Bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies and preparation and application thereof

Abstract

The application discloses a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies and a preparation and application thereof, and steps include: adding a bismuth source and a molybdenum source into a surfactant aqueous solution in sequence, and carrying out a hydrothermal reaction under a closed condition to obtain the bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies; the surfactant includes one or more of cetyltrimethylammonium bromide and polyvinylpyrrolidone K30; the application selects specific raw materials to construct the bismuth oxide-based heterojunction structure rich in oxygen vacancies in situ through a one-step hydrothermal method, and the prepared catalyst has uniform nanosheet morphology, good dispersity, a large specific surface area, fully exposed active sites and high light absorption efficiency; the synergistic effect of the heterojunction structure and the oxygen vacancies improves the degradation efficiency, the degradation rate of various organic pollutants reaches more than 90%, and the prepared catalyst has excellent cycle stability.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst technology, and in particular to a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies, its preparation and application. Background Technology

[0002] With rapid industrial development, large quantities of organic pollutants such as dyes, antibiotics, and phenols have entered aquatic environments, posing a serious threat to ecosystems and human health. Photocatalysis technology utilizes semiconductor materials to absorb light energy and generate photogenerated electron-hole pairs, oxidizing and decomposing organic pollutants into harmless substances. It boasts advantages such as being green and environmentally friendly, and producing no secondary pollution, making it one of the core technologies in the field of wastewater treatment.

[0003] Among numerous semiconductor materials, bismuth oxide has attracted widespread attention due to its unique layered structure, suitable band gap (approximately 2.1-2.8 eV, exhibiting good response to visible light), and high photocatalytic activity. In particular, its valence band consists of O... 2p and Bi 6s The orbital hybridization of bismuth oxide results in high hole mobility, which is beneficial for oxidation reactions. However, bismuth oxide alone has fatal flaws that severely limit its practical applications: its visible light response range is limited, and photoexcited electrons and holes readily recombine both in bulk and on the surface, leading to a sharp decrease in the number of charge carriers participating in the reaction and low quantum efficiency. Therefore, as a photocatalyst, its degradation efficiency and stability for organic pollutants are insufficient. Currently, constructing heterojunctions (such as Type-II, Z-type, and S-type heterojunctions) using bismuth oxide is an effective means to improve carrier separation efficiency. Through band matching, a built-in electric field is formed at the heterojunction interface, driving electron and hole migration and thus achieving spatial separation and suppressing recombination. However, the drawback of this material is that the heterojunction is not stable enough, and the degradation efficiency and stability of the photocatalyst still need to be improved.

[0004] Therefore, it is essential to provide a bismuth oxide photocatalyst with strong photocatalytic activity and stability. Summary of the Invention

[0005] In view of this, this application provides a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies, its preparation and application, to solve the problem of how to improve the photocatalytic activity and stability of photocatalysts.

[0006] To achieve the above technical objectives, this application adopts the following technical solution: In a first aspect, this application provides a method for preparing a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies, comprising the following steps: A bismuth source and a molybdenum source are added sequentially to an aqueous surfactant solution, and a hydrothermal reaction is carried out under closed conditions to obtain the oxygen-vacancy-rich bismuth oxide-based heterojunction photocatalyst; the surfactant includes one or more of cetyltrimethylammonium bromide and polyvinylpyrrolidone K30.

[0007] Preferably, the bismuth source includes bismuth nitrate.

[0008] Preferably, the molybdenum source comprises molybdate.

[0009] Preferably, the molar ratio of the bismuth source to the molybdenum source is 16-28:6.

[0010] Preferably, the mass ratio of hexadecyltrimethylammonium bromide to bismuth source is 1.4-2.7:16-28.

[0011] Preferably, the hydrothermal reaction temperature is 100-180℃ and the reaction time is 6-48h.

[0012] Preferably, after the hydrothermal reaction, the process further includes the steps of centrifugation, washing, and drying.

[0013] Preferably, the drying temperature is 50-120℃ and the drying time is 6-24h.

[0014] Secondly, this application provides a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies.

[0015] Thirdly, this application provides the application of a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies in the degradation of organic pollutants.

