A Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst, its preparation method and application

Abstract

This invention discloses a Cu2O-Bi vacancy-Bi2WO6 heterojunction photocatalyst, its preparation method, and its applications, belonging to the field of photocatalytic materials technology. The Cu2O-Bi vacancy-Bi2WO6 heterojunction photocatalyst contains 10%-30% Cu2O by molar percentage. The preparation method includes: taking CTAB and CuSO4·5H2O, heating and stirring, adding ascorbic acid, continuing stirring, adding Bi vacancy-Bi2WO6, continuing stirring, adjusting the pH of the resulting mixed solution, continuing stirring, cooling, washing, and vacuum drying to obtain Cu2O-Bi vacancy-Bi2WO6. Compared with existing photocatalysts, the Cu2O-Bi vacancy-Bi2WO6 heterojunction photocatalyst provided by this invention has high efficiency in responding to CO2 and good stability. The strong built-in electric field at the heterojunction interface not only accelerates the separation and transfer of charge carriers but also enhances the adsorption and activation of CO2, thereby enhancing the photocatalytic reduction activity of CO2.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst, its preparation method, and its application. Background Technology

[0002] With the rapid development of human society and the increasing demand for industry, fossil fuels remain the primary source of energy due to the high cost and low adoption rate of new energy sources. This has led to a significant increase in CO2 emissions, placing a burden on the Earth's ecological environment. Current scientific research focuses primarily on developing methods to convert CO2 into valuable chemical products, which is the mainstream research approach. Among the many proposals, the use of solar energy for the catalytic reduction of CO2 shows great potential. However, current photocatalysts for the photocatalytic reduction of CO2 using solar energy have relatively low efficiency, making it difficult to meet human energy needs.

[0003] Nanosheet-like Bi₂WO₆ is widely used in the photocatalytic reduction of CO₂ due to its excellent stability, narrow bandgap, and large specific surface area. However, pure Bi₂WO₆ faces challenges such as low solar energy utilization and high carrier recombination rate. Therefore, constructing heterojunctions and creating crystal defects are effective methods to improve the solar energy utilization of Bi₂WO₆ and reduce electron-hole recombination.

[0004] There are no reports yet of Cu2O-Bi vacancy Bi2WO6 heterojunctions being used as photocatalysts for CO2 reduction. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst, its preparation method, and its applications. This invention constructs a heterojunction by introducing Cu2O-Bi vacancy Bi2WO6, which improves the efficiency of photogenerated electron-hole separation, thereby enhancing photocatalytic activity.

[0006] The technical solution adopted in this invention is: a Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst, containing 10%-30% Cu2O by molar percentage.

[0007] A method for preparing a Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst includes: taking hexadecyltrimethylammonium bromide (CTAB) and CuSO4·5H2O, heating and stirring at 60 ℃-70 ℃ for 20 min-40 min, adding ascorbic acid, continuing to stir at 60 ℃-70 ℃ for 5 min-15 min, adding Bi vacancy Bi2WO6, continuing to stir at 60 ℃-70 ℃ for 5 min-15 min, adjusting the pH value of the resulting mixed solution, finally stirring at 60 ℃-70 ℃ for 5 min-15 min, cooling, centrifuging and washing with deionized water and anhydrous ethanol, and vacuum drying to obtain Cu2O-Bi vacancy Bi2WO6.

[0008] Furthermore, according to the material-liquid ratio, CTAB:CuSO4·5H2O:ascorbic acid:Bi vacancy Bi2WO6 = (1.8 g-5.6 g): (0.03 g-0.12 g): (0.10 g-0.40 g): (0.15 g-0.2 g).

[0009] Further, the pH of the resulting mixed solution is adjusted to 8-10.

