Double heterostructure material, and preparation method therefor and use thereof

Abstract

Disclosed in the present application are a double heterostructure material, and a preparation method therefor and the use thereof. The double heterostructure material is a CdS / Bi2S3 / ZnS composite material, wherein spherical Bi2S3 is used as a carrier, and CdS particles and ZnS particles are uniformly dispersed on the surface of Bi2S3, thereby forming a double heterostructure. The preparation method therefor comprises: dissolving Bi(NO3)3•5H2O in an ethylene glycol solution, so as to obtain a solution A; dissolving ZnCl2 in water, so as to obtain a solution B; dissolving CdCl2•2.5H2O in water, so as to obtain a solution C; and mixing the solutions A, B and C, adding L-cysteine to the mixed solution, and subjecting same to a hydrothermal reaction, followed by washing and drying, so as to obtain a CdS / Bi2S3 / ZnS composite material. The double heterostructure material can be used in the photocatalytic reduction of carbon dioxide to selectively reduce carbon dioxide into CH4.

Description

A double heterojunction structure material and its preparation method and application

[0001] Cross-references

[0002] This application claims priority to Chinese patent application No. 202311136362.9, filed on September 5, 2023, entitled “A double heterojunction structure photocatalyst and its preparation method and application,” all disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present application belongs to the technical field of composite materials, and in particular relates to a double heterojunction structure material and a preparation method and application thereof. Background Art

[0004] As the world entered the industrial age, humanity's demand for fossil fuels increased. Excessive use of fossil fuels has led to serious energy crises and environmental pollution. The combustion of fossil fuels emits large amounts of carbon dioxide, the primary greenhouse gas contributing to global warming. To address these energy crises and environmental issues, research has discovered that photocatalytic reduction can convert carbon dioxide into renewable fuels. This not only reduces carbon dioxide emissions but also provides a useful energy source, playing a significant role in alleviating energy crises and addressing environmental pollution.

[0005] Photocatalysis can utilize solar energy as a driving force, effectively reducing energy loss and utilizing photogenerated electrons from photocatalysts to reduce carbon dioxide. However, the rapid electron-hole pair recombination rate of photocatalysts and the low utilization rate of photogenerated electrons limit their widespread application. Metal sulfides, as semiconductor photocatalysts, have been extensively studied in the field of photocatalysis and are currently one of the most promising photocatalytic materials due to their unique electronic properties and light absorption and conversion capabilities. The presence of S 3p orbitals in metal sulfides gives them narrower energy bands and correspondingly smaller hole masses, resulting in a stronger quantum size effect, which facilitates the transfer and separation of photogenerated carriers. However, during the reduction reaction, CO2 combines with electrons to form various reduction products, such as CO and CH4. Although the photocatalytic reduction of CO2 to CH4 is thermodynamically favorable, most photocatalysts struggle to achieve high selectivity for CH4 production, and the selectivity is uncontrollable. This is primarily due to the difficulty in regulating the binding capacity between the reaction intermediates and the material.

[0006] In recent years, researchers have employed various strategies to improve the selectivity of the product CH₄, such as surface modification, ion doping, and metal co-catalysts. However, these common manipulation methods are cumbersome and often require the addition of surface modifiers or expensive metal co-catalysts, making them economically inefficient. Therefore, developing a photocatalyst that selectively reduces CO₂ to CH₄ and an efficient preparation method are of great value.

[0007] Application Contents

[0008] To address the above technical issues, the present application provides a double heterojunction structure material and its preparation method. The photocatalyst uses spherical Bi2S3 as a carrier, with CdS and ZnS particles uniformly dispersed on the Bi2S3 surface, forming a double heterojunction structure and Cd-Zn-Bi ternary metal active sites. This effectively promotes the separation of photogenerated electron-hole pairs, improves the utilization rate of photogenerated charges, and enables the selective reduction of CO2 to CH4.

[0009] The specific application plan is as follows:

[0010] One of the purposes of the present application is to provide a double heterojunction structure material, which is a CdS / Bi2S3 / ZnS composite material, with spherical Bi2S3 as a carrier, and CdS particles and ZnS particles are uniformly dispersed on the Bi2S3 surface to form a double heterojunction structure; the molar ratio of ZnS, Bi2S3, and CdS in the CdS / Bi2S3 / ZnS composite material is 3:1:0.1-5.

