Bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FT0 photoelectrode and preparation method and application thereof

Abstract

The invention provides a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FT0 photoelectrode and a preparation method and application thereof, and belongs to the technical field of photoelectrochemistry. Bismuth nitrate pentahydrate serves as a raw material, bismuth oxyhalide crystals are formed on FTO through the reaction between halide and bismuth nitrate and in combination with an additive, bismuth oxyhalide-bismuth oxysulfide heterojunction is synthesized on the FTO through in-situ conversion by taking the bismuth oxyhalide crystals as a precursor, and the in-situ heterojunction photoelectrode with excellent photoelectric performance is prepared. A simple hot solvent method is adopted, operation is easy and convenient, low-cost raw materials are adopted, and the production cost is reduced. And meanwhile, in-situ conversion can enable a close-contact heterojunction interface to be formed between bismuth oxyhalide and bismuth oxysulfide, so that the response of an electrode to light is improved, the transfer of current-carrying electrons of the composite material is promoted, and the photoelectric property is greatly improved. And a new thought and method for in-situ synthesis of the heterojunction photoelectrode on the FTO is provided for the photoelectrochemical application industry.

Description

Technical Field

[0001] The present invention relates to the field of photoelectrochemical technology, and in particular to a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode and a preparation method and application thereof. Background Art

[0002] The research on photoelectrodes is mainly due to the need for the development of photoelectrochemical materials. In photoelectrochemistry, the response of electrode materials to light and the migration efficiency of current-carrying electrons greatly affect the effects of photoelectrochemistry in applications such as sensors, photocatalytic degradation, hydrogen production and carbon dioxide reduction. The research on photoelectrodes is to prepare a material that is sensitive to light, has a fast response speed and high electron transfer efficiency to promote the development of various applications in the field of photoelectrochemistry.

[0003] In recent years, atomically thin layered materials, such as graphene, hexagonal boron nitride, transition metal sulfides, and perovskites, have great application backgrounds in optoelectronics, catalysis, and energy storage due to their unique physical and chemical properties. Among the above-mentioned layered structures, bismuth oxyhalide (BiOX, X=Cl, Br, I) has a more stable crystal structure, excellent physical and chemical properties, and the material itself is non-toxic, low in preparation cost, and corrosion-resistant, so it has become a typical representative of a new type of sheet structure. The layers rely on van der Waals forces and are stacked along the c-axis in the form of X-Bi-O-Bi-X. In each layer, a bismuth atom is surrounded by 4 oxygen atoms and 4 halogen atoms, forming an asymmetric decahedral geometric structure. The covalent bonds within the layers and the van der Waals forces between the layers enhance the anisotropy, electrical, optical, and mechanical toughness of this structure. This means that bismuth oxyhalide materials have great application potential in many fields such as catalysis, biology, and optoelectronics.

[0004] However, due to the high recombination rate of photogenerated electron-hole pairs and the narrow light absorption range, the photocatalytic activity of the original bismuth oxyhalide is still unsatisfactory. So far, many strategies have been used to improve the photocatalytic performance. Heterojunction is the most commonly used method to improve the photocatalytic performance of materials. Although some progress has been made, most traditional heterojunctions are based on the random mixing of two synthetic semiconductor materials, which is not conducive to improving the mobility of current-carrying electrons. This, to a certain extent, limits the further enhancement of the photoelectric performance of bismuth oxyhalide.

[0005] Recently, bismuth oxysulfide, a zippered two-dimensional (2D) material belonging to the layered bismuth oxysulfide (Bi 2O 2X: X = S, Se, Te) family, has been shown to be a potential candidate for photovoltaic materials due to its good band gap (1.5 eV), efficient charge dissociation, high carrier mobility, and long carrier lifetime. Similar to bismuth oxyhalides, bismuth oxysulfide crystals are also composed of alternating stacks of [Bi2O2]2+ layers and sulfide layers, and the two crystals have similar layered structures.

