Z-type photocatalyst, preparation method and application thereof

Abstract

This invention discloses a method for preparing a Z-type photocatalyst based on CoPc / Bi₂WO₆(BWO). The method uses Na₂WO₄·2H₂O, Bi(NO₃)₃·5H₂O, and CoPc(II) as raw materials, and ethanol and deionized water as polar solvents, employing a hydrothermal method. The microstructure of the prepared Z-type photocatalyst exhibits two-dimensional nanoplates with lengths in the range of approximately 50-100 nm. This heterojunction structure provides a conductive pathway for carrier transfer, thereby reducing the electron-hole recombination rate and further improving photocatalytic performance. This invention demonstrates that the Z-type heterojunction formed by CoPc / Bi₂WO₆(BWO) can achieve hole trapping and spatial separation and transfer of charge carriers, exhibiting excellent photocatalytic CO₂ reduction activity, opening up new prospects for designing advanced solar energy conversion systems.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor photocatalysis, specifically relating to a Z-type photocatalyst based on CoPc / Bi2WO6 (BWO), its preparation method, and its application. Technical Background

[0002] Currently, our energy needs are met through technologies that emit carbon dioxide, which negatively impact humans and their lives due to climate change and global warming. To mitigate these problems, decarbonizing energy systems is urgently needed. Photocatalysis, by converting CO2 into benign and environmentally friendly products, has the potential to play a crucial role in reducing CO2 emissions.

[0003] Recently, semiconductor-based photocatalysis has attracted considerable attention for CO2 reduction reactions. However, research in photocatalytic CO2 reduction (PCR) is still in its infancy. Developing highly efficient PCR photocatalysts is an ongoing process. To overcome the efficiency bottlenecks in existing PCR photocatalysts, the design of advanced photocatalysts should focus on extended visible light absorption and efficient charge separation and transport. Creating heterojunctions between asymmetric catalysts is a feasible strategy to enhance the absorption of longer wavelength photons and the spatial separation and transfer of electron-hole pairs.

[0004] The actual efficiency of heterojunction photocatalysts depends primarily on the physicochemical properties of the participating catalysts. Although heterojunction photocatalysts are more advantageous than single photocatalysts, charge carrier loss due to recombination and the lack of suitable catalytic sites for redox reactions are several major challenges that have not yet been overcome.

[0005] The construction of Bi₂WO₆-based z-scheme heterojunctions has been reported, exhibiting good catalytic activity. This is attributed to the internal electric field induced by the different electronic band structures, which may further facilitate the transfer and separation of charge carriers through the heterostructure. This Bi₂WO₆-based heterojunction and its application in the reduction of CO₂ to useful products have been discussed. However, current reports are limited, and the prepared inorganic composites still exhibit poor photocatalytic CO₂ reduction activity due to the lack of active catalytic sites. Therefore, introducing a novel integrated z-scheme heterojunction with abundant active sites and a broad response to the solar spectrum is a feasible strategy. Summary of the Invention

[0006] To address the problems existing in the background technology, the present invention provides a Z-type photocatalyst based on CoPc / Bi2WO6 (BWO), its preparation method, and its application.

[0007] The present invention specifically adopts the following technical solution:

[0008] A method for preparing a Z-type photocatalyst based on CoPc / Bi2WO6 (BWO) is disclosed. The photocatalyst is prepared by hydrothermal method using Na2WO4·2H2O, Bi(NO3)3·5H2O, and CoPc (II) as raw materials and ethanol and deionized water as polar solvents.

[0009] Furthermore, the preparation method of the Z-type photocatalyst based on CoPc / Bi2WO6 (BWO) includes the following steps:

[0010] (1) Dissolve a certain proportion of Na2WO4·2H2O and Bi(NO3)3·5H2O in deionized water to obtain a mixture;

[0011] (2) After stirring for a period of time, transfer the mixture obtained in step (1) into a 100ml Teflon-lined stainless steel autoclave and keep it at a certain temperature for a period of time.

[0012] (3) A white precipitate was obtained by centrifugation, and then washed repeatedly with deionized water and ethanol. The precipitate was then dried in an oven to obtain Bi2WO6 nanosheets.

[0013] (4) Disperse the prepared Bi2WO6 powder in ethanol and sonicate it for a period of time to form a Bi2WO6 suspension. Then, add a certain amount of commercial CoPc to the Bi2WO6 suspension and stir.

[0014] (5) The sample was ultrasonically treated for a period of time, then stirred at a certain temperature for a period of time, and then the product was separated by centrifugation and then dried in a vacuum oven to obtain a Z-type photocatalyst based on CoPc / Bi2WO6(BWO).