[0011] Among them, the diameter of spherical Bi2S3 is 1-3μm, the diameter of CdS particles is 20-100nm, and the diameter of ZnS particles is 20-100nm.

[0012] The molar ratio of ZnS, Bi2S3 and CdS in the CdS / Bi2S3 / ZnS composite material is 3:2:0.9-2.

[0013] The double heterojunction structure material described in this application uses spherical Bi2S3 as a carrier, and CdS particles and ZnS particles are evenly dispersed on the Bi2S3 surface to form a double heterojunction structure, which effectively promotes the separation of photogenerated electron-hole pairs and improves the utilization rate of photogenerated charges; at the same time, due to the interaction between Cd atoms and Zn-Bi atoms, Cd-Zn-Bi ternary metal reaction sites are formed, which can effectively inhibit the reaction intermediate CO2 during the photocatalytic reduction of CO2. * The shedding of CO2 promotes its further hydrogenation to produce CH4, and selectively reduces CO2 to CH4.

[0014] The second object of the present application is to provide a method for preparing the double heterojunction structure material, comprising: dissolving Bi(NO3)3·5H2O in an ethylene glycol solution to obtain solution A; dissolving ZnCl2 in water to obtain solution B; dissolving CdCl2·2.5H2O in water to obtain solution C; mixing solutions A, B, and C, adding L-cysteine ​​to the mixture, subjecting the mixture to a hydrothermal reaction, washing, and drying to obtain a CdS / Bi2S3 / ZnS composite material; the molar ratio of ZnCl2, Bi(NO3)3·5H2O, and CdCl2·2.5H2O in the mixture is 3:2:0.1-5.

[0015] The present application synthesizes the double heterojunction structure material through a one-step hydrothermal method, and forms a special ternary metal reaction active site by regulating the synthesis ratio between metals, thereby effectively improving the selectivity of carbon dioxide reduction products. The preparation method is simple, practical and economical.

[0016] The molar ratio of ZnCl2, Bi(NO3)3·5H2O and CdCl2·2.5H2O in the mixed solution is 3:2:0.9-2.

[0017] The molar ratio of L-cysteine ​​to CdCl2·2.5H2O in the mixed solution is 25:0.1-5.

[0018] The hydrothermal reaction temperature is 160-200° C., and the hydrothermal reaction time is 18-26 hours.

[0019] Among them, in solution A, the concentration of Bi(NO3)3·5H2O is 1-5mmol:30mL; in solution B, the concentration of ZnCl2 is 1-5mmol:20mL; in solution C, the concentration of CdCl2·2.5H2O is 0.1-5mmol:30mL; more preferably, in solution C, the concentration of CdCl2·2.5H2O is 0.9-2mmol:30mL.

[0020] The third object of the present application is to provide the use of the double heterojunction structure material or the double heterojunction structure material prepared by any of the above methods in the photocatalytic reduction of carbon dioxide.

[0021] The double heterojunction structure material selectively reduces carbon dioxide to CH4.

[0022] Beneficial effects of this application:

[0023] The photocatalyst provided in this application is a CdS / Bi2S3 / ZnS composite material, with spherical Bi2S3 as the carrier, and CdS particles and ZnS particles are evenly dispersed on the Bi2S3 surface to form a double heterojunction structure and ternary metal active sites, which can effectively improve the utilization rate of photogenerated electrons, regulate the reduction path of carbon dioxide, and make carbon dioxide more likely to be converted into high-value-added hydrocarbons such as methane.

[0024] Compared with the existing Bi2S3 / ZnS composite photocatalyst, the addition of Cd metal adjusts the CO2 reduction pathway, thereby enhancing the selectivity of CH4. The CH4 yield is as high as 145.08μmol g -1 h -1 Under the same reaction conditions, its performance is 5.54 times, 14.1 times, and 27.16 times higher than that of pure CdS, Bi2S3, and ZnS, respectively; the CH4 electron selectivity reaches 94.2%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a SEM image of different samples, wherein: (a) is the ZnS obtained in Comparative Example 2, (b) is the CdS obtained in Comparative Example 4, (c) is the Bi2S3 obtained in Comparative Example 3, and (d) is the CdS / Bi2S3 / ZnS obtained in Example 1;

[0026] Figure 2 is the HRTEM image of CdS / Bi2S3 / ZnS obtained in Example 1, (a) CdS / Bi2S3 / ZnS, (b) CdS, corresponding to region 1 in (a), (c) ZnS, corresponding to region 2 in (a), (d) Bi2S 3， Corresponding to area 3 in (a); (d) is the inverse Fourier transform of (b), (e) is the inverse Fourier transform of (c), and (f) is the inverse Fourier transform of (d);

