A catalyst for photocatalytic water splitting to produce hydrogen and its preparation method

Abstract

This invention belongs to the field of photocatalytic water splitting for hydrogen production, and discloses a photocatalytic water splitting catalyst and its preparation method. The catalyst is composed of ZnIn2S4 and oxygen-vacancy-rich Nb2O5, and ZnIn2S4 nanosheets are uniformly grown on the surface of oxygen-vacancy-rich Nb2O5 nanosheets. The mass percentage of ZnIn2S4 in the catalyst is controlled between 30% and 90%. (1) Prepare oxygen-vacancy-rich Nb2O5 nanosheet powder; (2) Prepare a raw material solution for preparing ZnIn2S4 nanosheets; (3) According to the mass ratio of oxygen-vacancy-rich Nb2O5 to ZnIn2S4, weigh the oxygen-vacancy-rich Nb2O5 nanosheet powder obtained in step (1) and add it to the raw material solution in step (2). After uniform dispersion, react at 80~160℃ for more than 3 hours; (4) After cooling to room temperature, centrifuge and wash the precipitate, and vacuum dry to obtain the catalyst. The catalyst of this invention enables niobium pentoxide to achieve a qualitative leap from no visible light response to visible light photocatalytic water splitting for hydrogen production, realizing a breakthrough from scratch.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic water splitting for hydrogen production, specifically relating to a catalyst for photocatalytic water splitting for hydrogen production and its preparation method. Background Technology

[0002] Niobium pentoxide (NiO) is a promising semiconductor for photocatalytic applications due to its negative conduction band position, excellent chemical and thermal stability, low cost, diverse morphologies, and environmental friendliness. However, its large band gap only allows NiO to absorb and utilize ultraviolet light, while ultraviolet light accounts for only 4.6% of sunlight, and visible light accounts for 47.7%. Therefore, the vast majority of sunlight cannot be fully and effectively utilized, leading to energy waste. Furthermore, the photogenerated electrons and holes generated by NiO upon photoexcitation quickly recombine in the bulk phase, and most cannot participate in the photocatalytic reaction, resulting in reduced activity and low efficiency in the photocatalytic water splitting for hydrogen production. Therefore, its improvement is necessary. Current research on NiO as a photocatalyst is scarce, making its development and research of significant importance and application value. Summary of the Invention

[0003] In order to solve the problems of niobium pentoxide catalysts in the prior art being unable to utilize visible light and having low efficiency in photocatalytic water splitting for hydrogen production, the present invention aims to provide a catalyst for photocatalytic water splitting for hydrogen production and its preparation method.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A photocatalytic water splitting catalyst for hydrogen production is disclosed, wherein the catalyst is composed of ZnIn2S4 and Nb2O5 rich in oxygen vacancies, and ZnIn2S4 nanosheets are uniformly grown on the surface of Nb2O5 nanoplates rich in oxygen vacancies, and the mass percentage of ZnIn2S4 in the catalyst is controlled between 30% and 90%.

[0006] Preferably, the mass percentage of ZnIn2S4 in the catalyst is 70%.

[0007] A method for preparing a catalyst for photocatalytic water splitting to produce hydrogen, comprising the following steps:

[0008] (1) Preparation of Nb2O5 nanosheet powder rich in oxygen vacancies;

[0009] (2) Prepare the raw material solution for preparing ZnIn2S4 nanosheets;

[0010] (3) According to the mass ratio of oxygen-vacancy-rich Nb2O5 to ZnIn2S4, weigh the oxygen-vacancy-rich Nb2O5 nanosheet powder obtained in step (1) and add it to the raw material liquid in step (2). After being dispersed evenly, react at 80~160 ℃ for more than 3 h.

[0011] (4) After cooling to room temperature, the precipitate is washed by centrifugation and dried under vacuum to obtain the catalyst of the present invention.

