Preparation of narcissus-shaped zinc cadmium sulfide solid solution photocatalyst

Abstract

The invention relates to preparation and application of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst in the field of photocatalytic hydrogen evolution. The invention aims to provide the narcissus-shaped zinc cadmium sulfide solid solution photocatalyst which is simple and convenient in preparation process and low in cost and has efficient photocatalytic hydrogen evolution performance, so that the photocatalytic hydrogen evolution efficiency is improved, and the urgent demand on clean energy under the current energy crisis is relieved. According to the adopted method, zinc acetate, cadmium chloride, thiourea and polyvinylpyrrolidone serve as raw materials, a one-step hydrothermal synthesis method is adopted, and the prepared narcissus-shaped zinc cadmium sulfide solid solution can be suitable for the field of photocatalytic hydrogen evolution and has high catalytic activity and stability.

Description

Technical Field

[0001] The present invention relates to the field of photocatalytic hydrogen evolution. Background Art

[0002] The solar-driven water splitting reaction, as a frontier approach to achieve sustainable hydrogen energy production, occupies a crucial position in the current energy research field. In this process, photocatalysts play a core role, and their performance parameters, including light absorption efficiency, carrier migration characteristics, and catalytic active sites, have a decisive impact on the energy conversion efficiency and economic cost in the photocatalytic hydrogen evolution process. To achieve efficient and low-cost conversion of solar energy to hydrogen energy, scientific researchers are committed to developing material systems with excellent photocatalytic performance, which need to have the ability to efficiently capture solar photons and convert their energy into chemical energy to drive the water splitting reaction. Therefore, the design and synthesis of high-performance photocatalysts constitute the key scientific issue in the development of solar photocatalytic water splitting technology.

[0003] As a class of inorganic semiconductor materials, cadmium zinc sulfide solid solution has shown broad application prospects in the field of photocatalysis and received extensive attention due to its suitable band gap structure matching the solar spectrum and relatively high light absorption coefficient. However, in practical applications, cadmium zinc sulfide solid solution exposes a series of key problems that need to be solved urgently. First, its spectral response range in the visible light band is relatively narrow, resulting in low utilization efficiency of the visible light energy in solar radiation and unable to fully explore the potential of solar energy resources. Second, the separation efficiency of photo-generated carriers inside and on the surface of cadmium zinc sulfide is not ideal, and a large number of photo-generated electron-hole pairs recombine before participating in the water splitting reaction, seriously restricting the photocatalytic reaction kinetics process and reducing the photocatalytic hydrogen production efficiency. Summary of the Invention

[0004] To overcome the problems such as low utilization efficiency of visible light energy and unsatisfactory separation efficiency of photo-generated carriers in cadmium zinc sulfide solid solution mentioned above, the present invention provides a preparation method of a daffodil-shaped cadmium zinc sulfide solid solution photocatalyst.

[0005] The object of the present invention is achieved as follows:

[0006] A preparation method of a daffodil-shaped cadmium zinc sulfide solid solution photocatalyst, the preparation method comprising the following steps:

[0007] (1) Weigh 0.22 g of zinc acetate, 0.91 g of cadmium chloride, 0.38 g of thiourea, and 0.45 g of polyvinylpyrrolidone, add them together to 36 mL of deionized water, and continuously stir at a stable stirring speed for 15 minutes at room temperature to fully dissolve and mix the raw materials evenly to form a homogeneous reaction solution;

[0008] (2) Ultrasonically treat the above-mentioned well-stirred solution for 20 minutes to further promote the dispersion and mixing between molecules and enhance the uniformity of the reaction system. After the ultrasonic treatment is completed, divide the solution into three equal parts and transfer them to three 20 mL reaction vessels respectively to ensure that the amount of reactants in each reaction vessel is the same;

[0009] (3) Place the reaction vessel containing the reaction solution into a forced-air drying oven set at 220 °C and maintain this temperature for 24 hours to allow the reaction to proceed fully. After the reaction is completed, let the sample cool naturally to room temperature to avoid the influence of sudden temperature changes on the product structure;

[0010] (4) Wash the cooled sample three times with deionized water and anhydrous ethanol respectively to remove the impurities and unreacted raw materials that may remain on the surface of the sample. After the washing is completed, collect the precipitate by centrifugation. Finally, obtain an orange-yellow precipitate product. Place this precipitate product in a forced-air drying oven at 60 °C and dry it for 24 hours to remove the moisture in it, and finally obtain a zinc cadmium sulfide solid solution photocatalyst material with a specific composition.