[0027] FIG3 is an XRD pattern of different samples obtained in Example 1 and Comparative Examples 2-4;

[0028] FIG4 is a graph showing the UV-visible diffuse reflectance spectra of different samples obtained in Example 1 and Comparative Examples 2-4;

[0029] FIG5 shows the cycle performance of CdS / Bi2S3 / ZnS obtained in Example 1 for CO2 reduction. DETAILED DESCRIPTION

[0030] Below, the technical solution of the present application is described in detail through specific embodiments. However, it should be clearly stated that these embodiments are provided for illustration and are not to be construed as limiting the scope of the present application.

[0031] Example 1

[0032] A double heterojunction material, a CdS / Bi2S3 / ZnS composite material, uses spherical Bi2S3 as a carrier, with CdS and ZnS particles evenly dispersed on the Bi2S3 surface to form a double heterojunction structure. The diameter of the spherical Bi2S3 is 1-3 μm, the diameter of the CdS particles is 20-100 nm, and the diameter of the ZnS particles is 20-100 nm. The molar ratio of ZnS, Bi2S3, and CdS in the CdS / Bi2S3 / ZnS composite material is 3:2:1.8.

[0033] The preparation method includes: weighing 2mmol of bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) and placing it into beaker A, measuring 30mL of deionized water and pouring it into beaker A to obtain solution A, and then stirring the solution at room temperature for 1 hour until the solution A becomes clear; weighing 3mmol of zinc chloride (ZnCl2) and placing it into beaker B, measuring 20mL of deionized water and pouring it into the beaker to obtain solution B, ultrasonicating for 30 minutes, and then stirring the solution at room temperature for 30 minutes; weighing 1.8mmol of cadmium chloride (CdCl2·2.5H2O) and placing it into beaker C, measuring 30mL of deionized water and pouring it into beaker C to obtain solution C, and stirring the solution at room temperature for 1 hour until the solution becomes clear.

[0034] Solutions A, B, and C were sequentially poured into a beaker while stirring. The mixture turned white and opaque and stirred for 5 minutes. 25 mmol of L-cysteine ​​was weighed and placed in a beaker, stirred for 1 hour, and then the mixture was transferred to a hydrothermal autoclave, sealed, and placed in an oven for reaction at 180°C for 22 hours. After the reaction cooled to room temperature, the precipitate was removed from the autoclave and washed several times with deionized water and ethanol. The resulting product was dried in a 60°C oven for 12 hours.

[0035] Example 2

[0036] A double heterojunction structure material, the preparation method of which is different from that of Example 1 only in that the amount of cadmium chloride added is adjusted from "1.8 mmol" to "0.1 mmol", and the other steps and parameters are the same as those of Example 1.

[0037] Example 3

[0038] A double heterojunction structure material, the preparation method of which is different from that of Example 1 only in that the amount of cadmium chloride added is adjusted from "1.8 mmol" to "0.9 mmol", and the other steps and parameters are the same as those of Example 1.

[0039] Example 4

[0040] A double heterojunction structure material, the preparation method of which is different from that of Example 1 only in that the amount of cadmium chloride added is adjusted from "1.8 mmol" to "2 mmol", and the other steps and parameters are the same as those of Example 1.

[0041] Example 5

[0042] A double heterojunction structure material, the preparation method of which is different from that of Example 1 only in that the amount of cadmium chloride added is adjusted from "1.8 mmol" to "5 mmol", and the other steps and parameters are the same as those of Example 1.

[0043] Comparative Example 1

[0044] A CuS / Bi2S3 / ZnS composite photocatalyst, the preparation method of which differs from that of Example 1 only in that 1.8 mmol of cadmium chloride (CdCl2·2.5H2O) is replaced with 1.8 mmol of copper nitrate (Cu(NO3)2·3H2O), and the other steps and parameters are the same as those of Example 1.

