A method for preparing MOF-derived ZnCdS photocatalyst and its application

Abstract

This invention discloses a method for preparing a MOF-derived ZnCdS photocatalyst. The method involves preparing ZnCdS powder and Ni2P composite powder separately, then adding the ZnCdS powder and Ni2P composite powder to anhydrous ethanol and mixing thoroughly. The solution is then heated at 90-120°C until it reaches a viscous state, followed by vacuum drying to obtain the MOF-derived ZnCdS photocatalyst. The catalyst prepared by this method has a large specific surface area and good structural stability. This catalyst exhibits significant catalytic effect and reusability in photocatalytic water splitting for hydrogen production. In the total water splitting reaction, high hydrogen production efficiency can be obtained without the use of a sacrificial agent. The catalyst of this invention has excellent application prospects in photocatalytic water splitting for hydrogen production.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a method for preparing MOF-derived ZnCdS photocatalyst and its application in photocatalytic water splitting for hydrogen production or total water splitting. Background Technology

[0002] Hydrogen is considered a very clean energy source and an excellent alternative to fossil fuels. Heavy reliance on fossil fuels will lead to an energy crisis and environmental damage. To replace fossil fuels, renewable energy sources are being developed. Hydrogen energy, as a clean and efficient energy medium, has attracted much attention because its combustion produces only water vapor and no harmful gases. This makes hydrogen a very promising energy source with great potential in mitigating climate change and solving energy problems. Converting solar energy into hydrogen fuel is a very attractive technology. Photocatalytic water splitting for hydrogen production has been a research direction in recent years. The efficiency and rate of photocatalytic water splitting for hydrogen production are affected by the choice and performance of the catalyst. Therefore, developing efficient and stable catalysts is crucial. In recent years, some novel catalysts such as titanium dioxide (TiO2) and silicon dioxide (SiO2) have been extensively studied. However, they face many challenges due to their poor stability and the need for further efficiency improvement in practical experiments. Metal-organic frameworks, due to their tunable structure, are often used as catalysts for photocatalytic water splitting. However, the coordination bonds between metal nodes and organic ligands are fragile and unstable. While the metal-organic framework (MOF) template method, which involves sulfidation followed by ZnCdS synthesis, can retain its high specific surface area, the severe photocorrosion problem of sulfides remains unresolved, failing to meet the requirements and expectations of high-performance photocatalysts. This significantly hinders its application in photocatalytic water splitting for hydrogen production. Therefore, supported co-catalysts such as Pt, Pd, and Ru are essential for most photocatalysts in hydrogen evolution reaction (HER). However, the scarcity, high value, and high cost of precious metal co-catalysts limit their use in photocatalysts. Furthermore, most research focuses on improving single reduction or oxidation reactions, requiring the addition of expensive sacrificial agents to promote these reactions; and there is little in-depth research on the overall water splitting route. Summary of the Invention

[0003] This invention provides a method for preparing MOF-derived ZnCdS photocatalysts, the specific steps of which are as follows:

[0004] (1) Under stirring conditions, zinc source-methanol solution is added to 2-methylimidazolium-methanol solution for reaction. The reaction product is separated into solid and liquid. The solid is washed and dried. The dried product, cadmium source, and thiourea are placed in water, mixed, and reacted at 200-250℃ for 15-20h. The solid is then separated into solid and liquid. The solid is washed and dried and ground to obtain ZnCdS powder.

[0005] The molar ratio of zinc source to 2-methylimidazole is 1:7-9, and the reaction is stirred for 20-25 h. The molar ratio of zinc source to cadmium source is (2-3):(0.1-0.3), and the molar ratio of thiourea to cadmium source is 20:1-3.

[0006] (2) Add nickel source, aluminum source, ammonium fluoride and urea to deionized water, stir and mix well, react at 100-150℃, separate solid and liquid, wash and dry the solid, grind to obtain precursor powder, place the precursor powder and sodium hypophosphite in two ceramic boats respectively, react at 250-350℃ in nitrogen atmosphere, wash and dry the reaction product, grind to obtain Ni2P composite powder;

[0007] The molar ratio of nickel source to aluminum source is 4:1-2, the amount of ammonium fluoride added is 50-60% of the mass of nickel source, and the amount of urea added is 120-140% of the mass of nickel source;

[0008] (3) Add ZnCdS powder and Ni2P composite powder to anhydrous ethanol, heat and stir the solution at 90-120℃ until it becomes viscous, and then dry it under vacuum to obtain MOF-derived ZnCdS photocatalyst.

