Concentric nanosheets, methods of making and using the same

Abstract

The application discloses concentric circle nanosheets and a preparation method and application thereof, and the preparation method of the concentric circle nanosheets comprises the following steps: (S1) mixing sodium citrate, cadmium chloride and zinc chloride in water to obtain a flocculent solution; (S2) adding ammonia water and thiourea into the flocculent solution in the step (S1) and heating to react, so that the concentric circle nanosheet is prepared. 1‑x Zn x The application firstly prepares Cd 1‑x Zn x S@CdCN2 concentric circle nanosheet, then Cd 1‑ x Zn x S@CdS concentric circle nanosheet and Cd 1‑x Zn x S@CdS-Ni(OH)2 concentric circle composite nanosheet are prepared through in-situ sulfuration and photodeposition methods respectively. In the concentric circle composite nanosheet, CdCN2 is converted into CdS through a sulfuration reaction, and Ni(OH)2 is deposited on the Cd 1‑x Zn x S central particle through a photodeposition reaction.

Description

Technical Field

[0001] This invention belongs to the field of inorganic nanocomposite material preparation technology and photocatalysis, specifically relating to a concentric nanosheet, its preparation method, and its application in photocatalytic water splitting for hydrogen production. In particular, it relates to a Cd... 1-x Zn x S@CdCN2、Cd 1-x Zn x S@CdS and Cd 1-x Zn x S@CdS-Ni(OH)2 concentric nanosheets, their preparation method, and their application in photocatalytic water splitting for hydrogen production. Background Technology

[0002] With rapid socio-economic development, environmental pollution and energy shortages are becoming increasingly serious problems, making the search for an environmentally friendly and sustainable energy source imperative. Hydrogen is widely recognized as the cleanest renewable energy source, possessing advantages such as high calorific value, wide availability, and ease of storage and transportation. Among various methods of hydrogen production, semiconductor photocatalytic water splitting technology utilizing renewable solar energy has shown broad application prospects. To improve the efficiency of hydrogen production through water splitting, designing and developing stable, efficient, and low-cost photocatalysts is crucial.

[0003] Among various semiconductor materials, cadmium sulfide (CdS) has a relatively narrow bandgap (around 2.4 eV), and its conduction band edge potential is higher than that of H. + The reduction potential of CdS / H2 is more negative; therefore, cadmium sulfide has been widely used in photocatalytic water splitting for hydrogen production under visible light irradiation. However, the high photogenerated charge recombination rate and photocorrosion of pure CdS significantly weaken the activity and stability of photocatalytic water splitting for hydrogen production. Studies have found that, compared to pure CdS, Zn-doped CdS... 1-x Zn x S solid solutions can optimize the electronic band structure of CdS, improving its stability and the reducibility of photogenerated electrons while maintaining strong visible light response. Furthermore, considering the structural advantages of two-dimensional semiconductors, such as significantly shortened carrier migration distance from the bulk phase to the surface, higher specific surface area, and more catalytically active sites, designs based on CdS are also possible. 1-x Zn x Two-dimensional nanomaterials containing S solid solutions hold promise for efficient photocatalytic water splitting to produce hydrogen. However, both the zincblende and wurtzite phases in CdS crystals are non-layered, which makes Cd... 1-x Zn x The synthesis of Cd solid solution two-dimensional nanomaterials is very challenging. Therefore, how to controllably prepare Cd-based... 1-x Zn x Two-dimensional photocatalytic materials based on S solid solutions have become one of the most pressing problems to be solved. Summary of the Invention

[0004] Among various methods for synthesizing two-dimensional semiconductor structures, chemical transformation via two-dimensional precursors is a promising strategy. This approach not only allows for the design and synthesis of two-dimensional semiconductor materials with various compositions but also enables the manipulation of defects and pore structures. Therefore, the objective of this invention is to provide a two-dimensional precursor for preparing Cd-based semiconductors. 1- x Zn x Concentric nanosheets of CdS solid solution significantly improve the photocatalytic hydrogen production performance of water splitting. Furthermore, research shows that the pn heterojunction formed by Ni(OH)2 and CdS can significantly promote the separation process of photogenerated charges, thereby greatly improving the photocatalytic performance of CdS. Therefore, Ni(OH)2 can be used as a CdS-based... 1-x Zn x S solid solution is an ideal component for highly efficient photocatalytic water splitting to produce hydrogen.