[0016] The beneficial effects of this application are as follows: This application selects specific raw materials to construct an oxygen-vacancy-rich bismuth oxide-based heterojunction structure in situ through a one-step hydrothermal method. The resulting catalyst nanosheets have uniform morphology, good dispersibility, large specific surface area, fully exposed active sites, and high light absorption efficiency. The synergistic effect of the heterojunction structure and oxygen vacancies significantly broadens the visible light response range, effectively inhibits photogenerated carrier recombination, and improves degradation efficiency. The degradation rate of various organic pollutants reaches more than 90%, and the obtained catalyst has excellent cycle stability. After multiple cycles of degradation, the activity decay is not obvious, and the chemical stability is good. It is not easy to undergo structural collapse, which is beneficial to the stability of the photocatalyst. Attached Figure Description

[0017] Figure 1 XRD patterns of the catalysts obtained in Examples 1, 2 and Comparative Example 1; Figure 2 SEM images of the catalyst obtained in Example 1; Figure 3 The EPR spectra of the catalysts obtained in Example 2 and Comparative Example 1 are shown below. Figure 4 The graphs show the performance of the catalysts obtained in Examples 1-4 under simulated visible light for photocatalytic degradation of tetracycline hydrochloride. Figure 5 This is a simulated visible light photocatalytic degradation performance curve of the catalyst obtained in Example 2 for different organic pollutants. Figure 6 This is a graph showing the photocatalytic degradation performance of tetracycline hydrochloride by the catalyst obtained in Example 2 under natural light. Figure 7 The graphs show the performance of the catalysts obtained in Example 2 and Comparative Examples 1-3 under simulated visible light for photocatalytic degradation of tetracycline hydrochloride. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] This application provides a method for preparing a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies, comprising the following steps: A bismuth source and a molybdenum source are added sequentially to an aqueous surfactant solution, and a hydrothermal reaction is carried out under closed conditions to obtain the oxygen-vacancy-rich bismuth oxide-based heterojunction photocatalyst; the surfactant includes one or more of cetyltrimethylammonium bromide and polyvinylpyrrolidone K30.

[0020] This application selects specific raw materials to construct an oxygen-vacancy-rich bismuth oxide-based heterojunction structure in situ using a one-step hydrothermal method. The oxygen vacancies enhance the adsorption of pollutants and the absorption of visible light, while the built-in electric field formed at the heterojunction interface effectively suppresses electron-hole recombination, thereby significantly improving the photocatalytic degradation efficiency and stability.

[0021] Specifically, by combining bismuth and molybdenum sources to construct a heterojunction in situ, the two sources achieve bandgap matching, creating a built-in electric field at the heterojunction interface. This drives electron and hole migration, achieving spatial separation and enabling efficient and stable degradation of various organic pollutants. Under the influence of the molybdenum source and surfactants, the final product can form oxygen vacancies, enhancing oxygen adsorption and promoting carrier separation, thereby significantly improving reactive oxygen species (ROS). O2 - and The generation of OH and the overall photocatalytic performance.

[0022] It is worth noting that this application selects a specific substance as a surfactant to regulate the morphology, control the size and dispersibility of the nanosheets, increase the specific surface area and the exposure of active sites, which can induce the bismuth oxide-based complex to grow into a sheet-like structure, reduce the aggregation of active sites, ensure the uniformity of the morphology of the subsequent nanosheets, and use a one-step hydrothermal reaction method to construct the product in situ. The oxygen vacancy distribution is uniform and will not be excessively reduced to generate metallic bismuth, avoiding the destruction of the material structure. This overcomes the contradiction that the uniform distribution of oxygen vacancy and the stability of the heterojunction structure cannot be achieved at the same time. The resulting photocatalyst has high photocatalytic activity and stability.

[0023] In some embodiments, the bismuth source includes bismuth nitrate.

[0024] In this embodiment, the role of the bismuth source is to provide Bi 3+ The ion is a raw material for forming the bismuth oxygen structural unit in bismuth molybdate. Its nitrate ion NO3... - They are usually treated as counterions, removed during the reaction or involved in acid-base regulation, and do not enter the final crystal lattice.