[0011] The above application method is as follows: Take 5 mg of zinc cadmium sulfide and add it to 20 mL of deionized water containing a mixture of 0.25 mol of sodium sulfite and 0.35 mol of sodium sulfide. After ultrasonic treatment to form a homogeneous suspension, transfer it to a 30 mL reactor. Immediately, use a vacuum pump to evacuate the air in the reactor, and at the same time turn on the cooling water and stirrer. Check and ensure that the airtightness of the device is good. Place a 500 W xenon lamp equipped with a cut-off filter on the side of the reactor and start the light irradiation experiment. During the experiment, take 200 μL of gas from the reactor every 1 hour, inject it into a GC9800 type gas chromatograph to measure the hydrogen content and record it. The results show that the hydrogen production rate of this narcissus-shaped zinc cadmium sulfide solid solution photocatalyst can reach 8.52 mmol g -1 h -1 Moreover, a continuous cycle test of 30 hours for a total of 5 times was carried out on this catalyst. During the 5 cycles, the catalyst showed good stability, and its photocatalytic hydrogen production performance did not show obvious attenuation after the cycle test, providing a strong stability guarantee for its practical application.

[0012] Compared with the prior art, the present invention has the following characteristics:

[0013] The one-step hydrothermal method of the present invention greatly simplifies the preparation process. All reactions are completed in the same reaction kettle, reducing the impurities that may be introduced in the intermediate links. By precisely adjusting reaction conditions such as the molar ratio of zinc ions to cadmium ions, reaction temperature, reaction time, and the added mass of polyvinylpyrrolidone, a cadmium zinc sulfide solid solution with a specific morphology and composition can be prepared targeted, achieving a high degree of preparation controllability. In terms of material properties, the single materials of zinc sulfide and cadmium sulfide prepared by the prior art have many limitations in photocatalytic performance, such as serious recombination of photo-generated carriers and unsatisfactory band gaps. The cadmium zinc sulfide solid solution prepared by the present invention has achieved breakthroughs in multiple key performance indicators by virtue of its unique daffodil morphology and the synergistic effect between zinc ions and cadmium ions. The solid ultraviolet-visible diffuse reflection spectrum shows that its maximum absorption edge is located at 600 nm, which can enhance the absorption ability of photon energy; the photoluminescence spectrum indicates that cadmium zinc sulfide has a lower fluorescence intensity compared to zinc sulfide and cadmium sulfide, enabling the photo-generated electrons to migrate more rapidly and promoting the effective separation of photo-generated electrons and holes; the photocurrent response test shows that cadmium zinc sulfide has a higher transient photocurrent intensity compared to zinc sulfide and cadmium sulfide, which endows it with the ability to inhibit the recombination of photo-generated electrons and holes and improves the separation efficiency of photo-generated electron-hole pairs. The cadmium zinc sulfide solid solution of the present invention exhibits a specific surface area of 3.16 m 2 g -1 due to its daffodil morphology. The larger specific surface area can accelerate the adsorption of reactants and improve the reaction rate. The hydrogen production rate under visible light reaches 8.52 mmol g -1 h -1 . Moreover, in multiple cyclic tests, the catalyst can still maintain good structural stability and catalytic activity. A daffodil-shaped cadmium zinc sulfide solid solution photocatalyst of the present invention is applied to the field of photocatalytic water splitting for hydrogen production. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is the X-ray diffraction pattern of a daffodil-shaped cadmium zinc sulfide solid solution photocatalyst prepared in Example 1 of the present invention.

[0015] Figure 2 is the scanning electron microscope image of a daffodil-shaped cadmium zinc sulfide solid solution photocatalyst prepared in Example 1 of the present invention.

