Preparation method and application of ZnSe / MnWO4 heterojunction photocatalyst

Abstract

The invention belongs to the technical field of photocatalytic materials, and particularly relates to a preparation method and application of a ZnSe / MnWO4 heterojunction photocatalyst. The ZnSe / MnWO4 heterojunction photocatalyst synthesized by placing ZnSe prepared through a solvothermal reaction into a MnWO4 solution prepared through the solvothermal reaction and carrying out the solvothermal reaction again can be applied to the field of photocatalytic reduction of CO2. Compared with an existing photocatalyst, the ZnSe / MnWO4 heterojunction has good structural performance and stability, and a built-in electric field at the heterojunction interface can accelerate separation and transfer of carriers and enhance adsorption and activation of CO2, so that the activity of photocatalytic reduction of CO2 is enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalytic materials, and specifically relates to a preparation method and application of a ZnSe / MnWO4 heterojunction photocatalyst. Background Art

[0002] The rapid development of human society has led to an increasing demand for fossil fuels, resulting in a significant increase in CO2 emissions. Current scientific research is mainly focused on developing effective methods to convert CO2 with high dissociation energy into valuable chemical products. Among the many proposals, the scheme of using solar energy to catalyze CO2 conversion has great potential. However, the efficiency of current photocatalysts in photocatalytic reduction of CO2 using solar energy is relatively low, which is difficult to meet human demand for energy.

[0003] ZnSe is widely used in the field of photocatalytic reduction of CO2 due to its excellent conductivity, stability, narrow bandgap and small resistivity. However, pure ZnSe faces the problems of low solar energy utilization and high carrier recombination rate. Therefore, synthetic heterojunction is an effective method to improve the solar energy utilization of ZnSe and reduce the recombination of electron-hole pairs. The present invention introduces ZnSe / MnWO4 to form a heterojunction, which can improve the efficiency of photogenerated electron-hole separation, thereby improving the photocatalytic activity; and there is no related report on the use of ZnSe / MnWO4 heterojunction as a photocatalyst to reduce CO2. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a preparation method and application of a ZnSe / MnWO4 heterojunction photocatalyst.

[0005] The technical solution adopted by the present invention is:

[0006] A method for preparing a ZnSe / MnWO4 heterojunction photocatalyst comprises the following steps:

[0007] 1) Selenium powder, zinc chloride and sodium hydroxide are respectively placed in a beaker filled with an equal amount of deionized water, and after being fully stirred to be evenly dispersed, the zinc chloride solution is first slowly poured into the beaker filled with selenium powder and continued to stir. After being fully stirred, the sodium hydroxide solution is slowly poured into the mixture of selenium powder and zinc chloride. After being fully stirred, the mixture is placed in an autoclave for hydrothermal reaction. After the reaction is completed, a yellow precipitate is obtained. The sample is washed and dried to obtain ZnSe;

[0008] 2) Dissolve manganese acetate and sodium tungstate in equal amounts of deionized water, stir until completely dissolved, and then continue stirring, add the sodium tungstate solution to the manganese acetate solution, place the mixed solution in an autoclave for hydrothermal reaction, and obtain a brown precipitate. Wash the sample and dry it to obtain MnWO4;

[0009] 3) The ZnSe obtained in step 1) is dispersed in deionized water and stirred until it turns light yellow. The MnWO4 obtained in step 2) is placed in an autoclave filled with a ZnSe solution for hydrothermal reaction. After the reaction, the sample is washed and dried to obtain a ZnSe / MnWO4 heterojunction photocatalyst.

[0010] Furthermore, in the above preparation method, in step 1), the amount of selenium powder used is 0.158 g, the amount of zinc chloride used is 0.271 g, the amount of sodium hydroxide used is 0.64 g, and the total amount of deionized water used is 60 mL.

[0011] Furthermore, in the above preparation method, in step 1), the temperature of the hydrothermal reaction is 180° C. and the reaction time is 24 h.

[0012] Furthermore, in the above preparation method, in step 2), the amount of manganese acetate used is 0.491 g, the amount of sodium tungstate used is 0.6597 g, and the total amount of deionized water used is 60 mL.

[0013] Furthermore, in the above preparation method, in step 2), the temperature of the hydrothermal reaction is 150° C. and the reaction time is 6 h.

[0014] Furthermore, in the above preparation method, in step 3), the molar ratio of ZnSe to MnWO4 is 50%.

[0015] Preferably, in the above preparation method, in step 3), the amount of ZnSe used is 0.145 g, the amount of MnWO4 used is 0.303 g, and the amount of deionized water used is 60 mL.

[0016] Furthermore, in the above preparation method, in step 3), the temperature of the hydrothermal reaction is 180° C. and the reaction time is 12 h.

