MnWO4 / ZnIn2S4 heterojunction photocatalyst as well as preparation method and application thereof

Abstract

The invention relates to a MnWO4 / ZnIn2S4 heterojunction photocatalyst as well as a preparation method and application thereof, and belongs to the technical field of photocatalytic materials. In the experiment process, MnWO4 is dissolved in a precursor solution of ZnIn2S4, the MnWO4 / ZnIn2S4 heterojunction composite materials with different molar ratios are obtained by changing the molar ratio of an Mn source, and the MnWO4 / ZnIn2S4 heterojunction composite materials can be applied to the field of hydrogen evolution through photocatalytic water decomposition. Compared with an existing photocatalyst, the MnWO4 / ZnIn2S4 heterojunction has the advantages that the controllability is good when the MnWO4 / ZnIn2S4 heterojunction serves as a catalyst, the separation efficiency of current carriers can be further improved, and it is obtained through experiments that the composite material has high hydrogen yield and good stability when being used for photocatalytic water splitting. The method is green and environment-friendly, simple, convenient to operate and low in material preparation cost, conforms to the green and environment-friendly concept advocated at present, and has a wide application market prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and particularly relates to a MnWO4 / ZnIn2S4 heterojunction photocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, the development of efficient and green hydrogen resources has become the focus of attention of most researchers. As an environmentally friendly, sustainable, and renewable energy source, hydrogen is becoming increasingly popular because it has the potential to alleviate the energy shortage caused by the abuse of fossil fuels. So far, many methods for producing hydrogen energy have been established, including high-temperature decomposition of water and electrolytic catalytic water splitting. In particular, photocatalytic water splitting for hydrogen production is easy to operate and widely applicable, and is a potential environmental protection technology. However, it is not easy to achieve high hydrogen production. Therefore, a key issue in high-performance photocatalytic water splitting for hydrogen evolution is to explore photocatalysts that can effectively achieve charge separation.

[0003] ZnIn2S4 has received extensive attention and application due to its significant advantages of simple synthesis, environmental friendliness, good stability, and suitable energy band structure. However, the photocatalytic efficiency of pure ZnIn2S4 photocatalyst is usually limited, mainly due to its significantly lower development efficiency for sunlight and the large recombination of photo-generated charges. Therefore, a variety of modification technologies have been designed to improve the photocatalytic efficiency of ZnIn2S4 for hydrogen production. The present invention introduces a MnWO4 / ZnIn2S4 heterojunction, which can effectively reduce the recombination of photo-generated electrons and holes, thereby improving the photocatalytic activity; and there has been no relevant report on the use of the MnWO4 / ZnIn2S4 heterojunction as a photocatalyst for hydrogen evolution. Summary of the Invention

[0004] The present invention provides a MnWO4 / ZnIn2S4 heterojunction photocatalyst, a preparation method thereof, and an application thereof to solve the problems of the prior art.

[0005] The technical solution adopted by the present invention is as follows: A MnWO4 / ZnIn2S4 heterojunction photocatalyst, and the preparation method includes the following steps:

[0006] 1) Dissolve Mn(CH3COO)2 and NaWO4·2H2O in appropriate amounts of water respectively, and stir to make them fully dissolve to form a uniform solution;

[0007] 2) Slowly add the stirred NaWO4·2H2O solution to the stirring Mn(CH3COO)2 and continue stirring for 30 min;

[0008] 3) Put the solution obtained in step 2) into an autoclave for hydrothermal reaction. After completion, cool to room temperature, centrifuge and wash the product, and place it in an oven to dry to obtain a MnWO4 photocatalytic material;

[0009] 4) Dissolve ZnCl2, InCl3 and TAA in an appropriate amount of water according to a certain ratio, and stir to fully dissolve them to form a uniform precursor solution;

[0010] 5) Place a certain amount of MnWO4 into the precursor solution in step 4), and stir to fully dissolve it to form a uniform solution;

[0011] 6) Put the solution obtained in step 5) into an autoclave for hydrothermal reaction. After completion, cool it to room temperature, centrifuge and wash the product, and dry it in an oven to obtain the MnWO4 / ZnIn2S4 photocatalytic material.

