Preparation method and application of ZnO nanoplate photocatalyst with special morphology

Abstract

The present invention discloses a method for manufacturing a ZnO nanoplate photocatalyst with a special morphology, which comprises the following steps: S1. Preparation of a NaOH solution: Weigh 4 g of sodium hydroxide and dissolve it in 50 mL of deionized water; S2. Add 1 g - 6.6 g of Zn(CH3COO)2·2H2O to the NaOH solution obtained in step S1, and magnetically stir to dissolve to obtain a uniformly mixed white turbid solution; S3. Fill the turbid solution obtained in step S2 to about 85% of the volume of the polytetrafluoroethylene inner liner of the reaction kettle, seal the reaction kettle, put it into an oven, react at 140 °C for 24 h, take out the reaction kettle, cool it to room temperature, centrifuge and wash the precipitate with absolute ethanol and deionized water respectively, and dry it at 60 °C for 12 h. Finally, collect the sample to obtain the ZnO nanoplate photocatalyst.

Description

Technical Field

[0001] The present application relates to the technical field of photocatalysts, and in particular to a preparation method and application of a ZnO nanoplate photocatalyst with a special morphology. Background Art

[0002] Photocatalytic technology is one of the effective ways to solve environmental pollution problems. Metal oxide ZnO is widely used as a photocatalytic material in photocatalytic technology due to its strong oxidizing properties, non-toxicity, good band gap energy, and excellent chemical stability. ZnO can degrade organic matter through its own redox reaction without producing secondary pollution, but its band gap is large, the electron and hole recombination speed is fast, the photon yield is small, and its nanomaterials are easy to agglomerate and reduce its specific surface area, which affects the widespread use of photocatalyst nano ZnO. Summary of the invention

[0003] 1. Technical issues

[0004] He Xinhao et al. prepared a complex morphology flake self-assembled ZnO by precipitation conversion-calcination method. The degradation rate of methylene blue by this catalyst can reach more than 94% within 8 hours (He Xinhao, Li Yuhu, Chen Jinlong, Yu Shikai, Zhang Zhongtang. Jiangxi Metallurgy, 2022, 42(06):7-14.); Du Yonghui et al. synthesized rod-shaped, flake-shaped and flower-shaped ZnO by direct precipitation method and found that flake ZnO had the highest photocatalytic efficiency for rhodamine, while rod-shaped ZnO had the lowest catalytic efficiency (Du Yonghui, Li Yuhuan, Yang Tongxiao, Sun Si Jin, Chen Hong. Journal of Jilin University (Science Edition), 2022, 60(06): 1452-1458.); Zhang Jin et al. synthesized micro-nano rod-shaped ZnO by liquid phase reaction control, and within 3 hours, its degradation rate of methylene blue reached 77% (Zhang Jin, Xiang Yuntian, Zhang Yuze, Zhang Xinran, Huo Di. Chemical New Materials, 2022, 50(S1): 191-195. DOI: 10.19817 / j.cnki.issn1006-3536.2022.S.034.). As mentioned above, the morphology of photocatalyst ZnO has a great influence on its catalytic performance, because its synthesis conditions and synthesis methods will affect the morphology of nanomaterials. At present, although the morphology of nanostructured ZnO has been reported, the preparation method and photocatalytic performance of ZnO nanoplates with special morphology are relatively few.

[0005] Technical Solution

[0006] On one hand, the present invention provides a ZnO nanoplate photocatalyst with a special morphology. The catalyst is synthesized by combining a precipitation method with a hydrothermal method, using zinc acetate and NaOH as raw materials and adjusting their mass ratio. The specific operation is as follows:

[0007] S1. Preparation of NaOH solution: weigh 4 g of sodium hydroxide (NaOH) and dissolve it in 50 mL of deionized water;

[0008] S2. Add different masses of Zn(CH3COO)2·2H2O (1 g-6.6 g) to the NaOH solution obtained in step S1, and dissolve by magnetic stirring to obtain a uniformly mixed white turbid solution.

[0009] S3. Fill the turbid liquid obtained in step S2 to about 85% of the volume of the polytetrafluoroethylene liner of the reactor, seal the reactor, put it in an oven, react at 140°C for 24 hours, take out the reactor, cool it to room temperature, centrifuge and wash the precipitate with anhydrous ethanol and deionized water respectively, and dry it at 60°C for 12 hours. Finally, collect the sample to obtain the ZnO nanoplate photocatalyst.

[0010] Furthermore, nano ZnO has different morphologies with different masses of Zn(CH3COO)2·2H2O (1g-6.6g). When the zinc salt is 1g, the synthesized ZnO is a nanorod. As the zinc salt increases to 2g, the morphology of the prepared ZnO is mainly composed of nanoneedles aggregated and grown to form a sea urchin shape; however, as the mass of zinc salt increases to 6.6g, the morphology of ZnO is mainly composed of nanoplates with a thickness of 160nm, with plates perpendicular to it on its surface, which gives it a larger specific surface area, increases the number of its catalytic active sites, and helps to improve its photocatalytic activity.

[0011] On the other hand, the present invention can use the synthesized special morphology ZnO nanoplate as a photocatalyst in photocatalytic technology. The ZnO nanoplate is a 160nm nanoplate with a plate perpendicular to it on its surface, has a large specific surface area, and has good catalytic performance.