[0015] Further, the Na2WO4·2H2O and Bi(NO3)3·5H2O mentioned in step (1) are 0.3-0.4g and 0.9-1.0g, respectively.

[0016] Furthermore, the stirring time in step (2) is 1-1.5 hours, and the temperature is maintained at 160℃ for 22-25 hours.

[0017] Furthermore, in step (3), drying is carried out in an oven at a temperature of 75-85℃.

[0018] Further, 1-1.5g of Bi2WO6 powder in step (4) is dispersed in 30ml of ethanol.

[0019] Furthermore, in step (5), the mixture is stirred for another 6-7 hours at a constant temperature of 70°C.

[0020] Further, in step (5), the product is ultrasonically treated for 30-60 minutes, then separated by centrifugation, and then dried in a vacuum oven at 45-70°C.

[0021] This invention also provides the application of a CoPc / Bi2WO6 (BWO)-based Z-type photocatalyst in the photocatalytic production of CO and CH4 from CO2.

[0022] The present invention has the following beneficial effects:

[0023] In this invention, Na₂WO₄·2H₂O, Bi(NO₃)₃·5H₂O, and CoPc(II) were used as raw materials, and ethanol and deionized water were used as polar solvents, prepared by a hydrothermal method. CoPc possesses suitable conduction band positions, strong oxygen activation ability, and a strong bonding affinity for O₂, providing Co-N₄(II) active centers for catalytic reduction. Furthermore, these M-N₄(II) sites can act as electron pumps in the composite material to achieve rapid transfer of photogenerated charge carriers and capture more photogenerated electrons, which migrate from the semiconductor composite material, thereby enhancing the photocatalytic reduction reaction. Under visible light conditions, the CH₄(CO) yield of the synthesized CoPc / BWO direct Z-Scheme heterojunction was increased by 2.3 times (5.2 times) compared to pure BWO. BWO and CoPc promoted the formation of the direct Z-scheme system, described the charge transfer mechanism from BWO to CoPc, and promoted charge separation caused by the built-in electric field (BIEF) and interfacial double-w bridging in the CoPc / BWO heterojunction. Simultaneously, it enhances light absorption capacity while maintaining a high redox potential. Furthermore, the Co-N4(II) active sites of the CoPc dye capture more photogenerated electrons, promoting electron localization at O2 and exhibiting excellent CO2 photoreduction activity. This work may open new prospects for designing advanced solar energy conversion schemes. Attached Figure Description

[0024] Figure 1 Transmission electron microscopy image of the Z-type photocatalyst based on CoPc / Bi2WO6 (BWO) prepared in this embodiment;

[0025] Figure 2 HRTEM image of the Z-type photocatalyst based on CoPc / Bi2WO6 (BWO) prepared in this embodiment;

[0026] Figure 3 This is the X-ray diffraction pattern of the Z-type photocatalyst based on CoPc / Bi2WO6 (BWO) prepared in this embodiment;

[0027] Figure 4This is a graph showing the photocatalytic CO2 reduction performance of the Z-type photocatalyst based on CoPc / Bi2WO6 (BWO) prepared in this embodiment.

[0028] Specific Implementation Cases

[0029] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0030] In this embodiment of the invention, the preparation method of the Z-type photocatalyst based on CoPc / Bi2WO6 (BWO) includes the following steps:

[0031] (1) Dissolve a certain proportion of Na2WO4·2H2O and Bi(NO3)3·5H2O in deionized water to obtain a mixture;

[0032] (2) After stirring for a period of time, transfer the mixture obtained in step (1) into a 100ml Teflon-lined stainless steel autoclave and keep it at a certain temperature for a period of time.

[0033] (3) A white precipitate was obtained by centrifugation, and then washed repeatedly with deionized water and ethanol. The precipitate was then dried in an oven to obtain CoPc / Bi2WO6(BWO) nanosheets.

[0034] (4) Disperse the prepared Bi2WO6 powder in ethanol and sonicate it for a period of time to form a Bi2WO6 suspension. Then, add a certain amount of commercial CoPc to the Bi2WO6 suspension and stir.

[0035] (5) The sample was ultrasonically treated for a period of time, then stirred at a certain temperature for a period of time, and then the product was separated by centrifugation and then dried in a vacuum oven to obtain a Z-type photocatalyst based on CoPc / Bi2WO6(BWO).

[0036] To make the present invention more fully disclosed, more specific embodiments are described below.

