Thin-walled hollow ZnO ball material and preparation method and application thereof

Abstract

The application belongs to the technical field of photocatalytic decomposition of water to produce hydrogen, and relates to preparation of a photocatalyst, in particular to a thin-wall hollow ZnO ball material and a preparation method and application thereof. PVP, salicylic acid and zinc acetate dihydrate are added into an organic solvent according to a mass ratio of 1:0.35-0.30:0.20-0.25, uniformly mixed, and then heated to 150-170 DEG C to perform a solvothermal reaction, and the product of the solvothermal reaction is calcined under an air atmosphere, and the thin-wall hollow ZnO ball material is obtained. The thin-wall hollow ZnO ball material can improve its specific surface area to provide more surface active sites, promote photocatalytic decomposition of water to produce hydrogen, and the hollow ball material can improve light utilization due to its wide internal space, thereby improving photocatalytic activity.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic water splitting for hydrogen production technology, and relates to the preparation of photocatalysts, specifically to a thin-walled hollow ZnO sphere material, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] ZnO, as a photocatalyst for water splitting to produce hydrogen, inherently suffers from high recombination rates of photogenerated carriers and a wide band gap. Morphology control can improve the separation and migration efficiency of photogenerated carriers. Constructing hollow ZnO materials can enhance its photocatalytic activity. However, according to the inventors' research, the current process for preparing hollow ZnO materials is complex and cumbersome, hindering cost savings and thus limiting its practical application. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a thin-walled hollow ZnO sphere material, its preparation method, and its application. The thin-walled hollow ZnO sphere material provided by the present invention can increase its specific surface area to provide more surface active sites, promote photocatalytic water splitting to produce hydrogen, and the hollow sphere material, due to its large internal space, can improve light utilization, thereby enhancing photocatalytic activity.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] In the first aspect, a method for preparing thin-walled hollow ZnO spheres involves adding polyvinylpyrrolidone (PVP), salicylic acid, and zinc acetate dihydrate to an organic solvent in a mass ratio of 1:0.35–0.30:0.20–0.25, mixing them thoroughly, and then heating the mixture to 150–170°C for a solvothermal reaction. The product of the solvothermal reaction is then calcined in an air atmosphere to obtain the final product.

[0007] This invention uses zinc acetate dihydrate as the zinc source, PVP as the template, and salicylic acid for chelation. A spherical precursor is generated through self-assembly in a solvothermal reaction, followed by calcination to obtain spherical ZnO material. During the solvothermal reaction, after zinc acetate dihydrate dissolves, its acetate anions deprotonate the carboxylic acid group of salicylic acid, and zinc ions combine with the hydroxyl groups of salicylate, thus achieving reliable coordination between the salicylic acid ligand and the metal cation, which adsorbs onto the PVP template to form the desired spherical structure. Simultaneously, calcination not only removes PVP but also utilizes the crystal faces generated on the material surface to dissolve and grow the internal grains of the precursor.

[0008] However, through experiments, this invention unexpectedly discovered that adjusting the salicylic acid content in the reaction system can regulate the morphology of the resulting ZnO. As the salicylic acid content increases, the ZnO transforms from porous solid spheres to hollow spheres. Furthermore, with a further increase in salicylic acid content, the walls of the hollow spheres gradually become thinner. The thin-walled hollow ZnO sphere material of this invention has a higher specific surface area and more active sites. Simultaneously, the hollow structure of the thin-walled hollow ZnO sphere material facilitates the reflection and refraction of light within the material, allowing more light to act on the material surface. Compared to light transmission, the reflection and refraction of light within the material improves light utilization, thereby enhancing photocatalytic activity.

[0009] Secondly, a thin-walled hollow ZnO sphere material is obtained by the above preparation method.

[0010] Thirdly, the application of the aforementioned thin-walled hollow ZnO sphere material in photocatalytic water splitting for hydrogen production.

[0011] The beneficial effects of this invention are as follows:

[0012] (1) The preparation method of the present invention can obtain thin-walled hollow ZnO spheres by simply changing the content of salicylic acid. It adopts a solvothermal method, which is simple, efficient, reproducible, has a larger specific surface area, and has more uniform size.

[0013] (2) The thin-walled ZnO material prepared by this invention has a larger specific surface area, which can provide more reactive sites, thus facilitating the adsorption and reaction of reactants. Furthermore, its spacious internal space can improve light utilization and achieve efficient photocatalytic hydrogen production. Attached Figure Description

[0014] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0015] Figure 1 This is the X-ray diffraction (XRD) pattern of the ZnO material prepared in Example 3 of this invention.

[0016] Figure 2 This is a transmission electron microscope (TEM) image of the solid porous ZnO material prepared in Example 1 of this invention, with a scale bar of 200 nm.

[0017] Figure 3 This is a transmission electron microscope (TEM) image of the thick-walled hollow ZnO material prepared in Example 2 of this invention, with a scale bar of 500 nm.