[0010] Furthermore, the method for preparing Bi2WO6 with Bi vacancy includes: adding Na2WO4·2H2O, Bi(NO3)3·5H2O and CTAB to deionized water, stirring vigorously, dispersing evenly, and then placing it in a hydrothermal reactor for hydrothermal reaction. After the reaction is completed, washing and vacuum drying are performed to obtain Bi2WO6 with Bi vacancy.

[0011] Furthermore, according to the material-liquid ratio, Na2WO4·2H2O:Bi(NO3)3·5H2O:CTAB:deionized water = (0.8 g-0.9 g): (2.4 g-2.5 g): (0.10 g-0.15 g): (180 mL-220 mL).

[0012] Furthermore, the hydrothermal reaction is carried out at a temperature of 110 ℃-130 ℃ and for a time of 18h-20h.

[0013] The application of the Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst provided by this invention in the photocatalytic reduction of CO2.

[0014] Further, the method is as follows: Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst is added to the photocatalytic reactor, deionized water is injected into the bottom of the photocatalytic reactor, the photocatalytic reactor is evacuated, and then filled with CO2 to carry out photocatalytic reduction of CO2.

[0015] The beneficial effects of this invention are as follows:

[0016] 1. The Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst prepared by the solvothermal method of this invention has a spherical structure and a nanosheet morphology, which increases the specific surface area, improves the carrier separation efficiency, and enhances the photocatalytic activity.

[0017] 2. The Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst prepared by this invention has a stronger ability to absorb visible light, which is an effective method to improve visible light photocatalytic activity.

[0018] 3. The Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst prepared by this invention has good photocatalytic reduction performance of CO2, and the method is simple to prepare, environmentally friendly and non-toxic, low cost, and conducive to large-scale production. Attached Figure Description

[0019] Figure 1 X-ray diffraction patterns of Bi2WO6 heterojunction photocatalysts with Bi vacancies, Cu2O, and Cu2O-Bi2WO6 vacancies.

[0020] Figure 2 Scanning electron microscope images of Bi2WO6 with Bi vacancy (b), Cu2O (a), and Cu2O-Bi2WO6 heterojunction photocatalyst (c).

[0021] Figure 3 Photoluminescence spectra of Bi2WO6 with Bi vacancy, Cu2O, and Cu2O-Bi2WO6 heterojunction photocatalysts.

[0022] Figure 4 The performance of Bi2WO6 with Bi vacancy, Cu2O, and Cu2O-Bi2WO6 heterojunction photocatalysts for the photocatalytic reduction of CO2 to CO is shown in the figure.

[0023] Figure 5 The graph shows the performance of Bi2WO6 with Bi vacancy, Cu2O, and Cu2O-Bi2WO6 heterojunction photocatalysts for the photocatalytic reduction of CO2 to CH4.

[0024] Figure 6 Comparison of photocatalytic reduction rates of CO2 to CO and CH4 by Bi2WO6 with Bi vacancy, Cu2O, and Cu2O-Bi2WO6 heterojunction photocatalysts. Detailed Implementation

[0025] Example 1: Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst.

[0026] I. Preparation Method

[0027] 1. Preparation of Bi2WO6 with Bi vacancy.

[0028] 0.825 g Na2WO4·2H2O, 2.425 g Bi(NO3)3·5H2O and 0.13 g CTAB were added to 200 mL of deionized water and stirred vigorously for 180 min. After the mixture was evenly dispersed, it was placed in a hydrothermal reactor and subjected to a hydrothermal reaction at 120 °C for 18 h. After the reaction was completed, a white precipitate was obtained. The white precipitate was washed three times by centrifugation with deionized water and anhydrous ethanol, and then dried under vacuum at 70 °C to obtain Bi2WO6 with Bi vacancy, which was labeled as BWO.

[0029] 2. Preparation of 10CuO-BWO.