[0009] The mass ratio of ZnCdS powder to Ni2P powder is 20:1-5.

[0010] Another objective of this invention is to apply the MOF-derived ZnCdS photocatalyst prepared by the above method to hydrogen production through photocatalytic water splitting or total water splitting. Specifically, the MOF-derived ZnCdS photocatalyst is added to a photoreaction vessel containing water, and hydrogen is produced through the reaction under light. Hydrogen and oxygen are produced in the total water splitting reaction.

[0011] Compared with the prior art, the present invention has the following advantages and effects:

[0012] The catalyst prepared by the method of this invention has the characteristics of large specific surface area and good structural stability. The catalyst has significant catalytic effect and reusability in photocatalytic water splitting for hydrogen production. In the total water splitting reaction, high hydrogen production efficiency can be obtained without the use of sacrificial agents. The catalyst of this invention has a good application prospect in photocatalytic water splitting for hydrogen production. Attached Figure Description

[0013] Figure 1 SEM image of Ni2P composite powder;

[0014] Figure 2 SEM image of MOF-derived ZnCdS photocatalyst;

[0015] Figure 3 XPS image of the MOF-derived ZnCdS photocatalyst of this invention;

[0016] Figure 4 The effect of MOF-derived ZnCdS photocatalyst on water splitting;

[0017] Figure 5 Rendering of the water splitting and hydrogen production cycle using MOF-derived ZnCdS photocatalyst;

[0018] Figure 6 XRD patterns before and after use of MOF-derived ZnCdS photocatalyst. Detailed Implementation

[0019] To clearly illustrate the content of this invention, the following examples provide a more detailed description of the invention. However, the scope of protection of this invention is not limited to the content described. All chemical reagents used in the examples are of analytical grade. Example 1

[0020] 1. Weigh 2 mmol of zinc nitrate and 16 mmol of 2-methylimidazole and add them to 25 mL of methanol. Stir for 20 min. Slowly add the 2-methylimidazole-methanol solution to the zinc nitrate-methanol solution and stir for 24 h to obtain a milky white suspension. Centrifuge, collect the solid, wash the solid three times with methanol, and dry it under vacuum at 60 °C for 24 h. Add the dried solid powder and 0.3 mmol of cadmium nitrate to 12 mL of an aqueous solution containing 2 mmol of thiourea. Mix ultrasonically for 10 min. Transfer the mixture to a stainless steel reactor with a polytetrafluoroethylene liner and hydrothermally react at 220 °C for 18 h. After cooling to room temperature, centrifuge. Wash the solid three times with anhydrous ethanol and deionized water, dry it under vacuum at 60 °C, and grind it to obtain ZnCdS powder.

[0021] 2. Add 1.40g nickel nitrate, 0.60g aluminum nitrate, 0.77g ammonium fluoride, and 1.92g urea to 80mL deionized water and stir for 1 hour to mix thoroughly. Transfer the mixture to a stainless steel reactor with a polytetrafluoroethylene liner and hydrothermally react at 120℃ for 12 hours. After cooling to room temperature, centrifuge the mixture. Wash the solid three times with deionized water, vacuum dry and grind it at 60℃, and place it in two separate ceramic boats (mass ratio 1:3) along with sodium hypophosphite. Place the ceramic boat containing sodium hypophosphite in a tube furnace near the gas inlet. Heat the furnace to 300℃ at a rate of 5℃ / min under a nitrogen atmosphere and hold for 2 hours. Wash the resulting black solid three times with deionized water, vacuum dry it at 60℃, and grind it to obtain Ni2P composite powder. The SEM image of the Ni2P composite powder is shown below. Figure 1 ;

[0022] 3. Take 0.1 g of ZnCdS powder and 0.005 g of Ni2P composite powder, add them to 40 mL of anhydrous ethanol under stirring, stir for 12 h, heat the solution at 100 °C until it becomes viscous, and vacuum dry at 60 °C to obtain the MOF-derived ZnCdS photocatalyst. Its SEM image is shown below. Figure 2 ; Figure 3 The presence of Zn, Cd, S, Ni, and P elements in the catalyst indicates its successful synthesis.