[0016] Figure 3 is the nitrogen adsorption and desorption isotherm of a daffodil-shaped cadmium zinc sulfide solid solution photocatalyst prepared in Example 1 of the present invention.

[0017] Figure 4 is the comparison chart of solid ultraviolet-visible diffuse reflection between a daffodil-shaped cadmium zinc sulfide solid solution photocatalyst prepared in Example 1 of the present invention and cadmium sulfide and zinc sulfide.

[0018] Figure 5 Flat band potential diagram of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention.

[0019] Figure 6 Photoluminescence comparison diagram of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention with cadmium sulfide and zinc sulfide.

[0020] Figure 7 Photocurrent response comparison diagram of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention with cadmium sulfide and zinc sulfide.

[0021] Figure 8 Hydrogen production rate comparison diagram of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention at different reaction times, different reaction temperatures and different addition amounts of polyvinylpyrrolidone.

[0022] Figure 9 Hydrogen production cycle test and X-ray diffraction diagram before and after the cycle test of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention.

[0023] Figure 10 Preparation flow chart of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention. Detailed implementation mode

[0024] The present invention will be described in detail below with reference to the drawings and embodiments.

[0025] Example 1, Application of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst, including the following preparation steps:

[0026] (1) Weigh 0.22 g of zinc acetate, 0.91 g of cadmium chloride, 0.38 g of thiourea and 0.45 g of polyvinylpyrrolidone, add them together to 36 mL of deionized water, and continuously stir at a stable stirring speed for 15 minutes at room temperature to fully dissolve and mix the raw materials evenly to form a homogeneous reaction solution.

[0027] (2) Ultrasonically treat the above-mentioned fully stirred solution, set the ultrasonic time to 20 minutes to further promote the dispersion and mixing between molecules and enhance the uniformity of the reaction system. After the ultrasonic treatment is completed, divide the solution into three equal parts and transfer them to three 20 mL reaction kettles respectively to ensure that the amount of reactants in each reaction kettle is the same.

[0028] (3) Place the reaction kettle containing the reaction solution into a forced-air drying oven set at 220 °C, maintain this temperature for 24 hours to allow the reaction to proceed fully. After the reaction is completed, let the sample cool naturally to room temperature to avoid the impact of sudden temperature changes on the product structure.

[0029] (4) Wash the cooled sample three times with deionized water and anhydrous ethanol respectively to remove the impurities and unreacted raw materials that may remain on the surface of the sample. After the washing is completed, collect the precipitate by centrifugation operation. Finally, an orange-yellow precipitate product is obtained. Place this precipitate product in a forced-air drying oven at 60 °C and dry it for 24 hours to remove the moisture in it, and finally obtain a zinc cadmium sulfide solid solution photocatalyst material with a specific composition.

[0030] The following further describes the present invention in conjunction with the drawings and embodiments: Description of the Drawings

[0032] (I) Conduct X-ray diffraction testing on a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention. We compared it with the standard diffraction pattern and determined that the molecular formula of the zinc cadmium sulfide solid solution composition is Zn 0.2 Cd 0.8 S (PDF#00-040-0835). The diffraction peaks at 2θ of 25.2°, 26.9°, 28.6°, 37.0°, 44.4°, 48.6° and 51.8° correspond to the (100), (002), (101), (102), (110), (103) and (200) crystal planes of zinc cadmium sulfide.

[0033] Figure 1 It is the X-ray diffraction pattern of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention.

[0034] (II) Conduct scanning electron microscopy testing on a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention. It can be seen that the zinc cadmium sulfide solid solution presents a unique narcissus morphology.

[0035] Figure 2 It is the scanning electron microscopy image of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention.

[0036] (3) The nitrogen adsorption - desorption test was carried out on a narcissus - shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention. It can be seen that as the relative pressure increases, the nitrogen adsorption - desorption curve is convex downward in the whole pressure range. Such curves can be classified as typical type III isotherms, showing pore filling. In the range of relative pressure from 0.9 to 1.0, the curve rises significantly, which reflects the existence of mesoporous structure in zinc cadmium sulfide, and its specific surface area is 3.16 m 2 g -1 。

[0037] Figure 3 Nitrogen adsorption - desorption of a narcissus - shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention.