[0030] 1.8225 g CTAB was added to 50 mL of deionized water and stirred for 30 min to disperse it fully. After thorough mixing, 0.0341 g CuSO4·5H2O was added, and the mixture was heated and stirred at 60 °C for 30 min. Then, 0.1228 g ascorbic acid was added, and the mixture was stirred at 60 °C for another 10 min. Then, 0.1571 g Bi vacancy Bi2WO6 was added, and the mixture was stirred at 60 °C for another 10 min. Then, 0.2 mol / L NaOH solution was added dropwise to adjust the pH of the resulting mixed solution to 9. Finally, the mixture was stirred at 60 °C for 10 min. After cooling, the product was washed three times by centrifugation with deionized water and anhydrous ethanol, respectively, and dried under vacuum at 70 °C to obtain a Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst containing 10% Cu2O by molar percentage, labeled as 10CuO-BWO.

[0031] 3. Preparation of 20CuO-BWO.

[0032] 3.645 g CTAB was added to 100 mL of deionized water and stirred for 30 min to disperse it fully. After thorough mixing, 0.0682 g CuSO4·5H2O was added, and the mixture was heated and stirred at 60 °C for 30 min. Then, 0.2455 g ascorbic acid was added, and the mixture was stirred at 60 °C for another 10 min. Then, 0.1571 g Bi vacancy Bi2WO6 was added, and the mixture was stirred at 60 °C for another 10 min. Then, 0.2 mol / L NaOH solution was added dropwise to adjust the pH of the resulting mixed solution to 9. Finally, the mixture was stirred at 60 °C for 10 min. After cooling, the product was washed three times by centrifugation with deionized water and anhydrous ethanol, respectively, and dried under vacuum at 70 °C to obtain a Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst containing 20% ​​Cu2O by molar percentage, labeled as 20CuO-BWO.

[0033] 4. Preparation of 30CuO-BWO.

[0034] 5.4675 g CTAB was added to 150 mL of deionized water and stirred for 30 min to disperse it fully. After thorough mixing, 0.1023 g CuSO4·5H2O was added, and the mixture was heated and stirred at 60 °C for 30 min. Then, 0.3683 g ascorbic acid was added, and the mixture was stirred at 60 °C for another 10 min. Then, 0.1571 g Bi vacancy Bi2WO6 was added, and the mixture was stirred at 60 °C for another 10 min. Then, 0.2 mol-L NaOH solution was added dropwise to adjust the pH of the resulting mixed solution to 9. Finally, the mixture was stirred at 60 °C for 10 min. After cooling, the product was washed three times by centrifugation with deionized water and anhydrous ethanol, respectively, and dried under vacuum at 70 °C to obtain a Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst containing 30% Cu2O by molar percentage, labeled as 30CuO-BWO.

[0035] II. Characterization

[0036] Figure 1 X-ray diffraction (XRD) patterns of Bi2WO6 heterojunction photocatalysts with Bi vacancies, Cu2O, and Cu2O-Bi vacancies. Figure 1 As can be seen, the diffraction characteristic peaks of pure Bi2WO6 and Cu2O correspond one-to-one with the specific standard cards of the material, proving that Bi2WO6 and Cu2O with vacancies were successfully prepared. The comparison between the Cu2O-Bi2WO6 composite sample and the standard cards of pure Bi2WO6 and Cu2O samples shows that the Cu2O-Bi2WO6 composite material provided by this invention has diffraction characteristic peaks of both Bi2WO6 and Cu2O. Moreover, as the content of Cu2O increases, the intensity of the diffraction characteristic peak of Cu2O in the Cu2O-Bi2WO6 composite sample also continuously increases, proving that the Cu2O-Bi2WO6 composite sample was successfully prepared.

[0037] Figure 2 Scanning electron microscope (SEM) images of Bi2WO6 with Bi vacancies, Cu2O, and Cu2O-Bi2WO6 heterojunction photocatalysts. Figure 2 As can be seen in (a), Cu₂O has a nanosphere structure. Figure 2 As can be seen in (b), Bi₂WO₆ with Bi vacancies is mainly composed of nanosheet-like structures, but its surface roughness is due to Bi vacancies. Figure 2 As can be seen in (c), in the Cu2O-Bi vacancy Bi2WO6 composite sample, Cu2O is uniformly distributed on the Bi vacancy Bi2WO6 nanosheets, proving that Cu2O was successfully composited with Bi2WO6.