[0025] In some embodiments, bismuth chloride (BiCl3) can also be used as a bismuth source, but it is highly hydrolyzable and easily forms basic salts, requiring strict control of pH and water content.

[0026] In some embodiments, the molybdenum source comprises molybdate.

[0027] In this embodiment, the molybdenum source serves to provide MoO4. 2- Ions, with Bi 3+ Condensation or precipitation reactions occur, and the construction of the Bi-O-Mo bonded network is the source of the molybdenum-oxygen structural units in bismuth molybdate.

[0028] In some embodiments, the molar ratio of the bismuth source to the molybdenum source is 16-28:6.

[0029] In this embodiment, if the molar ratio is too high, stable bismuth molybdate will not form; if the molar ratio is too low, bismuth vacancies will form. This affects the formation of heterojunctions and oxygen vacancies.

[0030] In some embodiments, the molar ratio of hexadecyltrimethylammonium bromide to bismuth source is 1.4-2.7:16-28.

[0031] In this embodiment, if the molar ratio is too high or too low, it will directly affect the formation of the sheet-like morphology, resulting in a loose heterojunction.

[0032] In some embodiments, the amount of CTAB used is 0.05-0.3 g, the amount of deionized water used is 50-100 mL, the mass of bismuth nitrate pentahydrate is 0.5-3 g, and the mass of sodium molybdate dihydrate is 0.1-0.5 g.

[0033] In some embodiments, the hydrothermal reaction temperature is 100-180°C and the reaction time is 6-48 hours.

[0034] In some embodiments, after the hydrothermal reaction, the steps further include: centrifugation and washing / drying.

[0035] In some embodiments, the drying temperature is 50-120°C and the drying time is 6-24 hours.

[0036] Specifically, the preparation method of the bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies in this application is as follows: The surfactant was added to deionized water and stirred at room temperature until completely dissolved to form a homogeneous surfactant aqueous solution. A bismuth source was added to the surfactant aqueous solution and dissolved completely by sonication. Then, a molybdenum source was added and dissolved by sonication. The solution was then stirred on a magnetic stirrer to form a mixed precursor solution. The mixed precursor solution was transferred to a high-pressure reactor lined with polytetrafluoroethylene (PTFE) with a filling degree of 60%-80%. After sealing, the reactor was placed in a forced-air drying oven for reaction. After the reaction was completed, the reactor was naturally cooled to room temperature. The precipitate was collected by centrifugation and washed with water and ethanol in sequence to remove impurities. Finally, the washed product was dried in an oven to obtain a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies.

[0037] This application provides a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies.

[0038] In this application, the heterojunction structure is an S-type heterojunction. Type II and Z-type heterojunctions have relatively low carrier separation efficiency. The S-type heterojunction, through interfacial recombination of weak electrons and weak holes, retains strong reducing electrons and strong oxidizing holes, and simultaneously, in synergy with oxygen vacancies, further enhances separation efficiency and surface reactivity. This significantly improves visible light absorption and photogenerated carrier separation efficiency, demonstrating significant advantages in the degradation of various organic pollutants such as Rhodamine B, tetracycline, and ciprofloxacin.

[0039] The synergistic mechanism between oxygen vacancies and heterojunction structures is as follows: Oxygen vacancies can trap photogenerated electrons, further suppressing bulk recombination, while the S-shaped interfacial electric field drives cross-interfacial recombination, thus improving separation efficiency through a dual-pathway approach. Oxygen vacancies provide adsorption / activation sites, synergizing with the strong oxidation holes or strong reduction electrons retained in the S-shaped heterojunction to increase the oxidation / reduction reaction rate. Oxygen vacancies can also modulate the valence and conduction band positions of semiconductors, making the S-shaped band bending more pronounced and enhancing interfacial recombination efficiency.

[0040] This application provides the application of an oxygen-vacancy-rich bismuth oxide-based heterojunction photocatalyst in the degradation of organic pollutants. Organic pollutants include, but are not limited to, organic dyes, antibiotics, and phenolic compounds.

[0041] The following specific embodiments further illustrate this solution.