[0012] For the above-mentioned MnWO4 / ZnIn2S4 heterojunction photocatalyst, in step 1), the molar ratio of Mn(CH3COO)2 and NaWO4·2H2O is 1:1.

[0013] For the above-mentioned MnWO4 / ZnIn2S4 heterojunction photocatalyst, in step 3), the hydrothermal reaction temperature is 150 °C and the reaction time is 3 h.

[0014] For the above-mentioned MnWO4 / ZnIn2S4 heterojunction photocatalyst, in step 4), the ratio of ZnCl2, InCl3 and TAA is 1:2:4.

[0015] For the above-mentioned MnWO4 / ZnIn2S4 heterojunction photocatalyst, in step 5), the molar ratio of MnWO4 to ZnIn2S4 is 1:20 - 3:20.

[0016] For the above-mentioned MnWO4 / ZnIn2S4 heterojunction photocatalyst, in step 6), the hydrothermal reaction temperature is 180 °C and the reaction time is 24 h.

[0017] Application of the above-mentioned MnWO4 / ZnIn2S4 heterojunction photocatalyst in photocatalytic water hydrogen evolution.

[0018] For the above-mentioned application, the method is as follows. Add the above-mentioned MnWO4 / ZnIn2S4 heterojunction photocatalyst into a mixed solution of deionized water, triethanolamine and chloroplatinic acid, continuously introduce argon at a constant flow rate to obtain a relatively vacuum environment, and carry out photocatalytic hydrogen evolution under visible light irradiation conditions.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention prepares a MnWO4 / ZnIn2S4 heterojunction photocatalyst by a hot solvent method, which has a larger specific surface area, stronger light absorption ability, and higher separation rate of photo-generated carriers, thus significantly improving the visible light response of the catalyst and enhancing the photocatalytic activity.

[0021] 2. The MnWO4 / ZnIn2S4 heterojunction photocatalyst prepared by the present invention has stronger photocatalytic reduction ability and participates in the catalytic reaction, which is an effective way to improve the visible light catalytic activity.

[0022] 3. The MnWO4 / ZnIn2S4 heterojunction photocatalyst prepared by the present invention has good photocatalytic hydrogen evolution performance, and this method is simple, convenient, low-cost, mild in conditions, and conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 X-ray diffraction patterns of the ZnIn2S4, MnWO4, MZ-5, MZ-10, and MZ-15 (representing the molar ratios of Mn ions to Zn ions of 1:20, 1:10, and 3:20, respectively) photocatalysts prepared in Example 1.

[0024] Figure 2 Hydrogen evolution activity comparison diagram of the ZnIn2S4, MnWO4, MZ-5, MZ-10, and MZ-15 photocatalysts prepared in Example 1 for water decomposition. DETAILED DESCRIPTION OF THE INVENTION

[0025] Example 1

[0026] The preparation method of the MnWO4 / ZnIn2S4 heterojunction photocatalyst is as follows:

[0027] 1. Preparation of the MnWO4 photocatalyst

[0028] First, 1 mmol of Mn(CH3COO)2 and 1 mmol of Na2WO4·2H2O are respectively dissolved in 25 ml of deionized water, and stirred thoroughly for 30 min. The stirred Na2WO4·2H2O solution is slowly added to the continuously stirred Mn(CH3COO)2 solution, and stirred continuously for 30 min. Subsequently, the mixed solution is transferred into an 80 mL stainless steel autoclave with a Teflon liner and maintained at 423 K for 3 h. The final product is cooled to room temperature, washed three times with deionized water and anhydrous ethanol respectively, and dried in an oven at 60 °C for 12 h to obtain a pure sample of the MnWO4 photocatalyst.