[0005] Based on this, the present invention provides concentric nanosheets, their preparation method, and their application in the field of photocatalytic water splitting for hydrogen production.

[0006] Specifically, the technical solution of the present invention is as follows:

[0007] A method for preparing concentric nanosheets, the method comprising the following steps:

[0008] (S1) Sodium citrate, cadmium chloride, and zinc chloride are mixed in water to obtain a flocculent solution;

[0009] (S2) Add ammonia and thiourea to the flocculent solution from step (S1), heat and react to prepare concentric nanosheets.

[0010] According to the present invention, in step (S2), the concentric nanosheets are Cd 1-x Zn x S@CdCN2 concentric nanosheets, wherein 0.05≤x≤0.50, preferably 0.05≤x≤0.25.

[0011] According to the present invention, the method further includes step (S3): mixing and reacting the concentric nanosheets from step (S2) with Na2S and Na2SO3 to prepare modified concentric nanosheets.

[0012] According to the present invention, in step (S3), the modified concentric nanosheets are Cd 1-x Zn x S@CdS concentric nanosheets.

[0013] According to the present invention, the method further includes step (S4): mixing and reacting the concentric nanosheets from step (S2) with Na2S, Na2SO3 and Ni(NO3)2, and preparing concentric composite nanosheets under visible light irradiation.

[0014] According to the present invention, in step (S4), the concentric circular composite nanosheets are Cd 1-x Zn x S@CdS-Ni(OH)2 concentric nanosheets.

[0015] According to the present invention, step (S1) specifically involves first dispersing sodium citrate in water to obtain a colorless and transparent solution, then dissolving cadmium chloride and zinc chloride in water, and adding the resulting solution to the colorless and transparent solution to prepare a colorless and transparent flocculent solution.

[0016] According to the present invention, in step (S1), the mass ratio of sodium citrate, cadmium chloride, and zinc chloride is 1:(0.233-0.443):(0.014-0.139).

[0017] According to the present invention, in step (S1), the concentration of sodium citrate in water is 0.01-0.04 g / mL.

[0018] According to the present invention, in step (S2), the volume ratio of ammonia to thiourea is 1:(7-12), preferably 1:(9-11). Preferably, thiourea is added in the form of an aqueous thiourea solution, wherein the concentration of the aqueous thiourea solution is 0.6-1.0M.

[0019] According to the present invention, in step (S2), the reaction temperature is 30-80°C, preferably 40-70°C, and the reaction time is 2-5 hours, preferably 3-4 hours.

[0020] According to the present invention, step (S2) further includes a post-processing step: allowing the prepared product to stand, taking the supernatant, washing it with ethanol and water, and drying it.

[0021] According to the present invention, in step (S3), the reaction is carried out in water.

[0022] According to the present invention, in step (S3), the concentration of the concentric nanosheets in water is 0.05-0.30 mg / mL, preferably 0.10-0.20 mg / mL.

[0023] According to the present invention, in step (S3), the concentration of Na2S in water is 0.20-0.45M, preferably 0.30-0.40M.

[0024] According to the present invention, in step (S3), the concentration of Na2SO3 in water is 0.10-0.40M, preferably 0.20-0.30M.

[0025] According to the present invention, step (S3) further includes a post-processing step: centrifuging the prepared product, washing it with ethanol and water, and drying it.

[0026] According to the present invention, in step (S4), the reaction is carried out in water.

[0027] According to the present invention, in step (S4), the concentration of the concentric nanosheets in water is 0.05-0.30 mg / mL, preferably 0.10-0.20 mg / mL.