[0018] Figure 4 This is a transmission electron microscope (TEM) image of the thin-walled hollow ZnO material prepared in Example 3 of this invention, with a scale bar of 500 nm.

[0019] Figure 5 These are the photocatalytic water splitting and hydrogen production performance diagrams of ZnO materials with different morphologies prepared in Examples 1-3 of this invention. Detailed Implementation

[0020] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0021] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0022] Given the shortcomings of existing hollow ZnO materials, such as low efficiency in photocatalytic water splitting for hydrogen production, this invention proposes a thin-walled hollow ZnO sphere material, its preparation method, and its application.

[0023] A typical embodiment of the present invention provides a method for preparing thin-walled hollow ZnO spheres. Polyvinylpyrrolidone, salicylic acid, and zinc acetate dihydrate are added to an organic solvent in a mass ratio of 1:0.35-0.30:0.20-0.25, mixed evenly, and then heated to 150-170°C for a solvothermal reaction. The product of the solvothermal reaction is calcined under an air atmosphere to obtain the final product.

[0024] In some embodiments, the organic solvent is an alcohol solvent. Examples of alcohol solvents include methanol, ethanol, propanol, and isopropanol, with ethanol being preferred.

[0025] In some embodiments, PVP is first dissolved in an organic solvent, followed by the addition of salicylic acid and zinc acetate dihydrate. Adding and dissolving the template agent first helps to fully utilize the template effect of PVP and improves the success rate of preparing thin-walled hollow ZnO spheres.

[0026] In some embodiments, in the solvothermal reaction system, the volume ratio of the organic solvent to the volume of the reaction vessel is 1:1.8 to 2.2.

[0027] In some embodiments, the reaction time of the solvothermal reaction is 9 to 11 hours.

[0028] In some embodiments, the material after the solvothermal reaction is centrifuged, washed, dried, and ground, and then calcined in air. This helps to avoid the introduction of impurities that could affect the success rate of preparing thin-walled hollow ZnO spheres after calcination.

[0029] In some embodiments, the calcination temperature is 450–550°C, and the calcination time is 2–4 hours.

[0030] In some embodiments, the calcination process employs a programmed temperature rise. The programmed temperature rise rate is 0.5–1.5 °C·min. -1 .

[0031] Another embodiment of the present invention provides a thin-walled hollow ZnO sphere material, obtained by the above preparation method.

[0032] Thirdly, the application of the aforementioned thin-walled hollow ZnO sphere material in photocatalytic water splitting for hydrogen production.

[0033] Specifically, the thin-walled hollow ZnO sphere material is added to a solution and mixed evenly, and then the mixed solution is irradiated with light; wherein the solution contains a sacrificial agent.

[0034] More specifically, the sacrificial agent is sodium sulfide and sodium sulfite.

[0035] More specifically, the light source is sunlight or lamplight. Further, the lamplight is a xenon lamp.

[0036] More specifically, the ratio of the hollow ZnO sphere material to the solution is 1:8 to 10, mg:mL.

[0037] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0038] Example 1:

[0039] 1 g of PVP was dissolved in 50 mL of ethanol solution and stirred at 350 rpm for 30 min at room temperature until dissolved. Then, 0.219 g of zinc acetate dihydrate and 0.069 g of salicylic acid were added, and the mixture was magnetically stirred for 4 h at room temperature. The clear solution was transferred to a 100 mL polytetrafluoroethylene-lined reactor and solvated in an oven at 160 °C for 10 h. After natural cooling to room temperature, the resulting precipitate was centrifuged, washed, dried, and ground. The ground white powder was then subjected to heat treatment in a tube furnace at 1 °C / min. -1 The solid porous ZnO sphere material is obtained by heating to 500℃ and calcining for 3 hours, followed by natural cooling and grinding. It is denoted as ZnO-1.

[0040] Example 2:

[0041] 1 g of PVP was dissolved in 50 mL of ethanol solution and stirred at 350 rpm for 30 min at room temperature until dissolved. Then, 0.219 g of zinc acetate dihydrate and 0.138 g of salicylic acid were added, and the mixture was magnetically stirred for 4 h at room temperature. The clear solution was transferred to a 100 mL polytetrafluoroethylene-lined reactor and solvated in an oven at 160 °C for 10 h. After natural cooling to room temperature, the resulting precipitate was centrifuged, washed, dried, and ground. The ground white powder was then subjected to heat treatment in a tube furnace at 1 °C / min. -1 The material is heated to 500℃ and calcined for 3 hours. After natural cooling and grinding, a material with thick-walled hollow ZnO spheres is obtained, which is denoted as ZnO-2.

[0042] Example 3:

[0043] 1 g of PVP was dissolved in 50 mL of ethanol solution and stirred at 350 rpm for 30 min at room temperature until dissolved. Then, 0.219 g of zinc acetate dihydrate and 0.276 g of salicylic acid were added, and the mixture was magnetically stirred for 4 h at room temperature. The clear solution was transferred to a 100 mL polytetrafluoroethylene-lined reactor and solvated in an oven at 160 °C for 10 h. After natural cooling to room temperature, the resulting precipitate was centrifuged, washed, dried, and ground. The ground white powder was then subjected to heat treatment in a tube furnace at 1 °C / min. -1 The material is heated to 500℃ and calcined for 3 hours. After natural cooling and grinding, a material with thin-walled hollow ZnO spheres is obtained, which is denoted as ZnO-3.