[0012] (III) Beneficial effects

[0013] The present invention aims at the fact that the morphology of different nano ZnO has a great influence on its photocatalytic activity. In this paper, the mass ratio of zinc salt and NaOH is adjusted to form a precipitate, and the precipitate is then treated by a hydrothermal method to prepare a ZnO nanoplate with a special morphology. The special structure can increase the specific surface area of ​​the photocatalyst, increase the photocatalytic active sites, and is beneficial to improving its ability to photocatalytically degrade pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 : SEM images of ZnO synthesized under the conditions of zinc salt with a mass of 1g (a), 2g (b) and 6.6g (c);

[0015] Figure 2 : XRD patterns of ZnO synthesized under the conditions of 1g (a), 2g (b) and 6.6g (c) of zinc salt;

[0016] Figure 3 : UV-vis graphs and catalytic efficiency graphs of ZnO adsorption and degradation of methyl orange prepared under different mass ratios of zinc salt to NaOH. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] See also Figure 1-3 As shown, the present invention provides a method for preparing a special morphology ZnO nanoplate photocatalyst. First, weigh 4g of sodium hydroxide (NaOH) and dissolve it in 50mL of deionized water. Add 1g, 2g and 6.6g of Zn(CH3COO)2·2H2O to the NaOH solution, respectively. Dissolve it by magnetic stirring to obtain a uniformly mixed white turbid solution. Fill the obtained turbid solution to about 85% of the volume of a polytetrafluoroethylene reactor. Seal the reactor, put it in an oven and heat it to 140°C and keep it warm for 24 hours. Take out the reactor, cool it to room temperature, centrifuge and wash its precipitate, and dry it at 60°C for 12 hours. The synthesized ZnO has the following morphology: Figure 1 As shown in the figure, as the mass ratio of zinc salt to NaOH increases, the morphology of the product changes accordingly; when the zinc salt is less, the synthesized ZnO is a nanorod, and as the zinc salt increases to 2g, the morphology of the prepared ZnO is mainly a sea urchin shape formed by the aggregation and growth of nanoneedles; however, as the mass of zinc salt increases to 6.6g, the morphology of ZnO is mainly a nanoplate with a thickness of 160nm, and there are plates perpendicular to it on its surface, which gives it a larger specific surface area, increases the number of its catalytic active sites, and helps to improve its photocatalytic activity.

[0019] also, Figure 2 Figure 3 is the XRD diagram of the synthesized ZnO. The diffraction peak positions of each sample are consistent with the standard spectrum of ZnO (JCPDS36-145). The diffraction crystal planes of the three strongest characteristic diffraction peaks are (100), (002) and (101) crystal planes from left to right, and the corresponding 2θ angles are 32.0°, 34.6° and 36.5°, respectively, indicating that the synthesized ZnO crystal structure is a hexagonal wurtzite structure. The diffraction peaks of each crystal plane are strong and sharp, without any impurity peaks, proving that the sample purity and crystallinity of the obtained nano ZnO product are very high.

[0020] The synthesized ZnO nanoplates were used as photocatalysts to measure the photocatalytic activity of the samples. 100 mg of catalytic material was added to two beakers containing 50 mg / L methyl orange solution. One group was subjected to dark adsorption reaction, and the other group was subjected to catalytic reaction under ultraviolet light (175 WHg). Magnetic stirring was maintained during the reaction process. After 120 min, 10 mL of methyl orange solution was taken respectively, and the upper clear liquid was taken after high-speed centrifugation. The absorbance was measured using a UV-visible photometer (λmax = 464 nm). The catalytic efficiency (η) of the catalyst was calculated according to formula (1):

[0021] η=(A 吸附 -A 紫外 ) / A O (1)

[0022] Where A0, Aabsorption, and Aultraviolet represent the absorbance of 50 mg / L methyl orange solution, dark adsorption reaction, and the absorbance of methyl orange solution after 120 min of ultraviolet light (175 WHg) catalytic reaction, respectively. Figure 3 As shown, the absorbance of the dark adsorption reaction of the synthesized ZnO is not much different from the absorbance of the original solution, indicating that the adsorption effect of the nano ZnO sample is very weak. Under ultraviolet photocatalytic conditions, the absorbance of the methyl orange solution decreases significantly. Among them, when the special morphology ZnO nanoplate is used as a catalyst, the absorbance of methyl orange decreases significantly in the same time, which shows that the catalyst has a significant effect on the degradation of methyl orange. Its catalytic efficiency is 97%, which is 55% higher than that of the first two morphologies of ZnO, indicating that the special morphology is conducive to improving the photocatalytic activity of ZnO.

[0023] It should be noted that, in this article, terms such as "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0024] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a ZnO nanoplate photocatalyst with a special morphology, characterized in that: The steps include: S1. Preparation of NaOH solution: weigh 4 g of sodium hydroxide and dissolve it in 50 mL of deionized water; S2. To the NaOH solution obtained in step S1, 6.6 g of Zn(CH3COO)2·2H2O was added and dissolved by magnetic stirring to obtain a uniformly mixed white turbid solution; S3. Fill the turbid liquid obtained in step S2 to about 85% of the volume of the polytetrafluoroethylene liner of the reactor, seal the reactor, put it in an oven, react at 140°C for 24 hours, take out the reactor, cool it to room temperature, centrifuge and wash the precipitate with anhydrous ethanol and deionized water respectively, and dry it at 60°C for 12 hours. Finally, collect the sample to obtain the ZnO nanoplate photocatalyst.

2. The method for producing a special morphology ZnO nanoplate photocatalyst according to claim 1, characterized in that: When 6.6 g of Zn(CH3COO)2·2H2O was added, the morphology of ZnO was mainly nanoplates with a thickness of 160 nm, and the surface of the nanoplates had plates perpendicular to it.

3. Application of ZnO nanoplates with special morphology prepared by the method of claim 1, characterized in that: It is used in photocatalytic technology. The ZnO nanoplate is a 160nm nanoplate with a plate perpendicular to it on its surface, and has a large specific surface area.

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