[0042] Example 1 A method for preparing a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies, comprising the following steps: 0.2 g CTAB was dissolved in 80 mL of deionized water and stirred at room temperature for 15 min to ensure complete dissolution, thus obtaining an aqueous solution of the activator. Subsequently, 1 g bismuth nitrate pentahydrate and 0.15 g sodium molybdate dihydrate were added to the solution sequentially. The solution was first sonicated for 40 min to dissolve, and then magnetically stirred for 2 h to form a homogeneous mixed precursor solution. The resulting mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene, sealed, and placed in an electric thermostatic drying oven at 150 °C for 12 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature, and the product was collected by centrifugation at 10000 r / min for 5 min. The product was then washed three times alternately with deionized water and anhydrous ethanol. Finally, the washed product was dried in a vacuum drying oven at 60 °C for 20 h and then ground to obtain a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies.

[0043] Example 2 A method for preparing a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies, comprising the following steps: 0.2 g CTAB was dissolved in 80 mL of deionized water and stirred at room temperature for 15 min to ensure complete dissolution, thus obtaining an aqueous solution of the activator. Subsequently, 1.2 g bismuth nitrate pentahydrate and 0.15 g sodium molybdate dihydrate were added to the solution sequentially. The solution was first sonicated for 40 min to dissolve, and then magnetically stirred for 2 h to form a homogeneous mixed precursor solution. The resulting mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene, sealed, and placed in an electric thermostatic drying oven at 150 °C for 12 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature, and the product was collected by centrifugation at 10000 r / min for 5 min. The product was then washed three times alternately with deionized water and anhydrous ethanol. Finally, the washed product was dried in a vacuum drying oven at 60 °C for 20 h and then ground to obtain a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies.

[0044] Example 3 A method for preparing a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies, comprising the following steps: 0.1 g CTAB was dissolved in 80 mL of deionized water and stirred at room temperature for 15 min to ensure complete dissolution, thus obtaining an aqueous solution of the activator. Subsequently, 1 g bismuth nitrate pentahydrate and 0.15 g sodium molybdate dihydrate were added to the solution sequentially. The solution was first sonicated for 40 min to dissolve, and then magnetically stirred for 2 h to form a homogeneous mixed precursor solution. The resulting mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene, sealed, and placed in an electric thermostatic drying oven at 150 °C for 12 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature, and the product was collected by centrifugation at 10000 r / min for 5 min. The product was then washed three times alternately with deionized water and anhydrous ethanol. Finally, the washed product was dried in a vacuum drying oven at 60 °C for 20 h and then ground to obtain a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies.

[0045] Example 4 A method for preparing a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies, comprising the following steps: 0.2 g CTAB was dissolved in 80 mL of deionized water and stirred at room temperature for 15 min to ensure complete dissolution, thus obtaining an aqueous solution of the activator. Subsequently, 1 g bismuth nitrate pentahydrate and 0.15 g sodium molybdate dihydrate were added to the solution sequentially. The solution was first sonicated for 40 min to dissolve, and then magnetically stirred for 2 h to form a homogeneous mixed precursor solution. The resulting mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene, sealed, and placed in an electric thermostatic drying oven at 120 °C for 12 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature, and the product was collected by centrifugation at 10000 r / min for 5 min. The product was then washed three times alternately with deionized water and anhydrous ethanol. Finally, the washed product was dried in a vacuum drying oven at 60 °C for 20 h. After grinding, a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies was obtained.

[0046] Comparative Example 1 A method for preparing a photocatalyst is the same as in Example 2, except that sodium molybdate dihydrate is not included, and the product prepared is bismuth oxide photocatalyst.

[0047] Comparative Example 2 A method for preparing a photocatalyst is the same as in Example 2, except that the addition of the surfactant CTAB is not included, and the resulting product is a bismuth oxide-based heterojunction photocatalyst without oxygen vacancies.

[0048] Comparative Example 3 A method for preparing a photocatalyst is the same as in Example 2, except that the molar ratio of bismuth nitrate pentahydrate to sodium molybdate dihydrate is 2:1, and the resulting product is a bismuth molybdate photocatalyst.