[0006] As one of the most commonly used substrates for photoelectrodes, FTO has the advantages of good visible light transmittance, large UV absorption coefficient, low resistivity, stable chemical properties, and strong acid and alkali resistance at room temperature. However, most FTO photoelectrodes use the drop casting method to attach the synthesized material solution to the FTO board. Due to the loose fit, the material often detaches and the electrical response is weak.

[0007] Therefore, it is of great significance to study a photoelectrode with high photoelectric performance, low resistivity, high current-carrying electron mobility and not easy to fall off from the substrate. Summary of the invention

[0008] In view of this, the present invention proposes a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode and a preparation method and application thereof to solve the above problems.

[0009] The technical solution of the present invention is achieved as follows: a method for preparing a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode, comprising the following steps:

[0010] S1. Mixing a halide with an organic solvent and stirring to completely dissolve the mixture to form a halide solution, and simultaneously mixing bismuth nitrate pentahydrate with an organic solvent and stirring to dissolve the mixture to form a bismuth solution; mixing the halide solution and the bismuth solution in a volume ratio of 1:1-2 and stirring to form a mixed solution;

[0011] S2, placing the conductive surface of the FTO plate downward in a high-pressure reactor, adding the above mixed solution, controlling the temperature at 140°C-160°C, and reacting for 8-12 hours. After the reaction, take out the FTO plate, rinse it with anhydrous ethanol and deionized water three times respectively, and place it in a vacuum drying oven at 60-70°C for 4-12 hours to obtain a bismuth oxyhalide FTO electrode plate;

[0012] S3. After ultrasonicating thiourea and deionized water for 5-15 minutes, completely dissolve them to obtain a sulfur solution. Then, the bismuth oxyhalide FTO electrode plate obtained in S2 is subjected to a hydrothermal reaction with the sulfur solution in a high-pressure reactor. The temperature is controlled to be 180-200°C and the reaction time is 1-3h. After the reaction, the FTO electrode plate is taken out and rinsed three times with anhydrous ethanol and deionized water respectively and placed in a vacuum drying oven at 60-70°C for 4-8h. Then, the dried sample is placed in a muffle furnace for calcination. After naturally cooling with the furnace, a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode is obtained.

[0013] Furthermore, the ratio of the halide of S1 to the organic solvent is 1.25-3mmol:15mL.

[0014] Furthermore, the halide of S1 is any one of sodium chloride, potassium chloride, potassium iodide, potassium bromide, hexadecyltrimethylammonium bromide (CTAB) and sodium bromide.

[0015] Furthermore, the ratio of bismuth nitrate pentahydrate to the organic solvent in S1 is 1-2 mmol:15-30 ml.

[0016] Furthermore, the organic solvent is any one or a combination of anhydrous ethanol, ethylene glycol and triethanolamine.

[0017] Furthermore, the ratio of thiourea to deionized water in S3 is 3-6 mmol:50 mL.

[0018] Furthermore, the calcination temperature in the muffle furnace of S3 is 300-400°C, the calcination time is 1-3h, and the heating rate of the muffle furnace is 5°C / min.

[0019] Furthermore, a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FT0 photoelectrode is prepared by the above preparation method.

[0020] Furthermore, an in-situ heterojunction FT0 photoelectrode of bismuth oxyhalide-bismuth oxysulfide was applied in an electrochemical workstation.

[0021] Furthermore, the working voltage applied to the photoelectrode in the electrochemical workstation is 0.4-0.7V, the light source is 420nm-630nm, and the light switching time is 20s.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] Bismuth oxyhalide-bismuth oxysulfide electrodes are directly synthesized on FTO boards through an in-situ conversion strategy to efficiently promote the separation and transmission of carriers and expand the range of light absorption. Among them, because bismuth oxysulfide is converted in situ from bismuth oxyhalide as a precursor, the heterostructure is more compact, which is conducive to promoting carrier interface migration and enhancing material stability. And it is synthesized directly on the FTO board, the material is not easy to fall off, and the photoelectric performance of the heterostructure can be maximized. Specifically, 1) the photoelectrode is grown directly on FTO, the operation is simple and it is not easy to fall off FTO; 2) the heterojunction is converted in situ, the structure is more compact, and the photoelectric performance improvement effect is greater; 3) a variety of heterojunctions can be synthesized using bismuth oxyhalide as a precursor. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the XRD pattern of the bismuth oxychloride-bismuth oxysulfide in-situ heterojunction obtained in Example 1.