[0045] Comparative Example 2

[0046] Synthesis of photocatalyst ZnS:

[0047] Dissolve 3 mmol of zinc chloride in 20 mL of deionized water. Place the solution in an ultrasonic bath for 30 minutes and then stir at room temperature for 30 minutes until the solution turns milky white. Then, add 25 mmol of L-cysteine ​​and stir at room temperature for 1 hour until the solution becomes transparent. The mixed solution is transferred to a sealed, Teflon-lined stainless steel autoclave and allowed to react in an oven at 180°C for 22 hours. After the reaction cools to room temperature, remove the precipitate from the reactor and rinse several times with deionized water and ethanol. The resulting product is dried in an oven at 60°C for 10 hours to yield ZnS.

[0048] Comparative Example 3

[0049] Synthesis of photocatalyst Bi2S3:

[0050] Weigh 2 mmol of bismuth nitrate pentahydrate and 30 mL of deionized water. Slowly pour the deionized water into a beaker and stir the solution at room temperature for 1 hour to clarify. Then, add 25 mmol of L-cysteine ​​to the mixed solution and stir at room temperature for 1 hour until the solution turns green and transparent. The mixed solution is then transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave, sealed, and reacted in an oven at 180°C for 22 hours. After the reaction is cooled to room temperature, remove the precipitate from the reactor and wash it several times with deionized water and ethanol. The resulting product is dried in an oven at 60°C for 12 hours to obtain Bi2S3.

[0051] Comparative Example 4

[0052] Synthesis of photocatalyst CdS:

[0053] Weigh 1.8 mmol of cadmium chloride (CdCl2·2.5H2O) into a clean beaker. Measure 30 mL of deionized water and slowly pour it into the beaker. Stir at room temperature for 1 hour until the solution becomes clear. Then, add 25 mmol of L-cysteine ​​to the mixed solution and stir at room temperature for 1 hour until the solution turns green and transparent. The mixed solution is then transferred to a 100 mL Teflon-lined stainless steel autoclave, sealed, and allowed to react in an oven at 180°C for 22 hours. After the reaction cools to room temperature, remove the precipitate from the autoclave and rinse several times with deionized water and ethanol. The resulting product is dried in an oven at 60°C for 12 hours to yield CdS.

[0054] The photocatalytic activity of the photocatalysts obtained in the above examples and comparative examples was tested, and the test methods and test results are as follows:

[0055] (1) Photocatalytic activity evaluation: The photocatalytic CO2 reduction activity of the catalyst was tested in a 100ml stainless steel reactor using a 300W xenon lamp as the light source and an operating current of 21A. The catalyst (10mg) was evenly dispersed in quartz glass, 18ml deionized water as the solvent, and 2ml TEOA as the sacrificial agent. After five minutes of ultrasonic vibration, it was transferred to a stainless steel reactor. Before the photoreduction CO2 experiment, high-purity CO2 gas (99.995%) was used for ventilation for 2h to exhaust the air in the reactor. Then, the valve at one end of the reactor was closed, and carbon dioxide was introduced until the pressure reached 4bar. The xenon lamp was turned on for illumination. Samples were taken every 1h during the illumination process, and the gas products were detected by gas chromatography (GC-2030).

[0056] (2) After 5 h of illumination, the yields of the reduction products CO and CH4 are shown in Table 1 below:

[0057] Table 1. Yields of reduction products CO and CH4 after 5 h of illumination

[0058] Selectivity calculation formula: is the CO production rate per hour, is the CH4 production rate per hour.

[0059] Comparison of the data in Example 1 and Comparative Example 1 shows that in Comparative Example 1, replacing the cadmium chloride in Example 1 with copper nitrate, the resulting composite photocatalyst exhibited a CH4 electron selectivity of only 42.03%, significantly lower than the 94.2% in Example 1. This demonstrates that not all materials capable of forming a heterojunction structure with Bi2S3 can achieve selective reduction to CH4 using Bi2S3 / ZnS.

[0060] Comparison of the data from Examples 1-5 shows that the CH4 electron selectivities of Examples 1, 3, and 4 are 94.2%, 80.1%, and 89.1%, respectively, which are much higher than those of Examples 2 and 5. This indicates that the molar ratio of CdS, Bi2S3, and ZnS has a significant effect on the selectivity of the double heterojunction structure material.