[0017] Furthermore, in the above-mentioned preparation method, in steps 1), 2) and 3), the stirring method is to use a magnetic stirrer for stirring.

[0018] Furthermore, in the above-mentioned preparation method, in steps 1), 2) and 3), the drying temperature is 60° C. and the drying time is 6 hours.

[0019] Application of the ZnSe / MnWO4 heterojunction photocatalyst prepared by any of the preparation methods described above in photocatalytic reduction of CO2.

[0020] Further, the above application method is as follows:

[0021] 1) Take the ZnSe / MnWO4 heterojunction photocatalyst and spread it evenly on the culture dish, then add deionized water, and then dry it so that the catalyst is evenly spread on the culture dish;

[0022] 2) injecting deionized water into the bottom of a transparent glass reaction container, then transferring the dry culture dish into the glass reaction container, and sealing the glass reaction container with a quartz glass cover; evacuating the glass reaction container, and then filling it with CO2, and repeating the operation four times; photocatalytically reducing CO2 under visible light irradiation conditions.

[0023] Furthermore, in the above application, in step 1), the amount of ZnSe / MnWO4 heterojunction photocatalyst used is 10 mg, and the culture dish area is 2 cm 2 .

[0024] Furthermore, in the above application, in step 2), the amount of deionized water used is 500 μL.

[0025] The beneficial effects of the present invention are:

[0026] 1. The ZnSe / MnWO4 heterojunction photocatalyst prepared by the solvothermal method of the present invention has a two-dimensional structure, which can increase the specific surface area, improve the separation efficiency of carriers, and enhance the photocatalytic activity.

[0027] 2. The ZnSe / MnWO4 heterojunction photocatalyst prepared by the present invention has a stronger ability to absorb visible light and is an effective way to improve the visible light catalytic activity.

[0028] 3. The ZnSe / MnWO4 heterojunction photocatalyst prepared by the present invention has good photocatalytic reduction of CO2 performance, and the method is simple to prepare, environmentally friendly, non-toxic, low-cost, and conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 These are the X-ray diffraction patterns of ZnSe, MnWO4, and ZnSe / MnWO4 heterojunction photocatalysts.

[0030] Figure 2 This is the time curve of ZnSe, MnWO4, and ZnSe / MnWO4 heterojunction photocatalysts reducing CO2 to CO. DETAILED DESCRIPTION

[0031] Example 1

[0032] The preparation method of ZnSe / MnWO4 heterojunction photocatalyst is as follows:

[0033] 1) Selenium powder (0.158g), zinc chloride (0.271g), and sodium hydroxide (0.64g) were placed in a beaker containing an equal amount (20mL) of deionized water. After sufficient magnetic stirring, the zinc chloride solution was slowly poured into the beaker containing selenium powder and continued to be magnetically stirred. After sufficient stirring, the sodium hydroxide solution was slowly poured into the mixture of selenium powder and zinc chloride. After sufficient magnetic stirring, the mixture was placed in an autoclave for hydrothermal reaction (180°C, 24h). After the reaction, a yellow precipitate was obtained. The sample was washed and dried at 60°C for 6h to obtain ZnSe.

[0034] 2) Dissolve manganese acetate (0.491 g) and sodium tungstate (0.6597 g) in 30 mL of deionized water, respectively, and stir magnetically until completely dissolved. Then, continue to stir magnetically and add the sodium tungstate solution to the manganese acetate solution. Place the mixed solution in an autoclave for hydrothermal reaction (150°C, 6 h) to obtain a brown precipitate. Wash the sample and dry it at 60°C for 6 h to obtain MnWO4;

[0035] 3) Disperse ZnSe (0.145 g) in 60 mL of deionized water and stir magnetically until it turns light yellow. Then add 0.303 g of MnWO4 and stir magnetically evenly. Then put it into an autoclave for hydrothermal reaction (180°C, 12 h). After the reaction, wash the sample and dry it at 60°C for 6 h to obtain a ZnSe / MnWO4 heterojunction photocatalyst.

[0036] Figure 1 This is the X-ray diffraction pattern of the ZnSe / MnWO4 heterojunction photocatalyst prepared in Example 1. In the figure, characteristic diffraction peaks appear at 2θ=27.224°, 45.195°, 53.568°, 65.858° and 72.632°, corresponding to (111), (220), (331), (400) and (331) crystal planes, which is consistent with the ZnSe PDF standard card (PDF#37-1643). In the figure, characteristic diffraction peaks appear at 2θ=18.315°, 23.516°, 24.032°, 29.786°, 30.209° and 35.965°, corresponding to (100), (001), (110), (-111), (111), (021) crystal planes, which is consistent with the MnWO4 PDF standard card (PDF#10-0477). Figure 1 It can be seen that the peaks of both substances appear in the composite sample ZnSe / MnWO4, indicating that the two substances are successfully composited.