[0025] Figure 2 This is the XRD pattern of the bismuth oxybromide-bismuth oxysulfide in-situ heterojunction obtained in Example 2.

[0026] Figure 3 This is the photocurrent response spectrum of the photoelectrode material obtained in Example 1.

[0027] Figure 4 This is the photocurrent response spectrum of the photoelectrode material obtained in Example 2. DETAILED DESCRIPTION

[0028] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0029] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0030] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0031] Example 1

[0032] 2mmol sodium chloride was mixed with 15ml ethylene glycol to obtain a sodium chloride solution, and 2mmol bismuth nitrate pentahydrate was mixed with 15ml ethylene glycol to obtain a bismuth solution. The sodium chloride solution was added dropwise to the bismuth solution in a volume ratio of 1:1. After stirring for 30 minutes, the FTO substrate was placed in a reactor with the conductive surface facing down and the prepared mixed solution was added. The reaction was carried out at 160°C for 12 hours to grow bismuth oxychloride. After the sample was taken out, it was rinsed three times with anhydrous ethanol and deionized water respectively and dried in a vacuum drying oven at 80°C for 12 hours.

[0033] After ultrasonicating 4 mmol thiourea in 50 ml deionized water for 10 minutes, the FTO board with bismuth oxychloride grown on it was placed in a reactor with the conductive surface facing down and the prepared thiourea solution was added, followed by reaction at 180°C for 2.5 hours. After the reaction, the sample was rinsed three times with deionized hydrated anhydrous ethanol respectively and dried in a 60°C vacuum drying oven for 4 hours. Afterwards, the sample was calcined in a muffle furnace at a calcination temperature of 400°C for 1.5 hours and a muffle furnace heating rate of 5°C / min. After calcination, the sample was naturally cooled with the furnace to obtain a bismuth oxychloride-bismuth oxysulfide in-situ heterojunction photoelectrode material. After measurement, Figure 1 This is the XRD pattern of the obtained bismuth oxychloride-bismuth oxysulfide in-situ heterojunction.

[0034] Using a xenon lamp as the light source, the photoelectric properties of the obtained samples were characterized with the aid of an electrochemical workstation. The test settings were: turn on the light for 20 seconds, turn off the light for 20 seconds, cycle 3 times, and record the photocurrent response of the samples.

[0035] Test related performance and properties such as Figure 3 :

[0036] Compared with pure bismuth oxychloride, the photocurrent density of the in situ heterojunction sample is significantly enhanced. This is because the in situ assembly of bismuth oxysulfide can improve the photoresponse, thereby greatly enhancing the photoelectric performance of the photoelectrode.

[0037] Example 2

[0038] 1.25mmol hexadecyltrimethylammonium bromide and 15mL organic solvent were mixed and stirred to obtain an ammonium solution, and 1.25mmol bismuth nitrate pentahydrate and 15ml ethylene glycol were mixed and stirred to obtain a bismuth solution. The organic solvent was a mixed solution of anhydrous ethanol and ethylene glycol in a volume ratio of 2:1. The ammonium solution was added dropwise to the bismuth solution in a volume ratio of 1:1, and after stirring for 30 minutes, the FTO substrate conductive surface was placed in a reactor with the configured mixed solution facing down, and the mixture was added to react at 140℃ for 10 hours to grow bismuth oxybromide. After the sample was taken out, it was rinsed three times with anhydrous ethanol and deionized water respectively and placed in a vacuum drying oven at 60℃ for 8 hours. After ultrasonicating 5mmol thiourea and 50ml deionized water for 15 minutes, the FTO board with bismuth oxybromide grown was placed in a reactor with the conductive surface facing down and the configured thiourea solution was added to react at 190℃ for 2 hours. After the reaction, the sample was rinsed three times with deionized water and anhydrous ethanol respectively and placed in a vacuum drying oven at 60℃ for 4 hours. Afterwards, the sample was calcined in a muffle furnace at a temperature of 350°C for 2 hours and a heating rate of 5°C / min. After calcination, the sample was naturally cooled in the furnace to obtain a bismuth oxybromide-bismuth oxysulfide in-situ heterojunction photoelectrode material. Figure 2 This is the XRD pattern of the obtained bismuth oxybromide-bismuth oxysulfide in-situ heterojunction.