[0038] (4) The solid - state ultraviolet - visible diffuse reflectance tests were carried out on a narcissus - shaped zinc cadmium sulfide solid solution photocatalyst, cadmium sulfide and zinc sulfide prepared in Example 1 of the present invention. It can be seen that zinc sulfide has strong absorption characteristics in the ultraviolet region, while cadmium sulfide and zinc cadmium sulfide not only show strong absorption in the ultraviolet region, but also have certain absorption ability in the visible light region. Among them, the maximum absorption edge of zinc cadmium sulfide is located at 600 nm.

[0039] Figure 4 Solid - state ultraviolet - visible diffuse reflectance comparison chart of a narcissus - shaped zinc cadmium sulfide solid solution photocatalyst, cadmium sulfide and zinc sulfide prepared in Example 1 of the present invention.

[0040] (5) The flat - band potential of a narcissus - shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention was measured. The flat - band potential of zinc cadmium sulfide was tested at frequencies of 1000, 2000 and 3000 Hz respectively. The impedance - potential spectra at each frequency intersect at one point. Its flat - band potential is - 0.68 V relative to the silver / silver chloride electrode, and the tangent slope is positive, belonging to n - type semiconductors.

[0041] Figure 5 Flat - band potential diagram of a narcissus - shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention.

[0042] (6) The photoluminescence tests were carried out on a narcissus - shaped zinc cadmium sulfide solid solution photocatalyst, cadmium sulfide and zinc sulfide prepared in Example 1 of the present invention. It can be seen that zinc sulfide, cadmium sulfide and zinc cadmium sulfide all show high - peak fluorescence intensity at 430 nm. Among them, the fluorescence intensity of zinc cadmium sulfide is the lowest, indicating that its photo - generated electrons can be effectively migrated, promoting the separation of photo - generated electron - hole pairs.

[0043] Figure 6 Photoluminescence comparison chart of a narcissus - shaped zinc cadmium sulfide solid solution photocatalyst, cadmium sulfide and zinc sulfide prepared in Example 1 of the present invention.

[0044] (7) Photocurrent response tests were conducted on a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention, cadmium sulfide, and zinc sulfide. It can be observed that at the same light intensity, zinc sulfide and cadmium sulfide exhibit lower photocurrent intensities, while the transient photocurrent intensity of zinc cadmium sulfide is significantly enhanced, indicating that the synergistic effect between zinc ions and cadmium ions can effectively improve the charge transfer ability of the catalyst and accelerate the charge migration rate.

[0045] Figure 7 It is a comparative diagram of photocurrent responses of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention, cadmium sulfide, and zinc sulfide.

[0046] (8) Regarding the hydrogen production rate of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention at different reaction times, different reaction temperatures, and different addition amounts of polyvinylpyrrolidone, it is found that when the reaction temperature is 220 °C, the reaction time is 24 hours, and the added mass of polyvinylpyrrolidone is 0.45 g, the hydrogen production rate of zinc cadmium sulfide is the highest, which is 8.52 mmol g -1 h -1 。

[0047] Figure 8 It is a comparative diagram of the hydrogen production rates of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention at different reaction times, different reaction temperatures, and different addition amounts of polyvinylpyrrolidone.

[0048] (9) Hydrogen production cycle tests and X-ray diffraction tests before and after the cycle tests were conducted on a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention. The results show that the zinc cadmium sulfide solid solution photocatalyst exhibits good stability and catalytic activity in 5 consecutive cycle tests with a duration of 30 hours.

[0049] Figure 9 It is an X-ray diffraction pattern of the hydrogen production cycle test of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention and before and after the cycle test.

[0050] (10) Regarding the preparation process of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention, the raw materials are zinc acetate, cadmium chloride, thiourea, and polyvinylpyrrolidone, and the hydrothermal synthesis method is adopted.

[0051] Figure 10 It is a preparation flow chart of a narcissus-shaped zinc cadmium sulfide solid solution photocatalyst prepared in Example 1 of the present invention.