[0061] Other test results of the samples obtained in the above examples and comparative examples are as follows:

[0062] Figure 1 is a SEM image of different samples, where: (a) is the ZnS obtained in Comparative Example 2, (b) is the CdS obtained in Comparative Example 4, (c) is the Bi2S3 obtained in Comparative Example 3, and (d) is the CdS / Bi2S3 / ZnS obtained in Example 1;

[0063] Figure 2 is the HRTEM image of CdS / Bi2S3 / ZnS obtained in Example 1; (a) CdS / Bi2S3 / ZnS, (b) CdS, corresponding to region 1 in (a), (c) ZnS, corresponding to region 2 in (a), and (d) Bi2S 3， Corresponding to area 3 in (a); (d) is the inverse Fourier transform of (b), (e) is the inverse Fourier transform of (c), and (f) is the inverse Fourier transform of (d);

[0064] Figure 3 is an XRD pattern of different samples obtained in Example 1 and Comparative Examples 2-4; wherein, ZnS corresponds to the sample in Comparative Example 2, CdS corresponds to the sample in Comparative Example 4, Bi2S3 corresponds to the sample in Comparative Example 3, and ZnBiCdS corresponds to the CdS / Bi2S3 / ZnS composite material obtained in Example 1;

[0065] Figure 4 is a graph of the UV-visible diffuse reflectance spectra of different samples obtained in Example 1 and Comparative Examples 2-4; wherein, ZnS corresponds to the sample in Comparative Example 2, CdS corresponds to the sample in Comparative Example 4, Bi2S3 corresponds to the sample in Comparative Example 3, and Bi2S3 / ZnS / CdS corresponds to the CdS / Bi2S3 / ZnS composite material obtained in Example 1;

[0066] FIG5 shows the cycle performance of CdS / Bi2S3 / ZnS obtained in Example 1 for CO2 reduction.

[0067] The above is only a preferred specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes based on the technical solution and application concept of the present application within the technical scope disclosed in the present application, and they should be covered by the scope of protection of the present application.

Claims

1. A double heterojunction structure material, which is a CdS / Bi2S3 / ZnS composite material, with spherical Bi2S3 as a carrier, CdS particles and ZnS particles uniformly dispersed on the surface of Bi2S3 to form a double heterojunction structure; the molar ratio of ZnS, Bi2S3 and CdS in the CdS / Bi2S3 / ZnS composite material is 3:1:0.1-5.

2. The double heterojunction structure material according to claim 1, wherein: The diameter of spherical Bi2S3 is 1-3μm, the diameter of CdS particles is 20-100nm, and the diameter of ZnS particles is 20-100nm.

3. The double heterojunction structure material according to claim 1, wherein: The molar ratio of ZnS, Bi2S3 and CdS in the CdS / Bi2S3 / ZnS composite material is 3:2:0.9-2.

4. A method for preparing a double heterojunction structure material, comprising: Dissolve Bi(NO3)3·5H2O in ethylene glycol solution to obtain solution A; dissolve ZnCl2 in water to obtain solution B; dissolve CdCl2·2.5H2O in water to obtain solution C; mix solutions A, B and C, add L-cysteine ​​to the mixture, perform hydrothermal reaction, wash and dry to obtain CdS / Bi2S3 / ZnS composite material; The molar ratio of ZnCl2, Bi(NO3)3·5H2O and CdCl2·2.5H2O in the mixed solution is 3:2:0.1-5.

5. The method for preparing a double heterojunction structure material according to claim 4, wherein: The molar ratio of ZnCl2, Bi(NO3)3·5H2O and CdCl2·2.5H2O in the mixed solution is 3:2:0.9-2.

6. The method for preparing a double heterojunction structure material according to claim 4, wherein: The molar ratio of L-cysteine ​​to CdCl2·2.5H2O in the mixed solution is 25:0.1-5.

7. The method for preparing a double heterojunction structure material according to claim 4, wherein: The hydrothermal reaction temperature is 160-200°C, and the hydrothermal reaction time is 18-26h.

8. The method for preparing a double heterojunction structure material according to claim 4, wherein: In solution A, the concentration of Bi(NO3)3·5H2O is 1-5mmol:30mL; in solution B, the concentration of ZnCl2 is 1-5mmol:20mL; in solution C, the concentration of CdCl2·2.5H2O is 0.1-5mmol:30mL.

9. Use of the double heterojunction structure material according to claim 1 in photocatalytic reduction of carbon dioxide.

10. The use according to claim 9, wherein: The double heterojunction structure material selectively reduces carbon dioxide to CH4.

11. Use of the double heterojunction structure material prepared by the preparation method according to claim 4 in photocatalytic reduction of carbon dioxide.

12. The use according to claim 11, wherein: The double heterojunction structure material selectively reduces carbon dioxide to CH4.

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