[0029] 2. Preparation of the ZnIn2S4 catalyst

[0030] The pure ZnIn2S4 catalyst material was synthesized according to the literature reports, and the preparation method is as follows: When directly synthesizing by the hydrothermal method, first add ZnCl2 (0.4 mmol) and InCl3 (0.8 mmol) to 36 ml of distilled water and stir for 30 minutes, then add TAA (1.6 mmol) to the mixture solution and continuously stir for 30 minutes, and then transfer it to an 80 mL polytetrafluoroethylene-lined stainless steel autoclave and maintain it at a temperature of 453 K for 24 hours. Cool the final product to room temperature, wash it three times by centrifugation with deionized water and ethanol, and dry it overnight in an atmosphere of 333 K to obtain pure ZnIn2S4.

[0031] 3. Preparation of MnWO4 / ZnIn2S4 heterojunction photocatalyst

[0032] Dissolve ZnCl2 (0.4 mmol), InCl3 (0.8 mmol), and TAA (2.4 mmol) in 36 ml of deionized water, stir for 30 min, then add a certain proportion of MnWO4 (0.02 mmol, 0.04 mmol, 0.06 mmol) to it and continuously stir for 30 min. Subsequently, transfer it to an 80 mL Teflon-lined stainless steel autoclave and maintain it at 453 K for 24 h. Cool the final product to room temperature, wash it three times with deionized water and absolute ethanol respectively, and dry it in an oven at 60 °C for 12 h to obtain the MnWO4 / ZnIn2S4 (MZ-X) heterojunction photocatalyst, which is labeled as MZ-5, MZ-10, and MZ-15 respectively according to the molar ratio of MnWO4 to ZnIn2S4.

[0033] Figure 1X-ray diffraction patterns of the ZnIn2S4, MnWO4, MZ-5, MZ-10, and MZ-15 photocatalysts prepared for Example 1. In the figure, at 2θ = 21.6°, 27.7°, 30.4°, 47.2°, 52.4°, and 56.3°, they respectively correspond to the (006), (102), (104), (110), (112), and (202) hexagonal phases of ZnIn2S4 (standard card PDF#65-2023). It was found from the XRD pattern that no characteristic peaks of other impurities were observed, indicating that the purity of the pure ZnIn2S4 photocatalytic material is very high. The XRD pattern of the pure MnWO4 has high crystallinity. In the diffraction spectrum of pure MnWO4, the characteristic peaks at 15.3°, 18.4°, 23.6°, 24°, 29.8°, 30.3°, 36°, and 37.2° are respectively the (010), (100), (011), (110), (-111), (111), (021), and (200) crystal planes, and it is in good agreement with the standard XRD pattern (JCPDS No.72-0478). At the same time, no other impurity peaks were detected, indicating that the purity of the MnWO4 catalyst material is very high. All XRD patterns of the MnWO4 / ZnIn2S4 heterojunction composite catalyst material show the characteristic peaks of hexagonal ZnIn2S4 and MnWO4, indicating that different amounts of ZnIn2S4 and MnWO4 do not affect the crystal structure of the composite material. In addition, the intensity of the diffraction peak increases with the increase in the content of MnWO4, indicating the successful preparation of the MnWO4 / ZnIn2S4 heterostructure catalyst material.

[0034] Example 2

[0035] Application of the MnWO4 / ZnIn2S4 heterojunction photocatalyst in photocatalytic water splitting for hydrogen evolution under light irradiation:

[0036] 1) At normal temperature and pressure, add 3 mL of TEOA (7.2 mmol / mL) into a container, add 15 μL of an aqueous solution of chloroplatinic acid with a concentration of 0.75 wt%, and then add 20 mg of the ZnIn2S4, MnWO4, MZ-5, MZ-10, and MZ-15 photocatalysts prepared in Example 1. Ultrasonic for 10 min to obtain a dispersion solution; pass argon into the container at a rate of 40 mL / min for 30 min, seal the container, and under visible light irradiation conditions, take 1000 μL of the gas in the container every 30 min with a microsyringe, and use gas chromatography separation technology to detect the composition of the sample gas and determine the hydrogen evolution concentration.