[0037] Example 1

[0038] A method for preparing a Z-type photocatalyst based on CoPc / Bi2WO6 (BWO) includes the following steps:

[0039] (1) 0.332 g (1 mmol) of Na2WO4·2H2O and 0.986 g (2 mmol) of Bi(NO3)3·5H2O were effectively dissolved in 80 mL of deionized water;

[0040] (2) After stirring for 1 hour, transfer the mixture to a 100ml Teflon-lined stainless steel autoclave and maintain the temperature at 160℃ for 24 hours.

[0041] (3) A white precipitate was obtained by centrifugation, and then washed repeatedly with deionized water and ethanol. The precipitate was then dried in an oven at 80°C to obtain Bi2WO6 nanosheets.

[0042] (4) Disperse 1g of the prepared Bi2WO6 powder in 30ml of ethanol and sonicate for 30min to form a Bi2WO6 suspension. Then, add commercial CoPc to the Bi2WO6 suspension and stir. The mass ratio of commercial CoPc to Bi2WO6 is 1%.

[0043] (5) The sample was ultrasonically treated for 30 minutes, then stirred at 70°C for 6 hours. Subsequently, the product was separated by centrifugation and then dried in a vacuum oven at 60°C to obtain a Z-type photocatalyst based on CoPc / Bi2WO6(BWO).

[0044] Photocatalysis experiment: 0.1 g of Z-type photocatalyst powder was dispersed in 5 mL of water and then added to the reactor. High-purity CO2 gas was passed through the water and then into the reaction apparatus to reach ambient pressure. The photocatalyst was equilibrated in the CO2 / H2O system for 20 minutes, followed by irradiation for 4 hours. During irradiation, 250 μL of gaseous reactants were extracted from the reaction tank at regular intervals, and the concentrations of CO, CH4, etc., were analyzed using a gas chromatograph (CO and CH4 were analyzed using a Techcomp GC-7920 with an FID detector; O2 was analyzed using a Techcomp GC-7900 with a TCD detector).

[0045] Figure 1 The image shows a transmission electron microscope (TEM) image of the CoPc / Bi2WO6(BWO)-based Z-type photocatalyst prepared in this embodiment. As can be seen from the image, the surface and interface morphology of the CoPc / Bi2WO6(BWO)-based Z-type photocatalyst is a two-dimensional nanoplate with a length of approximately 50-100 nm.

[0046] Figure 2 The image shows an HRTEM image of the Z-type photocatalyst based on CoPc / Bi2WO6 (BWO) prepared in this embodiment. The HRTEM image shows that the spacing between the markers is 0.272 nm, which coincides with the (002) plane of Bi2WO6. EDX elemental mapping confirmed the presence of Bi, W, O, C, N, and Co, and further confirmed the CoPc / BWO composite formation.

[0047] Figure 3This is the X-ray diffraction pattern of the Z-type photocatalyst based on CoPc / Bi₂WO₆ (BWO) prepared in this embodiment. As shown in the figure, all diffraction peaks belong to the orthorhombic Bi₂WO₆ phase (JCPDS = No. 73-2020). Due to the low concentration and high dispersibility of the dye, no additional peaks appeared in the XRD pattern for x% CoPc / BWO (x = 1, 2, and 3 wt.%). The slight rightward shift of the high-intensity peaks further confirms the composite formation.

[0048] Figure 4 The figure shows the photocatalytic CO2 reduction performance of the Z-type photocatalyst based on CoPc / Bi2WO6(BWO) prepared in this embodiment. As can be seen from the figure, the rate of CO and CH4 production by the Z-type photocatalyst based on CoPc / Bi2WO6(BWO) increases almost linearly with the extension of irradiation time. Moreover, during the 6-hour collection process, its photocatalytic performance did not show significant attenuation, indicating that the structure of the Z-type photocatalyst based on CoPc / Bi2WO6(BWO) prepared in this invention is relatively stable.

[0049] Example 2

[0050] A method for preparing a Z-type photocatalyst based on CoPc / Bi2WO6 (BWO) includes the following steps:

[0051] (1) 0.332 g (1 mmol) of Na2WO4·2H2O and 0.986 g (2 mmol) of Bi(NO3)3·5H2O were effectively dissolved in 80 mL of deionized water;

[0052] (2) After stirring for 1 hour, transfer the mixture to a 100ml Teflon-lined stainless steel autoclave and maintain the temperature at 160℃ for 24 hours.

[0053] (3) A white precipitate was obtained by centrifugation, and then washed repeatedly with deionized water and ethanol. The precipitate was then dried in an oven at 80°C to obtain Bi2WO6 nanosheets.