[0012] Preferably, the process of step (1) is as follows:

[0013] (1.1) Add ammonium niobate oxalate and melamine to ethanol, stir to dissolve, and then vacuum dry to obtain a solid; wherein, the molar ratio of the raw materials is ammonium niobate oxalate: melamine: ethanol = (1.0~3.0) g: (1.5~2.5) g: (15~30) mL;

[0014] (1.2) The solid obtained in step (1.1) is calcined at 500~700 °C for 4~6 h to obtain Nb2O5 nanosheet powder;

[0015] (1.3) The Nb2O5 nanosheet powder obtained in step (1.2) is calcined at 500~700 °C for 1~5 h in a nitrogen-hydrogen mixed atmosphere to obtain Nb2O5 nanosheet powder rich in oxygen vacancies.

[0016] Preferably, in step (1.1), the purity of ethanol is ≥95v.

[0017] Preferably, in steps (1.2) and (1.3), the calcination heating rate is 0.5~2 °C·min. -1 .

[0018] Preferably, step (2) is as follows: add water-soluble indium salt, water-soluble zinc salt and TAA to hydrochloric acid aqueous solution with pH=2~3, stir to dissolve, then add glycerol and stir evenly; wherein the ratio of raw materials is water-soluble indium salt: water-soluble zinc salt: TAA=2:1:(4~5), and add 70~90 mL of hydrochloric acid aqueous solution and 10~30 mL of glycerol for every 2 mmol of water-soluble indium salt.

[0019] Preferably, in step (3), the mixture is first sonicated and then stirred until it is evenly dispersed.

[0020] Preferably, in step (4), the water is used for centrifugation and washing, followed by ethanol.

[0021] Preferably, in step (4), the temperature of vacuum drying is 60~120 ℃.

[0022] Beneficial effects: The catalyst of this invention can achieve a qualitative leap in the photocatalytic hydrogen production rate of niobium pentoxide from no visible light response to visible light photocatalytic water splitting (niobium pentoxide from no photocatalytic activity under visible light to as high as 3.74 mmol·g). -1 ·h -1 The photocatalytic hydrogen production rate of this invention represents a breakthrough from nothing to something, turning the impossible into possible. The preparation steps of the catalyst are simple, the conditions are mild, the equipment requirements are low, the raw material cost is low, and it is easy to carry out industrial mass production. This invention is expected to solve the energy problem as soon as possible and has potential prospects for large-scale industrial application. Attached Figure Description

[0023] Figure 1 Example 1: Scanning electron microscope (SEM) image of Nb2O5 prepared in step (2).

[0024] Figure 2 Scanning electron microscope (SEM) image of the 70% ZnIn2S4 / Nb2O5 composite photocatalyst with oxygen vacancies prepared in Example 4.

[0025] Figure 3 Transmission electron microscopy (TEM) image of the 70% ZnIn2S4 / Nb2O5 composite photocatalyst with oxygen vacancies prepared in Example 4.

[0026] Figure 4 X-ray photoelectron spectroscopy (XPS) of 70% ZnIn2S4 / Nb2O5 containing oxygen vacancies prepared in Example 4.

[0027] Figure 5 X-ray diffraction (XRD) spectra of Nb2O5 prepared in step (2) of Example 4, 70% ZnIn2S4 / Nb2O5 with oxygen vacancies prepared in Example 4, and ZnIn2S4 prepared in Comparative Example 1.

[0028] Figure 6 Electron paramagnetic resonance (EPR) spectra of Nb2O5 prepared in step (2) of Example 4, Nb2O5 rich in oxygen vacancies prepared in step (3) of Example 4, 70% ZnIn2S4 / Nb2O5 containing oxygen vacancies prepared in Example 4, and pure ZnIn2S4 prepared in Control Example 1.

[0029] Figure 7 Hydrogen production rate graphs of pure Nb2O5 prepared in Examples 1-5, Nb2O5 rich in oxygen vacancies, 10-90% ZnIn2S4 / Nb2O5 composite samples, and pure ZnIn2S4 prepared in Control Example 1.

[0030] Figure 8Cyclic stability test of 70% ZnIn2S4 / Nb2O5 with oxygen vacancies prepared in Example 4. Detailed Implementation

[0031] To make the present invention clearer and more explicit, the present invention will be further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0032] Example 1

[0033] A method for preparing a catalyst for photocatalytic water splitting to produce hydrogen, comprising the following steps:

[0034] (1) Measure 15 mL of anhydrous ethanol and place it in a clean beaker. Weigh 2.0 g of ammonium niobate oxalate and 2.0 g of melamine and add them to the beaker. Stir and dissolve for 12 h, then place it in a vacuum drying oven and dry overnight at 60 °C.