[0023] 4. Disperse 10 mg of the catalyst obtained in step 3 in 50 mL of a solution containing 0.35 mol / L Na₂S·9H₂O and 0.25 mol / L Na₂SO₃, then sonicate for 10 min. Transfer the solution to a Pyrex top-illuminated quartz window container. Evacuate the reactor for 30 min before the photocatalytic experiment. Use a 300 W xenon lamp equipped with a filter (λ>400 nm) as the light source. Maintain the reaction temperature at 5 °C. The gas sampling port of the system is directly connected to a gas chromatograph, and samples are automatically taken every 30 min to measure the product gas online. The photocatalytic hydrogen production rate of water splitting within 3 h is as high as 72.8 mmol / (g·h). See [link to relevant documentation]. Figure 4 .

[0024] The Ni2P composite powder obtained in step 2 was used as the catalyst in Comparative Example 1 for photocatalytic water splitting. The photocatalytic hydrogen production rate from water splitting reached 0.2 mmol / (g·h) within 3 hours. Figure 4 ;

[0025] Using the ZnCdS powder prepared in step 1 as a catalyst in Comparative Example 2, the photocatalytic water splitting reaction was successfully completed. The hydrogen production rate from water splitting reached 56.6 mmol / (g·h) within 3 hours. Figure 4 ;

[0026] Meanwhile, the above catalyst was subjected to a total water splitting experiment without the addition of any sacrificial agent, and all other conditions were the same as above. The results are shown below. Figure 5 The catalysts in Comparative Examples 1-2 did not catalyze the complete water splitting, therefore no results were shown in the figure. Example 2

[0027] 1. Same as step 1 in Example 1;

[0028] 2. Same as step 2 in Example 1;

[0029] 3. Take 0.1g of ZnCdS powder and 0.01g of Ni2P composite powder, add them to 40mL of anhydrous ethanol under stirring and stir for 12h. Then heat the solution at 100℃ until it becomes viscous and dry it under vacuum at 60℃ to obtain MOF-derived ZnCdS photocatalyst.

[0030] 4. The catalyst prepared in this example was applied to a photocatalytic water splitting reaction. The experimental conditions were the same as in Example 1. The results showed that the photocatalytic hydrogen production rate from water splitting reached 82.6 mmol / (g·h) within 3 hours. (See [link to example]). Figure 4 ;

[0031] Simultaneously, a total water splitting experiment was conducted without adding any sacrificial agent, and all other conditions were the same as above. The results are shown below. Figure 5 . Example 3

[0032] 1. Same as step 1 in Example 1;

[0033] 2. Same as step 2 in Example 1;

[0034] 3. Take 0.1g of ZnCdS powder and 0.015g of Ni2P composite powder, add them to 40mL of anhydrous ethanol under stirring and stir for 12h. Then heat the solution at 100℃ until it becomes viscous and dry it under vacuum at 60℃ to obtain MOF-derived ZnCdS photocatalyst.

[0035] 4. The catalyst prepared in this example was applied to a photocatalytic water splitting reaction. The experimental conditions were the same as in Example 1. The results showed that the photocatalytic hydrogen production rate from water splitting reached 96.4 mmol / (g·h) within 3 hours. (See [link to example 1]). Figure 4 ;

[0036] Simultaneously, a total water splitting experiment was conducted without adding any sacrificial agent, and all other conditions were the same as above. The results are shown below. Figure 5 . Example 4

[0037] 1. Same as step 1 in Example 1;

[0038] 2. Same as step 2 in Example 1;

[0039] 3. Take 0.1g of ZnCdS powder and 0.02g of Ni2P composite powder, add them to 40mL of anhydrous ethanol under stirring and stir for 12h. Then heat the solution at 100℃ until it becomes viscous and dry it under vacuum at 60℃ to obtain MOF-derived ZnCdS photocatalyst.