[0028] According to the present invention, in step (S4), the concentration of Na2S in water is 0.20-0.45M, preferably 0.30-0.40M.

[0029] According to the present invention, in step (S4), the concentration of Na2SO3 in water is 0.10-0.40M, preferably 0.20-0.30M.

[0030] According to the present invention, in step (S4), the mass ratio of the concentric nanosheets to Ni(NO3)2 is 1:(0.02-0.35), preferably 1:(0.10-0.25).

[0031] According to the present invention, in step (S4), the wavelength of visible light is greater than 400 nm, preferably 400-500 nm; the illumination time is 0.2-3.0 h, preferably 0.5-1.0 h. For example, a xenon lamp is used as the light source, and preferably, the power of the xenon lamp is 300 W.

[0032] According to the present invention, step (S4) further includes a post-processing step: centrifuging the prepared product, taking the precipitate, washing it with ethanol and water, and drying it.

[0033] As an exemplary embodiment of the present invention, the method for preparing the concentric nanosheets includes the following steps:

[0034] (1) Disperse 1.47g of sodium citrate in 50mL of water and stir magnetically until fully dissolved to obtain a colorless and transparent solution;

[0035] (2) Weigh 0.34-0.65g of cadmium chloride and 0.02-0.20g of zinc chloride and dissolve them in 10mL of aqueous solution by ultrasonication. Then pour the solution into the colorless and transparent solution in step (1) and stir magnetically for 15-30 minutes to obtain a colorless and transparent flocculent solution.

[0036] (3) Add 1 mL of ammonia water and 10 mL of 0.9 M thiourea solution dropwise to step (2) in sequence. Then, transfer the well-stirred mixture into a 250 mL round-bottom flask and heat it in an oil bath at 60 °C for 2-5 hours. After standing for 3-5 hours, centrifuge the product in the supernatant and wash it several times with ethanol and deionized water. Dry it in a vacuum oven at 60 °C for 12 hours to obtain concentric nanosheets.

[0037] (4) The concentric nanosheets in step (3) were ultrasonically dispersed in 100 mL of aqueous solution containing Na2S and Na2SO3. After stirring for 30 minutes, the product was washed several times by centrifugation with ethanol and deionized water and dried in a vacuum oven at 60°C for 12 hours to obtain modified concentric nanosheets.

[0038] Alternatively, (5) the concentric nanosheets from step (3) are ultrasonically dispersed in 100 mL of Na2S, Na2SO3 and Ni(NO3)2 aqueous solution, and the resulting suspension is then transferred to a reactor connected to a closed circulation system. The reaction system is evacuated to a high vacuum state using a vacuum pump, and a 300W xenon lamp equipped with a 400nm cutoff filter is used as the light source. The temperature of the reaction is controlled by a constant temperature circulating water pump. After a period of light irradiation under visible light, the precipitate is collected by centrifugation and washed several times with ethanol and deionized water. The precipitate is then dried in a vacuum oven at 60°C for 12 hours to obtain concentric composite nanosheets.

[0039] The present invention also provides a concentric nanosheet prepared by the above method.

[0040] The present invention also provides the application of the above-mentioned concentric nanosheets in the field of photocatalytic water splitting for hydrogen production.

[0041] The beneficial effects of this invention are:

[0042] (1) This invention is the first to prepare Cd 1-x Zn x S@CdCN2 concentric nanosheets were used to prepare Cd nanosheets, which were then prepared by in-situ sulfidation and photodeposition methods, respectively. 1-x Zn x S@CdS concentric nanosheets and Cd 1-x Zn x S@CdS-Ni(OH)2 concentric circular composite nanosheets. In this process, CdCN2 is converted to CdS via a sulfidation reaction, while Ni(OH)2 is deposited onto CdS via photodeposition. 1-x Zn x On the S-center particle.