[0035] (2) The solid obtained in step (1) is placed in a crucible and calcined in a muffle furnace at 550 °C for 4 h, with a heating rate of 2 °C·min. -1 The white powder obtained after calcination is Nb2O5;

[0036] (3) Weigh 200 mg of the Nb2O5 powder obtained in step (2) and place it in a porcelain boat. Calcine it in a tube furnace at 550 °C for 3 h in a nitrogen-hydrogen mixed atmosphere (volume ratio, N2:H2=8:2), with a heating rate of 2 °C·min. -1 After calcination, the resulting gray powder is Nb2O5 rich in oxygen vacancies.

[0037] (4) Weigh 0.540 g of InCl3·4H2O, 0.136 g of ZnCl2 and 0.300 g of TAA (thioacetamide) and place them in a single-necked flask. Add 80 mL of hydrochloric acid aqueous solution (pH 2.5) and stir to dissolve. Then add 20 mL of glycerol and stir until homogeneous.

[0038] (5) Weigh 0.014 g of the oxygen-rich Nb2O5 powder obtained in step (3) and add it to the solution in step (4) and sonicate for 30 min, stir and disperse for 30 min, and heat in an oil bath to 80 °C for 3 h.

[0039] (6) After cooling to room temperature, the precipitate was washed repeatedly by centrifugation with water and then with anhydrous ethanol. It was then dried in a vacuum drying oven at 60°C to obtain a yellowish-gray powder. The EDX test results are shown in Table 1. Zn+In+S=1.74%+5.41%+2.89%=10%, indicating that the percentage of ZnIn2S4 in the ZnIn2S4 / Nb2O5 composite photocatalyst is 10%. Therefore, the product obtained in this example is labeled as a 10% ZnIn2S4 / Nb2O5 composite photocatalyst with oxygen vacancies.

[0040]

[0041] Example 2

[0042] A method for preparing a catalyst for photocatalytic water splitting to produce hydrogen, comprising the following steps:

[0043] Steps (1)-(4) are the same as in Example 1;

[0044] (5) Weigh 0.043 g of Nb2O5 powder rich in oxygen vacancies obtained in step (3) and add it to the solution in step (4) and sonicate for 30 min, stir and disperse for 30 min, and heat in an oil bath to 80 °C for 3 h.

[0045] (6) After cooling to room temperature, the precipitate was washed repeatedly by centrifugation with water and then with anhydrous ethanol. It was then dried in a vacuum drying oven at 60 °C to obtain a yellowish-gray powder, which was labeled as a 30% ZnIn2S4 / Nb2O5 composite photocatalyst containing oxygen vacancies.

[0046] Example 3

[0047] A method for preparing a catalyst for photocatalytic water splitting to produce hydrogen, comprising the following steps:

[0048] Steps (1)-(4) are the same as in Example 1;

[0049] (5) Weigh 0.071 g of Nb2O5 powder rich in oxygen vacancies obtained in step (3) and add it to the solution in step (4) and sonicate for 30 min, stir and disperse for 30 min, and heat in an oil bath to 80 °C for 3 h.

[0050] (6) After cooling to room temperature, the precipitate was washed repeatedly by centrifugation with water and then with anhydrous ethanol. It was then dried in a vacuum drying oven at 60 °C to obtain a yellowish-gray powder, which was labeled as a 50% ZnIn2S4 / Nb2O5 composite photocatalyst containing oxygen vacancies.

[0051] Example 4

[0052] A method for preparing a catalyst for photocatalytic water splitting to produce hydrogen, comprising the following steps:

[0053] Steps (1)-(4) are the same as in Example 1;

[0054] (5) Weigh 0.100 g of Nb2O5 powder rich in oxygen vacancies obtained in step (3) and add it to the solution in step (4) and sonicate for 30 min, stir and disperse for 30 min, and heat in an oil bath to 80 °C for 3 h.