[0038] Figure 3Photoluminescence spectra (PL) of Bi2WO6 heterojunction photocatalysts with Bi vacancies, Cu2O, and Cu2O-Bi2WO6 vacancies. Figure 3 As can be seen, Bi2WO6 with vacancy has the highest PL emission peak, while Cu2O has the lowest PL emission peak. Furthermore, the PL emission peak of the Cu2O-Bi2WO6 composite sample gradually decreases with the increase of Cu2O. Although the Cu2O-Bi2WO6 composite sample with a Cu2O content of 30% has the lowest PL emission peak among the composite samples and has the advantage of high separation efficiency of photogenerated electron and hole pairs, subsequent photocatalytic performance tests revealed that the Cu2O-Bi2WO6 composite sample with a Cu2O content of 20% has the best photocatalytic reduction performance.

[0039] Example 4: Application of Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst in photocatalytic reduction of CO2.

[0040] At ambient temperature and pressure, 0.05 g of heterojunction photocatalysts of 10CuO-BWO, 20CuO-BWO, and 30CuO-BWO were taken respectively and evenly spread on a ceramic boat. Anhydrous ethanol was then added dropwise, followed by drying to ensure the catalyst was evenly spread on the ceramic boat. The dried ceramic boat was transferred to a photocatalytic reactor. 1 mL of deionized water was injected into the bottom of the photocatalytic reactor (not the surface of the photocatalyst), and the container was sealed with a quartz glass lid. The container was evacuated, and then CO2 was filled into the photocatalytic reactor. This cycle was repeated four times. A 300 W xenon lamp was used as the light source to irradiate the photocatalyst. After every 30 min of irradiation, the upper gas layer was extracted from the container using a microsyringe, and the concentrations of CO and CH4 in the upper gas layer were measured using a gas chromatograph. This was continuously monitored for 2 h.

[0041] Figure 4 Performance diagrams of CO2 reduction to CO for Bi2WO6, Cu2O, and Cu2O-Bi2WO6 heterojunction photocatalysts with Bi vacancies, from... Figure 4 As can be seen, after 2 h of light irradiation, the CO yield of the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 10% reached 22.36 μmol g. -1 The CO yield of the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 20% reached 36.87 μmol g. -1 The CO yield of the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 30% reached 28.11 μmolg. -1 The CO yield of Bi₂WO₆ with Bi vacancy was only 8.28 μmol g. -1 The CO yield of Cu₂O was only 3.13 μmol g.-1 In summary, the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 20% exhibited the highest CO production, thus demonstrating that the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 20% had the best performance in reducing CO2 to CO.

[0042] Figure 5 The graph shows the performance of Bi2WO6 with Bi vacancy, Cu2O, and Cu2O-Bi2WO6 heterojunction photocatalysts in reducing CO2 to CH4. During the redox reaction, CO2 reacts with deionized water in the photocatalytic reactor, producing H2O under illumination. + CH4 was synthesized from Figure 5 As can be seen, after 2 h of light irradiation, the CH4 yield of the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 10% reached 5.12 μmol g. -1 The CH4 yield of the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 20% reached 12.38 μmol g. -1 The CH4 yield of the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 30% reached 7.81 μmol g. -1 The CH4 yield of Bi2WO6 was only 0 μmol g. -1 The CH4 yield of Cu2O was only 0 μmol g. -1 In summary, the Cu2O-Bi2WO6 composite sample with a Cu2O content of 20% exhibited the highest CH4 yield, demonstrating that the Cu2O-Bi2WO6 composite sample with a Cu2O content of 20% had the highest photocatalytic performance.