[0043] (2) The preparation method of the present invention has mild reaction conditions, simple and controllable operation, and low cost, and produces Cd. 1-x Zn xThe hydrogen production rate of S@CdS (x=0.25) can reach up to 34.94 mmol·h. -1 ·g -1 The prepared Cd 0.75 Zn 0.25 The hydrogen production rate of S@CdS-Ni(OH)2 can reach up to 77.66 mmol·h. -1 ·g -1 . Attached Figure Description

[0044] Figure 1 Scanning electron microscope image of CdS@CdCN2 nanosheets prepared in Comparative Example 1;

[0045] Figure 2 Cd prepared by method (a) of Example 1 0.75 Zn 0.25 Scanning electron microscope images of S@CdCN2 concentric nanosheets;

[0046] Figure 3 For the CdS@CdCN2 nanosheets prepared in Comparative Example 1, and the Cd nanosheets prepared by method (a) in Example 1, 0.75 Zn 0.25 XRD patterns of S@CdCN2 concentric nanosheets and CdCN2 nanosheets prepared in Comparative Example 2;

[0047] Figure 4 Cd prepared by method (b) of Example 1 0.75 Zn 0.25 S@CdS and Cd prepared by method (c) in Example 1 0.75 Zn 0.25 Photocatalytic hydrogen production activity of S@CdS-5%Ni(OH)2 in Na2S / Na2SO3 solution. Detailed Implementation

[0048] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0049] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0050] Example 1

[0051] (a)Cd 0.75 Zn 0.25 Preparation of S@CdCN2 concentric nanosheets

[0052] (1) Add 1.47g sodium citrate to 50mL of water and stir magnetically to dissolve it to obtain a colorless and transparent solution;

[0053] (2) Weigh 0.51g CdCl2 and 0.1g ZnCl2 and dissolve them in 10mL of water by sonication. Then pour them into the solution in step (1) and stir magnetically for 20 minutes to obtain a colorless and transparent flocculent solution.

[0054] (3) Add 1 mL of ammonia water and 10 mL of 0.9 M thiourea aqueous solution dropwise to the solution obtained in step (2), then transfer the mixed solution to a 250 mL round-bottom flask, heat in an oil bath at 60 °C for 3 hours, let stand for 3-5 hours, finally centrifuge the product in the supernatant and wash it several times with ethanol and deionized water, and dry it in a vacuum oven at 60 °C for 12 hours to obtain Cd. 0.75 Zn 0.25 S@CdCN2 concentric nanosheets.

[0055] like Figure 2 As shown, this is the Cd prepared in Example 1. 0.75 Zn 0.25 Scanning electron microscope (SEM) images of S@CdCN2 concentric nanosheets show that they have a concentric nanosheet morphology.

[0056] like Figure 3 As shown, Cd prepared by method (a) in Example 1 0.75 Zn 0.25 The XRD diffraction peaks of S@CdCN2 are consistent with those of wurtzite phase CdS (JCPDS No. 80-0006) and hexagonal phase CdCN2 (JCPDS No. 36-0657), indicating that Cd 0.75 Zn 0.25 S@CdCN2 is composed of wurtzite CdS and hexagonal CdCN2. (b)Cd 0.75 Zn 0.25 Preparation of S@CdS concentric nanosheets

[0057] 10mg of Cd 0.75 Zn 0.25 S@CdCN2 nanosheets were ultrasonically dispersed in 100 mL of an aqueous solution containing 0.35 M Na2S and 0.25 M Na2SO3. After stirring at room temperature for 30 minutes, the product was centrifuged and washed several times with ethanol and deionized water. The product was then dried in a vacuum oven at 60 °C for 12 hours to obtain Cd22 nanosheets. 0.75 Zn 0.25 S@CdS concentric nanosheets.

