate and 3.00 g of urea were added to 150 ml of ethanol, and magnetic stirring was performed for more than 30 min to obtain a colorless transparent solution; the molar ratio of the metal ion of the metal salt to the urea was 1:10;

[0024] (2) Pour the colorless transparent solution into a 200 ml polytetrafluoroethylene-lined stainless steel autoclave, heat to 180°C, react for 10 hours, and cool with the furnace after the reaction is complete;

[0025] (3) centrifuging the reaction product to obtain a solid powder, washing it with deionized water, ethanol and acetone in sequence, and then drying it at 60° C. for 8 to 24 hours to obtain a precursor;

[0026] (4) The precursor is annealed in a muffle furnace at 400° C. for 1.5 h to obtain In2O3 micron-sized hollow spheres. Thus, the In2O3 micron-sized hollow spheres are obtained, which can achieve good photocatalytic effects.

[0027] The product was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible absorption spectroscopy and nitrogen adsorption.

[0028] Figure 1 This is the XRD diagram of the In2O3 micron-sized hollow sphere of the embodiment of the present invention. The embodiment of the present invention is marked as V-In2O3, and the indium oxide produced by Aladdin was directly purchased and marked as C-In2O3. By comparison, the main peak positions of the crystal planes (222), (400), (440) and (622) are all aligned. By comparing the standard card of cubic phase indium oxide, the main peak positions can also be aligned.

[0029] Figure 2 (a) and (b) are scanning electron microscope (SEM) images of In2O3 micron-sized hollow spheres of the embodiment of the present invention at different magnifications. From the broken spheres, it can be seen that the spheres shown are hollow structures. Figure 2 (b) A partial enlarged view.

[0030] Figure 3 : is a transmission electron microscope (TEM) image of the In2O3 micron-sized hollow sphere of the embodiment of the present invention, wherein Figure 3 (a) The difference in contrast between the edge and center of the sphere shows that the sphere is a hollow structure. Figure 3 (b) shows that the In2O3 micron-sized hollow spheres are composed of nanospheres with a size of more than ten nanometers. Figure 3 (c) shows that In2O3 micron-sized hollow spheres are polycrystalline.

[0031] Figure 4This is the ultraviolet-visible absorption spectrum of the In2O3 micron-sized hollow spheres of the embodiment of the present invention. After fitting the figure, it is obtained that the band gap of the product V-In2O3 is 2.15 eV, while the band gap of C-In2O3 is 2.64 eV.

[0032] Figure 5 This is the nitrogen adsorption curve of the In2O3 micron-sized hollow sphere of the embodiment of the present invention. The specific surface area is calculated to be 107.49 m 2 g -1 In contrast, the specific surface area of ​​C-In2O3 is 30.36 m 2 g -1 .

[0033] The photochemical reverse water gas reaction was carried out using the In2O3 micron-sized hollow sphere photocatalyst prepared in the embodiment, specifically as follows: first, 5 mg of the photocatalyst was weighed and placed in a closed jar. The volume of the entire reaction system was 170 ml, and the light source was a 300 W xenon lamp; then the reaction system was evacuated, and high-purity CO2 gas and H2 gas were introduced, with a partial pressure of 50 kPa each, so that the pressure in the reaction system was standard atmospheric pressure. After several hours of dark light adsorption, the light was turned on for irradiation, and about 3 ml of gas was taken out from the system at intervals of 1 h and injected into a gas chromatograph to analyze the amount of CO produced.

[0034] The relationship between the amount of CO and time is as follows: Figure 5 The results show that In2O3 micron-sized hollow spheres have significant photocatalytic activity for CO2 reduction.

[0035] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for preparing In2O3 micron-sized hollow spheres, characterized in that: The following steps are involved: (1) Dissolving indium nitrate and urea in ethanol, and then placing the solution in a hydrothermal reactor for hydrothermal reaction at 180±20°C for 10±2 hours, and drying the product after centrifugation and washing; (2) Annealing the product at 400±30°C for 1.5±0.5 hours to obtain In2O3 micron-sized hollow spheres; the molar ratio of indium nitrate to urea is 1:10±3.

2. The method for preparing In2O3 micron-sized hollow spheres according to claim 1, characterized in that: The indium nitrate, urea and ethanol are all of analytical grade, wherein the indium nitrate is in pure phase or hydrate.

3. The method for preparing In2O3 micron-sized hollow spheres according to claim 1 or 2, characterized in that: The In2O3 micron-sized hollow spheres are composed of nanospheres with a size of 10-20 nanometers, and the In2O3 micron-sized hollow spheres are polycrystalline.

4. The method for preparing In2O3 micron-sized hollow spheres according to claim 1, 2 or 3, characterized in that: The weight of ethanol is more than 20 times that of urea.

5. The method for preparing In2O3 micron-sized hollow spheres according to claim 1, 2 or 3, characterized in that: The reaction time is 10 h at a temperature of about 180°C.

6. The method for preparing In2O3 micron-sized hollow spheres according to claim 1, 2 or 3, characterized in that: After the product is separated by centrifugation, it is washed with water, ethanol and acetone respectively.

7. The method for preparing In2O3 micron-sized hollow spheres according to claim 1, 2 or 3, characterized in that: The product is dried in an oven at a temperature of 60° C. for 8 to 24 hours, or freeze-dried.

8. The method for preparing In2O3 micron-sized hollow spheres according to any one of claims 1 to 7, characterized in that: The solvent thermal product was annealed in a muffle furnace at 400° C. for 1.5 hours to obtain In2O3 micron-sized hollow spheres.

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