[0055] (6) After cooling to room temperature, the precipitate was washed repeatedly by centrifugation with water and then with anhydrous ethanol. It was then dried in a vacuum drying oven at 60 °C to obtain a yellowish-gray powder. The EDX test results are shown in Table 2. The percentage of Zn+In+S is approximately 70%, which indicates that ZnIn2S4 accounts for 70% of the ZnIn2S4 / Nb2O5 composite photocatalyst. Therefore, the product obtained in this example is labeled as a 70% ZnIn2S4 / Nb2O5 composite photocatalyst with oxygen vacancies.

[0056]

[0057] Example 5

[0058] A method for preparing a catalyst for photocatalytic water splitting to produce hydrogen, comprising the following steps:

[0059] Steps (1)-(4) are the same as in Example 1;

[0060] (5) Weigh 0.129 g of Nb2O5 powder rich in oxygen vacancies obtained in step (3) and add it to the solution in step (4) and sonicate for 30 min, stir and disperse for 30 min, and heat in an oil bath to 80 °C for 3 h.

[0061] (6) After cooling to room temperature, the precipitate was washed multiple times by centrifugation with water and then with anhydrous ethanol. It was then dried in a vacuum drying oven at 60 °C to obtain a yellowish-gray powder, which was labeled as a 90% ZnIn2S4 / Nb2O5 composite photocatalyst containing oxygen vacancies.

[0062] Compare with Example 1

[0063] A method for preparing a catalyst for photocatalytic water splitting to produce hydrogen, comprising the following steps:

[0064] (1) Weigh 0.540 g of InCl3·4H2O, 0.136 g of ZnCl2 and 0.300 g of TAA (thioacetamide) and place them in a single-necked flask. Add 80 mL of hydrochloric acid aqueous solution (pH 2.5) and stir to dissolve. Then add 20 mL of glycerol and stir evenly. Heat the mixture in an oil bath to 80 °C and react for 3 h.

[0065] (2) After cooling to room temperature, the precipitate is washed repeatedly by centrifugation with water and then with anhydrous ethanol. It is then dried in a vacuum drying oven at 60 °C. The resulting powder is the ZnIn2S4 photocatalyst.

[0066] Product characterization

[0067] Figure 1 These are scanning electron microscope (SEM) images of Nb2O5 prepared in step (2) of Example 1; from Figure 1 As can be seen, the prepared Nb2O5 has the morphology of a nanoplate with a thickness of about 200 nm.

[0068] Figure 2 This is a scanning electron microscope (SEM) image of the 70% ZnIn2S4 / Nb2O5 composite photocatalyst with oxygen vacancies prepared in Example 4. Figure 3 This is a transmission electron microscope (TEM) image of the 70% ZnIn2S4 / Nb2O5 composite photocatalyst with oxygen vacancies prepared in Example 4. Figure 2 and Figure 3 As can be seen, ZnIn2S4 nanosheets are uniformly grown on the surface of Nb2O5 nanoplatelets, indicating that the two are uniformly composited.

[0069] Figure 4 The image shows the X-ray photoelectron spectroscopy (XPS) of the 70% ZnIn2S4 / Nb2O5 containing oxygen vacancies prepared in Example 4, indicating the presence of Zn, In, S, Nb, and O elements in the sample.

[0070] Figure 5 The X-ray diffraction (XRD) spectra of Nb2O5 prepared in step (2) of Example 4, 70% ZnIn2S4 / Nb2O5 containing oxygen vacancies, and ZnIn2S4 prepared in Control Example 1 are shown. Figure 5 As can be seen, ZnIn2S4 is a hexagonal phase, with JCPDS standard card number 65-2023; Nb2O5 is a hexagonal phase, with JCPDS standard card number 28-0317. From the XRD pattern of 70% ZnIn2S4 / Nb2O5 containing oxygen vacancies, it can be seen that there are peaks of both ZnIn2S4 and Nb2O5, which indicates that the catalyst is a composite photocatalyst of the two.

[0071] Figure 6The electron paramagnetic resonance (EPR) spectra of Nb2O5 prepared in step (2) of Example 4, Nb2O5 rich in oxygen vacancies prepared in step (3) of Example 4, 70% ZnIn2S4 / Nb2O5 containing oxygen vacancies prepared in Example 4, and pure ZnIn2S4 prepared in Control Example 1 are shown; indicating that the Nb2O5 rich in oxygen vacancies and the 70% ZnIn2S4 / Nb2O5 containing oxygen vacancies contain oxygen vacancies.