[0058] (c)Cd 0.75 Zn 0.25 Preparation of S@CdS-5%Ni(OH)2 concentric nanosheets

[0059] Weigh 10 mg of Cd prepared in method (a) of Example 1. 0.75 Zn 0.25 S@CdCN2 was ultrasonically dispersed in 100 mL of an aqueous solution containing 1.7 mg Ni(NO3)2, 0.35 M Na2S, and 0.25 M Na2SO3. The suspension was then transferred to a reactor connected to a closed-loop system. The reaction system was evacuated to a high vacuum using a vacuum pump. A 300 W xenon lamp equipped with a 400 nm cutoff filter was used as the light source. The temperature was controlled at 10 °C by a constant-temperature circulating water pump. After irradiation for 30 minutes, the precipitate was collected by centrifugation and washed several times with ethanol and deionized water. The precipitate was then dried in a vacuum oven at 60 °C for 12 hours to obtain Cd. 0.75 Zn 0.25 S@CdS-5%Ni(OH)2 concentric nanosheets (where 5% represents the mass fraction of Ni(OH)2).

[0060] Comparative Example 1

[0061] Preparation of CdS@CdCN2 nanosheets

[0062] (1) Add 1.47g sodium citrate to 50mL of water and stir magnetically to dissolve it to obtain a colorless and transparent solution;

[0063] (2) Weigh 0.69g CdCl2 and dissolve it in 10mL of water by sonication. Then pour it into the solution in step (1) and stir magnetically for 20 minutes to obtain a colorless and transparent solution.

[0064] (3) Add 1 mL of ammonia water and 10 mL of 0.9 M thiourea aqueous solution dropwise to the solution obtained in step (2). Then, transfer the well-stirred mixture to a 250 mL round-bottom flask and heat it in an oil bath at 60 °C for 3 hours. After standing for 3-5 hours, centrifuge the product in the supernatant and wash it several times with ethanol and deionized water. Dry it in a vacuum oven at 60 °C for 12 hours to obtain CdS@CdCN2 nanosheets.

[0065] like Figure 1 The image shown is a scanning electron microscope image of the CdS@CdCN2 product prepared in Comparative Example 1, which shows its nanosheet structure and many particles dispersed on the surface of the nanosheets.

[0066] Comparative Example 2

[0067] Preparation of CdCN2 nanosheets

[0068] (1) Follow the method and conditions of step (1) in Comparative Example 1;

[0069] (2) Follow the method and conditions of step (2) in Comparative Example 1;

[0070] (3) Add 1 mL of ammonia and 0.23 mL of cyanamide dropwise to the solution obtained in step (2), then transfer the mixed solution to a 250 mL round-bottom flask, heat in an oil bath at 60 °C for 3 hours, let stand for 3-5 hours, then centrifuge the product and wash it several times with ethanol and deionized water, and dry it in a vacuum oven at 60 °C for 12 hours to obtain CdCN2 nanosheets.

[0071] like Figure 3 As shown, the XRD diffraction peaks of the CdCN2 product prepared in Comparative Example 2 are consistent with those of the hexagonal CdCN2 (JCPDS No. 36-0657).

[0072] Test Example 1

[0073] Cd 0.75 Zn 0.25 Performance Testing of Photocatalytic Water Splitting for Hydrogen Production from S@CdS Concentric Nanosheets

[0074] Weigh 10 mg of Cd prepared in method (a) of Example 1. 0.75 Zn 0.25 S@CdCN2 was ultrasonically dispersed in 100 mL of an aqueous solution containing 0.35 M Na2S and 0.25 M Na2SO3. The suspension was then transferred to a reactor connected to a closed-loop circulation system. The reaction system was evacuated to a high vacuum using a vacuum pump. A 300 W xenon lamp equipped with a 400 nm cutoff filter was used as the light source. A constant-temperature circulating water pump controlled the reaction temperature at 10 °C for 2.5 hours. The generated hydrogen gas was detected by gas chromatography every half hour, and the peak area was recorded.