[0052] In summary, in this embodiment, by using the one-step hydrothermal method and taking zinc acetate, cadmium chloride, thiourea, and polyvinylpyrrolidone as reaction raw materials, a zinc cadmium sulfide solid solution photocatalyst with a daffodil shape is successfully prepared, and this catalyst has good catalytic activity and structural stability.

Claims

1. A preparation method of a daffodil-shaped zinc cadmium sulfide solid solution photocatalyst, the preparation method comprising the following steps: (1) Weigh 0.22 g of zinc acetate, 0.91 g of cadmium chloride, 0.38 g of thiourea and 0.45 g of polyvinyl pyrrolidone, add them together into 36 mL of deionized water, and stir at room temperature for 15 minutes at a stable stirring speed to fully dissolve and mix the raw materials to form a uniform reaction solution; (2) The stirred solution was ultrasonically treated for 20 minutes to further promote the dispersion and mixing of molecules and enhance the uniformity of the reaction system. After the ultrasonic treatment, the solution was divided into three parts and transferred to three 20 mL reactors respectively to ensure that the amount of reactants in each reactor was consistent. (3) The reaction kettle containing the reaction solution was placed in a blast drying oven set at 220° C. and maintained at this temperature for 24 hours to allow the reaction to proceed fully. After the reaction was completed, the sample was allowed to cool naturally to room temperature to avoid the influence of sudden temperature changes on the product structure; (4) The cooled sample was washed three times with deionized water and anhydrous ethanol respectively to remove impurities and unreacted raw materials that may remain on the surface of the sample. After washing, the precipitate was collected by centrifugation to finally obtain an orange-yellow precipitate product. The precipitate product was placed in a forced air drying oven at a temperature of 60°C and dried for 24 hours to remove the moisture therein, and finally a zinc cadmium sulfide solid solution photocatalyst material with a specific composition was obtained.

2. Application of a daffodil-shaped zinc cadmium sulfide solid solution photocatalyst prepared by the preparation method of claim 1, characterized in that: A daffodil-shaped zinc cadmium sulfide solid solution photocatalyst is used in the field of photocatalytic water hydrogen production.

3. The preparation of a daffodil-shaped zinc cadmium sulfide solid solution photocatalyst according to claim 1, characterized in that Weigh 0.22 g of zinc acetate, 0.91 g of cadmium chloride, 0.38 g of thiourea and 0.45 g of polyvinyl pyrrolidone as described in step 1.

4. The preparation of a daffodil-shaped zinc cadmium sulfide solid solution photocatalyst according to claim 1, characterized in that The sonication time described in step 2 was set to 20 min.

5. The preparation of a daffodil-shaped zinc cadmium sulfide solid solution photocatalyst according to claim 1, characterized in that The setting temperature of the blast drying oven described in step 3 is 220°C.

6. The preparation of a daffodil-shaped zinc cadmium sulfide solid solution photocatalyst according to claim 1, characterized in that The obtained product was dried in a forced air drying oven at 60° C. for 24 hours as described in step 4.

7. The use of a daffodil-shaped zinc cadmium sulfide solid solution photocatalyst according to claim 1, characterized in that: The application method is as follows: take 5 mg of cadmium zinc sulfide, add it to 20 mL of deionized water containing 0.25 mol of sodium sulfite and 0.35 mol of sodium sulfide, after ultrasonic treatment, form a uniform suspension, transfer it to a 30 mL reactor, then use a vacuum pump to exhaust the air in the reactor, turn on the cooling water and stirrer at the same time, check and ensure that the device is airtight, place a 500W xenon lamp equipped with a cutoff filter on the side of the reactor, and start the illumination experiment. During the experiment, 200 μL of gas is extracted from the reactor every 1 hour, injected into the GC9800 gas chromatograph to determine the hydrogen content and record it. The results show that the hydrogen production rate of the daffodil-shaped cadmium zinc sulfide solid solution photocatalyst can reach 8.52 mmol g -1 h -1 In addition, the catalyst was subjected to a continuous cycle test for 30 hours and a total of 5 times. During the 5 cycles, the catalyst showed good stability, and its photocatalytic hydrogen production performance did not show obvious attenuation after the cycle test, providing a strong stability guarantee for its practical application.

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