[0037] 2) Figure 2It is a graph of the hydrogen production amount-time curve for photocatalytic water splitting of different samples, showing the broken line graphs of the hydrogen production amount of pure ZnIn2S4, pure MnWO4, and composite samples MZ-5, MZ-10, and MZ-15 for photocatalytic water splitting over time. The results show that the hydrogen production amount of all photocatalyst samples increases linearly with the increase of time. The hydrogen production rate of the composite MZ-10 catalyst sample is 17.4 mmol / g / h, which is about 3.5 times that of pure ZnIn2S4. This indicates that the MZ-10 photocatalyst has relatively good activity. It shows that after the formation of a heterojunction between MnWO4 and ZnIn2S4, the ability of photo-generated electron transfer is relatively strong, and the electron-hole has relatively strong redox ability.

Claims

1. A MnWO4 / ZnIn2S4 heterojunction photocatalyst, characterized in that: The preparation method comprises the following steps: 1) Dissolve Mn(CH3COO)2 and NaWO4·2H2O in appropriate amount of water respectively, and stir to fully dissolve them to form a uniform solution; 2) Slowly add the stirred NaWO4·2H2O solution into the stirring Mn(CH3COO)2 and continue stirring for 30 min; 3) placing the solution obtained in step 2) into an autoclave for hydrothermal reaction, cooling to room temperature after the reaction, centrifuging and washing the product, and drying in an oven to obtain a MnWO4 photocatalytic material; 4) Dissolve ZnCl2, InCl3 and TAA in a proper amount of water in a certain proportion, and stir to fully dissolve them to form a uniform precursor solution; 5) placing a certain amount of MnWO4 in the precursor solution of step 4), stirring to fully dissolve it to form a uniform solution; 6) The solution obtained in step 5) is placed in an autoclave for hydrothermal reaction. After the reaction is completed, the product is cooled to room temperature, washed by centrifugation, and dried in an oven to obtain a MnWO4 / ZnIn2S4 photocatalytic material.

2. The MnWO4 / ZnIn2S4 heterojunction photocatalyst according to claim 1, characterized in that: In step 1), the molar ratio of Mn(CH3COO)2 and NaWO4·2H2O is 1:

1.

3. The MnWO4 / ZnIn2S4 heterojunction photocatalyst according to claim 1, characterized in that: In step 3), the hydrothermal reaction temperature is 150° C. and the reaction time is 3 h.

4. The MnWO4 / ZnIn2S4 heterojunction photocatalyst according to claim 1, characterized in that: In step 4), the ratio of ZnCl2, InCl3 and TAA is 1:2:

4.

5. The MnWO4 / ZnIn2S4 heterojunction photocatalyst according to claim 1, characterized in that: In step 5), the molar ratio of MnWO4 to ZnIn2S4 is 1:20-3:

20.

6. The MnWO4 / ZnIn2S4 heterojunction photocatalyst according to claim 1, characterized in that: In step 6), the hydrothermal reaction temperature is 180° C. and the reaction time is 24 h.

7. Use of the MnWO4 / ZnIn2S4 heterojunction photocatalyst according to any one of claims 1 to 6 in photocatalytic water hydrogen evolution.

8. The use according to claim 7, characterized in that: The method is as follows: adding the MnWO4 / ZnIn2S4 heterojunction photocatalyst described in any one of claims 1 to 6 to a mixed solution of deionized water, triethanolamine and chloroplatinic acid, continuously introducing argon gas at a constant flow rate to obtain a relatively vacuum environment, and performing photocatalytic hydrogen evolution under visible light irradiation conditions.

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