[0075] Test Example 2

[0076] Cd 0.75 Zn 0.25 Performance Testing of Photocatalytic Water Splitting Hydrogen Production from S@CdS-5%Ni(OH)2 Concentric Nanosheets

[0077] Weigh 10 mg of Cd prepared in method (a) of Example 1. 0.75 Zn 0.25 S@CdCN2 was ultrasonically dispersed in 100 mL of an aqueous solution containing 1.7 mg Ni(NO3)2, 0.35 M Na2S, and 0.25 M Na2SO3. The suspension was then transferred to a reactor connected to a closed-loop circulation system. The reaction system was evacuated to a high vacuum using a vacuum pump. A 300 W xenon lamp equipped with a 400 nm cutoff filter was used as the light source. A constant-temperature circulating water pump controlled the reaction temperature at 10 °C for 2.5 hours. The generated hydrogen gas was detected by gas chromatography every half hour, and the peak area was recorded.

[0078] Figure 4Cd prepared by method (b) of Example 1 0.75 Zn 0.25 S@CdS and Cd prepared by method (c) in Example 1 0.75 Zn 0.25 Photocatalytic hydrogen production activity diagram of S@CdS-5%Ni(OH)2 concentric nanosheets. From Figure 4 Calculations show that Cd 0.75 Zn 0.25 The photocatalytic hydrogen production rate of S@CdS concentric nanosheets through water splitting was 34.94 mmol·h. -1 ·g -1 And Cd 0.75 Zn 0.25 The hydrogen production rate of S@CdS-5%Ni(OH)2 concentric nanosheets was significantly increased to 77.66 mmol·h. -1 ·g -1 This indicates that Cd prepared by photodeposition method 0.75 Zn 0.25 S@CdS-5%Ni(OH)2 can effectively improve the hydrogen production efficiency of photocatalysts.

[0079] The embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing concentric nanosheets, characterized in that, The method includes the following steps: (S1) Sodium citrate, cadmium chloride, and zinc chloride are mixed in water to obtain a flocculent solution; (S2) Add ammonia and thiourea to the flocculent solution in step (S1), heat and react to prepare concentric nanosheets; The method further includes step (S3): mixing and reacting the concentric nanosheets from step (S2) with Na2S and Na2SO3 to prepare modified concentric nanosheets; or, The method further includes step (S4): mixing and reacting the concentric nanosheets from step (S2) with Na2S, Na2SO3 and Ni(NO3)2, and preparing concentric composite nanosheets under visible light irradiation; In step (S1), the mass ratio of sodium citrate, cadmium chloride, and zinc chloride is 1:(0.233-0.443):(0.014-0.139). In step (S1), the concentration of sodium citrate in water is 0.01-0.04 g / mL; In step (S2), the volume ratio of ammonia to thiourea is 1:(7-12); In step (S2), the reaction temperature is 30-80℃ and the reaction time is 2-5h.

2. The method according to claim 1, characterized in that, In step (S2), the concentric nanosheets are Cd 1- x Zn x S@CdCN2 concentric nanosheets, where 0.05≤x≤0.

50.

3. The method according to claim 1, characterized in that, In step (S3), the modified concentric nanosheets are Cd 1-x Zn x S@CdS concentric nanosheets.

4. The method according to claim 1, characterized in that, In step (S4), the concentric circular composite nanosheets are Cd 1-x Zn x S@CdS-Ni(OH)2 concentric nanosheets.

5. The method according to claim 1, characterized in that, In step (S3), the reaction is carried out in water.

6. The method according to claim 5, characterized in that, In step (S3), the concentration of the concentric nanosheets in water is 0.05-0.30 mg / mL.

7. The method according to claim 1, characterized in that, In step (S4), the reaction is carried out in water.

8. The method according to claim 7, characterized in that, In step (S4), the concentration of the concentric nanosheets in water is 0.05-0.30 mg / mL.

9. The method according to claim 1, characterized in that, In step (S4), the wavelength of visible light is greater than 400 nm; the illumination time is 0.2-3.0 h.

10. The concentric nanosheets prepared by the method according to any one of claims 1-9.

11. The application of the concentric nanosheets of claim 10 in the field of photocatalytic water splitting for hydrogen production.

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