[0044] See Figure 1 The XRD pattern of the thin-walled hollow ZnO sphere material (denoted as ZnO-3) prepared by this invention shows the characteristic peaks of wurtzite ZnO, indicating that the ZnO material was successfully prepared.

[0045] See Figure 2 The TEM image of the solid porous ZnO sphere material (denoted as ZnO-1) prepared by this invention shows that the ZnO material has a solid porous spherical morphology.

[0046] See Figure 3 The TEM image of the thick-walled hollow ZnO sphere material (denoted as ZnO-2) prepared by this invention shows that the ZnO material has a thick-walled hollow spherical morphology.

[0047] See Figure 4 The TEM image of the thin-walled hollow ZnO sphere material (denoted as ZnO-3) prepared by this invention shows that the ZnO material has a thin-walled hollow spherical morphology.

[0048] The ZnO materials with different morphologies obtained were applied to photocatalytic water splitting for hydrogen production. The experimental procedure is as follows:

[0049] 10 mg of the photocatalyst prepared in Examples 1, 2, and 3 of this invention was added to a mixed solution of sodium sulfide nonahydrate and sodium sulfite and ultrasonically dispersed. The suspension was transferred into a reactor and irradiated with a 300W xenon lamp as simulated sunlight. The amount of hydrogen generated was detected using an online gas chromatograph equipped with a thermal conductivity detector (TCD). The hydrogen production efficiency of the photocatalyst was further calculated by combining the pre-plotted standard curve.

[0050] The efficiency of the photocatalyst for water splitting to produce hydrogen prepared in this invention is shown in the figure. Figure 5 ,from Figure 5 It can be seen that the prepared ZnO material with thin-walled hollow spherical morphology has a higher photocatalytic water splitting hydrogen production efficiency than the ZnO material with thick-walled hollow spherical morphology, which in turn has a higher efficiency than the ZnO material with solid porous spherical morphology. In particular, the ZnO-3 prepared in Example 3 has a photocatalytic water splitting hydrogen production efficiency of 252.44 μmol·g. -1 ·h -1 The morphology is approximately 1.2 times that of thick-walled hollow ZnO spheres and approximately 1.42 times that of solid porous ZnO spheres. The higher the efficiency of photocatalytic hydrogen production, the thinner the wall of the prepared ZnO material. This is likely because thin-walled ZnO materials have a larger specific surface area, providing more reactive sites, which is beneficial for the adsorption and reaction of reactants. Furthermore, their spacious internal space can improve light utilization, achieving highly efficient photocatalytic hydrogen production. These results demonstrate that morphological changes are crucial for enhancing the photocatalytic activity of composite materials.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing thin-walled hollow ZnO spheres, characterized in that, Polyvinylpyrrolidone, salicylic acid, and zinc acetate dihydrate were added to an organic solvent in a mass ratio of 1:0.35~0.30:0.20~0.25, mixed thoroughly, and then heated to 150~170 °C for a solvothermal reaction. The reaction time was 9~11 h. The product of the solvothermal reaction was calcined in air to obtain the final product. The organic solvent is an alcohol solvent; the alcohol solvent is ethanol.

2. The method for preparing thin-walled hollow ZnO spheres as described in claim 1, characterized in that, First, dissolve PVP in an organic solvent, then add salicylic acid and zinc acetate dihydrate to dissolve it.

3. The method for preparing thin-walled hollow ZnO spheres as described in claim 1, characterized in that, In a solvothermal reaction system, the volume ratio of the organic solvent to the reaction vessel is 1:1.8~2.

2.

4. The method for preparing thin-walled hollow ZnO spheres as described in claim 1, characterized in that, The material after the solvothermal reaction is centrifuged, washed, dried, and ground, and then calcined in an air atmosphere.

5. The method for preparing thin-walled hollow ZnO spheres as described in claim 1, characterized in that, The calcination temperature is 450~550 ℃, and the calcination time is 2~4 h.

6. A thin-walled hollow ZnO sphere material, characterized in that, Obtained by the preparation method described in any one of claims 1 to 5.

7. The application of the thin-walled hollow ZnO sphere material as described in claim 6 in photocatalytic water splitting for hydrogen production.

8. The application as described in claim 7, characterized in that, The thin-walled hollow ZnO sphere material is added to a solution and mixed evenly, and then the mixed solution is irradiated with light; wherein, the solution contains a sacrificial agent.

9. The application as described in claim 8, characterized in that, The sacrificial agent is sodium sulfide and sodium sulfite; Alternatively, the light source is sunlight or lamplight; Alternatively, the ratio of the hollow ZnO sphere material to the solution is 1:8~10, mg:mL.

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