[0040] 4. The catalyst prepared in this example was applied to a photocatalytic water splitting reaction. The experimental conditions were the same as in Example 1. The results showed that the photocatalytic hydrogen production rate from water splitting reached 89.1 mmol / (g·h) within 3 hours. (See [link]). Figure 4 ;

[0041] Simultaneously, a total water splitting experiment was conducted without adding any sacrificial agent, and all other conditions were the same as above. The results are shown below. Figure 5 . Example 5

[0042] 1. Same as step 1 in Example 1;

[0043] 2. Same as step 2 in Example 1;

[0044] 3. Take 0.1g of ZnCdS powder and 0.025g of Ni2P composite powder, add them to 40mL of anhydrous ethanol under stirring and stir for 12h. Then heat the solution at 100℃ until it becomes viscous and dry it under vacuum at 60℃ to obtain MOF-derived ZnCdS photocatalyst.

[0045] 4. The catalyst prepared in this example was applied to a photocatalytic water splitting reaction. The experimental conditions were the same as in Example 1. The results showed that the photocatalytic hydrogen production rate from water splitting reached 86.1 mmol / (g·h) within 3 hours. (See [link]). Figure 4 ;

[0046] Simultaneously, a total water splitting experiment was conducted without adding any sacrificial agent, and all other conditions were the same as above. The results are shown below. Figure 5 .

[0047] The above embodiments show that the MOF-derived ZnCdS of the present invention is more effective than the comparative catalyst in photocatalytic water splitting for hydrogen production.

[0048] Example 6: Recycling Experiment of MOF-Derived ZnCdS Catalyst with Supported Co-catalyst

[0049] The catalyst from Example 3, after reacting for 3 hours, was used to conduct a 12-hour photocatalytic hydrogen production experiment. Before the third and fifth cycles, 0.35 mol / L Na2S·9H2O and 0.25 mol / L Na2SO3 sacrificial agents were added to complete the cycle experiment.

[0050] See results Figure 5After five cycles, the hydrogen production rate decreased slightly, but after the fifth cycle, the hydrogen production rate remained at 87 mmol / g / h, which was 90.24% of the initial rate. After five cycles, the catalyst was recovered and washed three times with deionized water, dried under vacuum at 60°C for 12 h, and ground. X-ray diffraction (XRD) analysis was performed on the catalyst before and after the reaction. The results are as follows: Figure 6 As shown, the XRD patterns before and after the reaction did not change significantly, and the structure and morphology remained almost unchanged, verifying its excellent stability.

Claims

1. Application of MOF derived ZnCdS photocatalyst in hydrogen production by water photolysis or overall water splitting without sacrificial agent, characterized in that, The MOF-derived ZnCdS photocatalyst is prepared as follows: (1) under stirring, zinc source-methanol solution is added to 2-methyl imidazole-methanol solution for reaction, the reaction product is separated by solid-liquid separation, the solid is washed and dried, the dried product, cadmium source and thiourea are placed in water, mixed and reacted at 200-250°C for 15-20h, then separated by solid-liquid separation, the solid is washed and dried, and grinded to obtain ZnCdS powder; (2) nickel source, aluminum source, ammonium fluoride and urea are added to deionized water, stirred and mixed, then reacted at 100-150°C, separated by solid-liquid separation, the solid is washed and dried, and grinded to obtain precursor powder, the precursor powder and sodium hypophosphite are respectively placed in two porcelain boats, reacted at 250-350°C under nitrogen atmosphere, the reaction product is washed and dried, and grinded to obtain Ni2P composite powder; (3) ZnCdS powder and Ni2P composite powder are added to anhydrous ethanol, mixed, heated to viscous solution at 90-120°C, and vacuum dried to obtain the MOF-derived ZnCdS photocatalyst.

2. Use according to claim 1, characterized in that: In step (1), the molar ratio of zinc source to 2-methyl imidazole is 1:7-9, the stirring reaction is carried out for 20-25h, the molar ratio of zinc source to cadmium source is 2-3:0.1-0.3, and the molar ratio of thiourea to cadmium source is 20:1-3.

3. Use according to claim 1, characterized in that: The molar ratio of nickel source to aluminum source is 4:1-2, the addition amount of ammonium fluoride is 50-60% of the mass of nickel source, and the addition amount of urea is 120-140% of the mass of nickel source.

4. Use according to claim 1, characterized in that: The mass ratio of precursor powder to sodium hypophosphite is 1:2-4, and the phosphating time is 1-3h.

5. The use according to claim 1, characterized in that: The mass ratio of ZnCdS powder to Ni2P composite powder is 20:1-5.

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