[0072] Performance testing

[0073] 25 mg of pure Nb2O5 prepared in Examples 1-5 (prepared in step (2)), Nb2O5 rich in oxygen vacancies (prepared in step (3)), 10%, 30%, 50%, 70%, and 90% ZnIn2S4 / Nb2O5 composite photocatalysts, and pure ZnIn2S4 prepared in Control Example 1 were uniformly dispersed in 90 mL of water and 10 mL of triethanolamine solution, respectively. The results were detected by a Labsolar 6A photocatalytic hydrogen production device from Beijing Bofeilai and a Shimadzu 2014C gas chromatograph from Japan.

[0074] Figure 7 This is a graph showing the hydrogen production rates of pure Nb₂O₅ prepared in Examples 1-5, Nb₂O₅ rich in oxygen vacancies, 10-90% ZnIn₂S₄ / Nb₂O₅ composite samples, and pure ZnIn₂S₄ prepared in Control Example 1; from Figure 7 It can be clearly seen that the visible light photocatalytic hydrogen production rates of pure Nb2O5, oxygen-vacancy-rich Nb2O5, 10%, 30%, 50%, 70%, and 90% ZnIn2S4 / Nb2O5 composite photocatalysts, and pure ZnIn2S4 prepared in this invention are 0 mmol·h. -1 ·g -1 0.09 mmol·h -1 ·g -1 0.39 mmol·h -1 ·g -1 0.95 mmol·h -1 ·g -1 2.92 mmol·h -1 ·g -1 3.74 mmol·h -1 ·g -1 2.13 mmol·h -1 ·g -1 0.48 mmol·h -1 ·g -1Clearly, the hydrogen production rate of the 30-90% ZnIn2S4 / Nb2O5 composite sample is significantly higher than that of pure Nb2O5, oxygen-vacancy-rich Nb2O5, and ZnIn2S4, with the 70% ZnIn2S4 / Nb2O5 composite photocatalyst being the best.

[0075] Figure 8 This is a cycle stability test of the 70% ZnIn2S4 / Nb2O5 containing oxygen vacancies prepared in Example 4; from Figure 8 As can be seen, the catalyst of this invention has very stable performance, and its performance did not significantly decrease after 4 cycles (16 hours) of testing.

[0076] In summary, the present invention yields the following important findings:

[0077] (1) The zinc indium sulfide and niobium pentoxide composite photocatalyst rich in oxygen vacancies of the present invention can be used for photocatalytic water splitting to produce hydrogen and has excellent hydrogen production performance.

[0078] (2) All composite samples have visible light response, which breaks through the limitation that Nb2O5 can only utilize ultraviolet light;

[0079] (3) There is an optimal mass percentage of ZnIn2S4 in the catalyst, which is about 70%. If the mass percentage is lower or higher than the optimal value, the photocatalytic hydrogen production effect will not be the best.

[0080] (4) The optimal ratio of 70% ZnIn2S4 / Nb2O5 composite photocatalyst with oxygen vacancies has good cycle stability.