[0043] The performance comparison of photocatalytic reduction of CO2 to CO by Bi2WO6 with Bi2 vacancies, Cu2O, and Cu2O-Bi2WO6 heterojunction photocatalysts is shown in the figure below. Figure 6 .from Figure 6 As can be seen, the CO generation rate of the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 10% reaches 11.18 μmol h⁻¹. -1 g -1 The CO generation rate of the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 20% reached 18.44 μmol h⁻¹. -1 g -1 The CO generation rate of the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 30% reached 14.06 μmol h⁻¹. -1 g -1The CO generation rate of Bi₂WO₆ with Bi vacancies is only 4.14 μmol / h. -1 g -1 The CO formation rate of Cu2O is only 1.57 μmol / h. -1 g -1 .

[0044] The performance comparison of photocatalytic reduction of CO2 to CH4 by Bi2WO6 with Bi2 vacancy, Cu2O, and Cu2O-Bi2WO6 heterojunction photocatalysts is shown in the figure below. Figure 6 .from Figure 6 As can be seen, the CH4 generation rate of the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 10% reaches 2.56 μmol h⁻¹. -1 g -1 The CH4 generation rate of the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 20% reached 6.19 μmol h⁻¹. -1 g -1 The CH4 generation rate of the Cu2O-Bi vacancy Bi2WO6 composite sample with a Cu2O content of 30% reached 3.91 μmol h⁻¹. -1 g -1 The CH4 generation rate of Bi2WO6 with Bi vacancies is only 0 μmol / h. -1 g -1 The CH4 formation rate of Cu2O is only 0 μmol / h. -1 g -1 .

[0045] In summary, after constructing the Cu2O-Bi vacancy Bi2WO6 heterojunction, this invention improves the photocatalytic reduction of CO2 to CO activity compared to the pure Cu2O and Bi vacancy Bi2WO6 samples, and also increases the yield of the photocatalytic product CH4 through the design of the heterostructure.

Claims

1. The application of a Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst in the photocatalytic reduction of CO2, characterized in that, The method is as follows: Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst is added to the photocatalytic reactor, deionized water is injected into the bottom of the photocatalytic reactor, the photocatalytic reactor is evacuated, and then filled with CO2 to carry out photocatalytic reduction of CO2. The preparation method of Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst is as follows: according to the feed-liquid ratio, CTAB:CuSO4·5H2O:ascorbic acid:Bi vacancy Bi2WO6 = 1.8 g-5.6 g:0.03 g-0.12 g:0.10 g-0.40 g:0.15 g-0.2 g, take CTAB and CuSO4·5H2O, heat and stir at 60 ℃-70 ℃ for 20 min-40 min, then add ascorbic acid, continue stirring at 60 ℃-70 ℃ for 5 min-15 min, then add Bi vacancy Bi2WO6, continue stirring at 60 ℃-70 ℃ for 5 min-15 min, adjust the pH of the resulting mixed solution to 8-10, finally stir at 60 ℃-70 ℃ for 5 min-15 min, cool, centrifuge and wash with deionized water and anhydrous ethanol, and vacuum dry to obtain Cu2O-Bi vacancy Bi2WO6; The method for preparing Bi2WO6 with Bi vacancy includes: adding Na2WO4·2H2O:Bi(NO3)3·5H2O:CTAB:deionized water at a ratio of 0.8 g-0.9 g:2.4 g-2.5 g:0.10 g-0.15 g:180 mL-220 mL to deionized water, stirring vigorously until evenly dispersed, and then placing the mixture in a hydrothermal reactor for hydrothermal reaction at 110 ℃-130 ℃ for 18 h-20 h. After the reaction is completed, the mixture is washed and vacuum dried to obtain Bi2WO6 with Bi vacancy. The Cu2O-Bi vacancy Bi2WO6 heterojunction photocatalyst contains 10%-30% Cu2O by molar percentage.

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