[0037] Example 2

[0038] At room temperature and pressure, 10 mg of the ZnSe / MnWO4 heterojunction photocatalyst prepared in Example 1 was placed in a culture dish (2 cm2 ) and spread it on the culture dish, then dry it in an oven at 60°C and wait for the photocatalytic performance test. Inject 500μL of deionized water into the bottom of a transparent glass reaction container, then transfer the dried culture dish to the glass reaction container, and seal the glass reaction container with a quartz glass cover. Evacuate the glass reaction container and then fill it with CO2, and repeat the operation four times. Use a 300W xenon lamp as a light source to illuminate the photocatalyst. After every 1h of illumination reaction, extract the upper gas from the container with a syringe, and use a gas chromatograph to test the carbon monoxide concentration in the upper gas, and continue to detect for 4h (one cycle).

[0039] Figure 2 This is a time curve of the sample's photocatalytic reduction of CO2 to CO. It can be seen that after 4 hours of light reaction, the CO production of ZnSe / MnWO4 is 8.897 μmol / g / h, which is 13.29 times that of pure ZnSe and 4.7 times that of pure MnWO4.

Claims

1. A method for preparing a ZnSe / MnWO4 heterojunction photocatalyst, characterized in that: The steps include: 1) Selenium powder, zinc chloride and sodium hydroxide are respectively placed in a beaker filled with an equal amount of deionized water, and after being fully stirred to be evenly dispersed, the zinc chloride solution is first slowly poured into the beaker filled with selenium powder and continued to stir. After being fully stirred, the sodium hydroxide solution is slowly poured into the mixture of selenium powder and zinc chloride. After being fully stirred, the mixture is placed in an autoclave for hydrothermal reaction. After the reaction is completed, a yellow precipitate is obtained. The sample is washed and dried to obtain ZnSe; 2) Dissolve manganese acetate and sodium tungstate in equal amounts of deionized water, stir until completely dissolved, and then continue stirring, add the sodium tungstate solution to the manganese acetate solution, place the mixed solution in an autoclave for hydrothermal reaction, and obtain a brown precipitate. Wash the sample and dry it to obtain MnWO4; 3) The ZnSe obtained in step 1) is dispersed in deionized water and stirred until it turns light yellow. The MnWO4 obtained in step 2) is placed in an autoclave filled with a ZnSe solution for hydrothermal reaction. After the reaction, the sample is washed and dried to obtain a ZnSe / MnWO4 heterojunction photocatalyst.

2. The preparation method according to claim 1, characterized in that: In step 1), the amount of selenium powder used is 0.158 g, the amount of zinc chloride used is 0.271 g, the amount of sodium hydroxide used is 0.64 g, and the total amount of deionized water used is 60 mL.

3. The preparation method according to claim 1, characterized in that: In step 2), the amount of manganese acetate used is 0.491 g, the amount of sodium tungstate used is 0.6597 g, and the total amount of deionized water used is 60 mL.

4. The preparation method according to claim 1, characterized in that: In step 3), the molar ratio of ZnSe to MnWO4 is 50%.

5. The preparation method according to claim 4, characterized in that: In step 3), the amount of ZnSe used is 0.145 g, the amount of MnWO4 used is 0.303 g, and the amount of deionized water used is 60 mL.

6. The preparation method according to claim 1, characterized in that: In step 1), the temperature of the hydrothermal reaction is 180°C and the reaction time is 24h; in step 2), the temperature of the hydrothermal reaction is 150°C and the reaction time is 6h; in step 3), the temperature of the hydrothermal reaction is 180°C and the reaction time is 12h.

7. The preparation method according to claim 1, characterized in that: In steps 1), 2) and 3), the drying temperature is 60° C. and the drying time is 6 hours.

8. Use of the ZnSe / MnWO4 heterojunction photocatalyst prepared by the preparation method according to any one of claims 1 to 7 in photocatalytic reduction of CO2.

9. The use according to claim 8, characterized in that: Here’s how: 1) Take the ZnSe / MnWO4 heterojunction photocatalyst and spread it evenly on the culture dish, then add deionized water, and then dry it so that the catalyst is evenly spread on the culture dish; 2) injecting deionized water into the bottom of a transparent glass reaction container, then transferring the dry culture dish into the glass reaction container, and sealing the glass reaction container with a quartz glass cover; evacuating the glass reaction container, and then filling it with CO2, and repeating the operation four times; photocatalytically reducing CO2 under visible light irradiation conditions.

10. The use according to claim 9, characterized in that: In step 1), the amount of ZnSe / MnWO4 heterojunction photocatalyst used is 10 mg, and the culture dish area is 2 cm 2 ; In step 2), the amount of deionized water used is 500 μL.

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