Claims

1. A catalyst for photocatalytic water splitting to produce hydrogen, characterized in that: The catalyst is composed of ZnIn2S4 and Nb2O5 rich in oxygen vacancies, and ZnIn2S4 nanosheets are uniformly grown on the surface of Nb2O5 nanoplates rich in oxygen vacancies. The mass percentage of ZnIn2S4 in the catalyst is controlled between 30% and 90%. The catalyst is prepared in the following steps: (1) Preparation of Nb2O5 nanoplate powder rich in oxygen vacancies: (1.1) Add ammonium niobate oxalate and melamine to ethanol, stir to dissolve, and then vacuum dry to obtain a solid; wherein, the ratio of raw materials is ammonium niobate oxalate: melamine: ethanol = (1.0~3.0) g: (1.5~2.5) g: (15~30) mL; (1.2) The solid obtained in step (1.1) is calcined at 500~700 °C for 4~6 h to obtain Nb2O5 nanoplate powder; (1.3) The Nb2O5 nanoplate powder obtained in step (1.2) is calcined at 500~700 °C for 1~5 h in a nitrogen-hydrogen mixed atmosphere to obtain Nb2O5 nanoplate powder rich in oxygen vacancies. (2) Preparation of the raw material solution for preparing ZnIn2S4 nanosheets: Add water-soluble indium salt, water-soluble zinc salt, and thioacetamide to a hydrochloric acid aqueous solution with pH=2~3, stir to dissolve, then add glycerol and stir until homogeneous; the molar ratio of the raw materials is water-soluble indium salt: water-soluble zinc salt: TAA=2:1:(4~5), and add 70~90 mL of hydrochloric acid aqueous solution and 10~30 mL of glycerol for every 2 mmol of water-soluble indium salt; (3) According to the mass ratio of oxygen-rich Nb2O5 to ZnIn2S4, weigh the oxygen-rich Nb2O5 nanoplate powder obtained in step (1) and add it to the raw material liquid in step (2). After dispersing evenly, react at 80~160 ℃ for more than 3 h. (4) After cooling to room temperature, centrifuge to wash the precipitate, and vacuum dry to obtain the catalyst.

2. The catalyst for photocatalytic water splitting to produce hydrogen as described in claim 1, characterized in that: The mass percentage of ZnIn2S4 in the catalyst is 70%.

3. A method for preparing a catalyst for photocatalytic water splitting to produce hydrogen as described in claim 1 or 2, characterized in that, The steps are as follows: (1) Preparation of Nb2O5 nanoplate powder rich in oxygen vacancies: (1.1) Add ammonium niobate oxalate and melamine to ethanol, stir to dissolve, and then vacuum dry to obtain a solid; wherein, the ratio of raw materials is ammonium niobate oxalate: melamine: ethanol = (1.0~3.0) g: (1.5~2.5) g: (15~30) mL; (1.2) The solid obtained in step (1.1) is calcined at 500~700 °C for 4~6 h to obtain Nb2O5 nanoplate powder; (1.3) The Nb2O5 nanoplate powder obtained in step (1.2) is calcined at 500~700 °C for 1~5 h in a nitrogen-hydrogen mixed atmosphere to obtain Nb2O5 nanoplate powder rich in oxygen vacancies. (2) Preparation of the raw material solution for preparing ZnIn2S4 nanosheets: Add water-soluble indium salt, water-soluble zinc salt, and thioacetamide to a hydrochloric acid aqueous solution with pH=2~3, stir to dissolve, then add glycerol and stir until homogeneous; the molar ratio of the raw materials is water-soluble indium salt: water-soluble zinc salt: TAA=2:1:(4~5), and add 70~90 mL of hydrochloric acid aqueous solution and 10~30 mL of glycerol for every 2 mmol of water-soluble indium salt; (3) According to the mass ratio of oxygen-rich Nb2O5 to ZnIn2S4, weigh the oxygen-rich Nb2O5 nanoplate powder obtained in step (1) and add it to the raw material liquid in step (2). After dispersing evenly, react at 80~160 ℃ for more than 3 h. (4) After cooling to room temperature, centrifuge to wash the precipitate, and vacuum dry to obtain the catalyst.

4. The method for preparing the catalyst for photocatalytic water splitting to produce hydrogen as described in claim 3, characterized in that: In step (1.1), the purity of ethanol is ≥95v.

5. The method for preparing the catalyst for photocatalytic water splitting to produce hydrogen as described in claim 3, characterized in that: In steps (1.2) and (1.3), the calcination heating rate is 0.5~2 ℃·min. -1 .

6. The method for preparing the catalyst for photocatalytic water splitting to produce hydrogen as described in claim 3, characterized in that: In step (3), the mixture is first sonicated and then stirred until it is evenly dispersed.

7. The method for preparing the catalyst for photocatalytic water splitting to produce hydrogen as described in claim 3, characterized in that: In step (4), the water is first used and then ethanol is used for centrifugation and washing.

8. The method for preparing the catalyst for photocatalytic water splitting to produce hydrogen as described in claim 3, characterized in that: In step (4), the temperature for vacuum drying is 60~120 ℃.

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