[0054] (4) Disperse 1g of the prepared Bi2WO6 powder in 30ml of ethanol and sonicate for 30min to form a Bi2WO6 suspension. Then, add commercial CoPc to the Bi2WO6 suspension and stir. The mass ratio of commercial CoPc to Bi2WO6 is 2%.

[0055] (5) The sample was ultrasonically treated for 30 minutes, then stirred at 70°C for 6 hours. Subsequently, the product was separated by centrifugation and then dried in a vacuum oven at 60°C to obtain a Z-type photocatalyst based on CoPc / Bi2WO6(BWO).

[0056] Example 3

[0057] A method for preparing a Z-type photocatalyst based on CoPc / Bi2WO6 (BWO) includes the following steps:

[0058] (1) 0.332 g (1 mmol) of Na2WO4·2H2O and 0.986 g (2 mmol) of Bi(NO3)3·5H2O were effectively dissolved in 80 mL of deionized water;

[0059] (2) After stirring for 1 hour, transfer the mixture to a 100ml Teflon-lined stainless steel autoclave and maintain the temperature at 160℃ for 24 hours.

[0060] (3) A white precipitate was obtained by centrifugation, and then washed repeatedly with deionized water and ethanol. The precipitate was then dried in an oven at 80°C to obtain Bi2WO6 nanosheets.

[0061] (4) Disperse 1g of the prepared Bi2WO6 powder in 30ml of ethanol and sonicate for 30min to form a Bi2WO6 suspension. Then, add a certain amount of commercial CoPc to the Bi2WO6 suspension and stir. The mass ratio of commercial CoPc to Bi2WO6 is 3%.

[0062] (5) The sample was ultrasonically treated for 30 minutes, then stirred at 70°C for 6 hours. Subsequently, the product was separated by centrifugation and then dried in a vacuum oven at 60°C to obtain a Z-type photocatalyst based on CoPc / Bi2WO6(BWO).

Claims

1. A method for preparing a Z-type photocatalyst based on CoPc / Bi2WO6, characterized in that: The photocatalyst was prepared by hydrothermal method using Na2WO4·2H2O, Bi(NO3)3·5H2O, and CoPc(II) as raw materials and ethanol and deionized water as polar solvents. The method for preparing the Z-type photocatalyst based on CoPc / Bi2WO6 includes the following steps: (1) Dissolve a certain proportion of Na2WO4·2H2O and Bi(NO3)3·5H2O in deionized water to obtain a mixture; (2) After stirring for a period of time, transfer the mixture obtained in step (1) into a 100mL Teflon-lined stainless steel autoclave and keep it at a certain temperature for a period of time. (3) A white precipitate was obtained by centrifugation, and then washed repeatedly with deionized water and ethanol. The precipitate was then dried in an oven to obtain Bi2WO6 nanosheets. (4) Disperse the prepared Bi2WO6 powder in ethanol and sonicate it for a period of time to form a Bi2WO6 suspension. Then, add CoPc to the Bi2WO6 suspension and stir. The mass ratio of CoPc to Bi2WO6 is 1%-3%. (5) The sample was ultrasonically treated for a period of time, then stirred at a certain temperature for a period of time, and then the product was separated by centrifugation and then dried in a vacuum oven to obtain a Z-type photocatalyst based on CoPc / Bi2WO6. The amounts of Na2WO4·2H2O and Bi(NO3)3·5H2O mentioned in step (1) are 0.3-0.4g and 0.9-1.0g, respectively; The stirring time in step (2) is 1-1.5 hours, and the temperature is maintained at 160℃ for 22-25 hours; In step (3), drying is carried out in an oven at a temperature of 75-85℃.

2. The method for preparing the Z-type photocatalyst based on CoPc / Bi2WO6 according to claim 1, characterized in that, In step (4), 1-1.5g of Bi2WO6 powder is dispersed in 30ml of ethanol.

3. The method for preparing the Z-type photocatalyst based on CoPc / Bi2WO6 according to claim 1, characterized in that, In step (5), stir for another 6-7 hours at a constant temperature of 70℃.

4. The method for preparing the Z-type photocatalyst based on CoPc / Bi2WO6 according to claim 1, characterized in that, In step (5), the product is ultrasonically treated for 30-60 minutes, then separated by centrifugation, and then dried in a vacuum oven at 45-70°C.

5. A Z-type photocatalyst based on CoPc / Bi2WO6 prepared by the preparation method according to any one of claims 1-4.

6. The application of the Z-type photocatalyst based on CoPc / Bi2WO6 according to claim 5 in the photocatalytic production of CO and CH4 from CO2.

Images