[0039] Using a xenon lamp as the light source, the photoelectric properties of the obtained samples were characterized with the aid of an electrochemical workstation. The test settings were: turn on the light for 20 seconds, turn off the light for 20 seconds, cycle 3 times, and record the photocurrent response of the samples.

[0040] Test related performance and properties such as Figure 4 :

[0041] Compared with pure bismuth oxybromide, the in-situ heterojunction sample exhibits a stronger photocurrent response, which indicates that the heterojunction formed by in-situ assembled bismuth oxysulfide can greatly enhance the photoelectric performance of the photoelectrode.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode, characterized in that: The following steps are involved: S1. Mixing a halide with an organic solvent and stirring to completely dissolve the mixture to form a halide solution, and simultaneously mixing bismuth nitrate pentahydrate with an organic solvent and stirring to dissolve the mixture to form a bismuth solution; mixing the halide solution and the bismuth solution in a volume ratio of 1:1-2 and stirring to form a mixed solution; S2, placing the conductive surface of the FTO plate downward in a high-pressure reactor, adding the above mixed solution, controlling the temperature at 140°C-160°C, and reacting for 8-12 hours. After the reaction, take out the FTO plate, rinse it with anhydrous ethanol and deionized water three times respectively, and place it in a vacuum drying oven at 60-70°C for 4-12 hours to obtain a bismuth oxyhalide FTO electrode plate; S3. After ultrasonicating thiourea and deionized water for 5-15 minutes, completely dissolve them to obtain a sulfur solution. Then, the bismuth oxyhalide FTO electrode plate obtained in S2 is subjected to a hydrothermal reaction with the sulfur solution in a high-pressure reactor. The temperature is controlled to be 180-200°C and the reaction time is 1-3h. After the reaction, the FTO electrode plate is taken out and rinsed three times with anhydrous ethanol and deionized water respectively and placed in a vacuum drying oven at 60-70°C for 4-8h. Then, the dried sample is placed in a muffle furnace for calcination. After naturally cooling with the furnace, a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode is obtained.

2. The method for preparing a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode according to claim 1, characterized in that: The ratio of the halide of S1 to the organic solvent is 1.25-3mmol:15mL.

3. The method for preparing a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode according to claim 1, characterized in that: The halide of S1 is any one of sodium chloride, potassium chloride, potassium iodide, potassium bromide, cetyltrimethylammonium bromide (CTAB) and sodium bromide.

4. The method for preparing a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode according to claim 1, characterized in that: The ratio of bismuth nitrate pentahydrate to the organic solvent in S1 is 1-2mmol:15-30ml.

5. The method for preparing a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode according to claim 2 or 4, characterized in that: The organic solvent is any one or a combination of anhydrous ethanol, ethylene glycol and triethanolamine.

6. The method for preparing a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode according to claim 1, characterized in that: The ratio of thiourea to deionized water in S3 is 3-6 mmol:50 mL.

7. The method for preparing a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode according to claim 1, characterized in that: The calcination temperature in the muffle furnace of S3 is 300-400°C, the calcination time is 1-3h, and the heating rate of the muffle furnace is 5°C / min.

8. A bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7.

9. Use of a bismuth oxyhalide-bismuth oxysulfide in-situ heterojunction FTO photoelectrode as claimed in claim 1 in an electrochemical workstation.

10. The use according to claim 9, characterized in that The working voltage applied by the photoelectrode in the electrochemical workstation is 0.4-0.7V, the light source is 420nm-630nm, and the light switching time is 20s.

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