[0049] Testing and Evaluation The structure of the prepared photocatalyst was identified. Figure 1 As shown, in the XRD patterns of Examples 1, 2 and Comparative Example 1, the bismuth oxide-based photocatalyst exhibits distinct characteristic peaks at 28.3°, 32.5°, 46.7° and 55.5°, indicating that the composite contains bismuth oxide. Figure 2 The image shown is an SEM image of Example 1, which shows that the composite catalyst has a plate-like morphology, with the small-sized plate-like structures belonging to bismuth oxide. Figure 3 The EPR spectra of the catalysts obtained in Example 2 and Comparative Example 1 are shown. Clear paramagnetic resonance signals were observed during the tests, clearly confirming the presence of oxygen vacancies. The results indicate that the vacancy concentration of the composite catalyst is significantly higher than that of the pure sample, and that oxygen vacancies have a direct impact on photocatalytic performance.

[0050] The photocatalytic performance was tested under simulated visible light (wavelength > 420 nm) irradiation. Figure 4 The graphs show the performance of the catalysts obtained in Examples 1-4 under simulated visible light for photocatalytic degradation of tetracycline hydrochloride.

[0051] Figure 5 The graph shows the performance curves of the catalyst obtained in Example 2 under simulated visible light for photocatalytic degradation of different organic pollutants. Figure 6 This is a graph showing the performance of the catalyst obtained in Example 2 in the photocatalytic degradation of tetracycline hydrochloride under natural light. Figure 7 The graphs show the performance of the catalysts obtained in Example 2 and Comparative Examples 1-3 under simulated visible light for photocatalytic degradation of tetracycline hydrochloride.

[0052] like Figure 5 As shown, the bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies was used to degrade tetracycline at an initial concentration of 10 mg / L (catalyst dosage 0.2 g / L), and the degradation rate of tetracycline reached over 84% within 100 min. Figure 6 The results showed that the catalyst achieved a degradation rate of 91.1%-95.3% for ciprofloxacin, tetracycline, and norfloxacin within 100 min. Under natural light irradiation (… Figure 6 The catalyst achieved a degradation rate of 95%-100% for ciprofloxacin, tetracycline, norfloxacin, and rhodamine B. In the comparative examples, the sample without sodium molybdate dihydrate was a bismuth oxide photocatalyst; the sample with a molar ratio of bismuth nitrate pentahydrate to sodium molybdate dihydrate of 2:1 was a Bi₂MoO₆ photocatalyst. Due to the higher carrier recombination efficiency of single semiconductors, their photocatalytic degradation activity for pollutants is significantly lower than that of bismuth oxide heterojunction catalysts. The relevant photocatalytic degradation efficiency test results are as follows: Figure 7 As shown.

[0053] In summary, this application presents a photocatalyst prepared in situ via a one-step method using specific raw materials, achieving a synergistic effect of heterojunction construction and the introduction of abundant oxygen vacancies. The heterojunction structure effectively suppresses electron-hole pair recombination, while the abundant oxygen vacancies not only broaden the photoresponse range but also provide numerous active sites for the adsorption and activation of reactant molecules, significantly improving the separation efficiency of photogenerated carriers and the interfacial reaction activity. These results demonstrate that this catalyst exhibits excellent photocatalytic activity and stability in the degradation of organic pollutants, and its performance is significantly superior to that of bismuth oxide alone or comparative samples without introduced oxygen vacancies.

[0054] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies, characterized in that, Includes the following steps: Bismuth source and molybdenum source are added sequentially to an aqueous surfactant solution, and a hydrothermal reaction is carried out under closed conditions to obtain the oxygen-vacancy-rich bismuth oxide-based heterojunction photocatalyst. The surfactant includes one or more of cetyltrimethylammonium bromide and polyvinylpyrrolidone K30.

2. The preparation method according to claim 1, characterized in that, The bismuth source includes bismuth nitrate.

3. The preparation method according to claim 1, characterized in that, The molybdenum source includes molybdate.

4. The preparation method according to claim 1, characterized in that, The molar ratio of the bismuth source to the molybdenum source is 16-28:

6.

5. The preparation method according to claim 1, characterized in that, The molar ratio of hexadecyltrimethylammonium bromide to bismuth source is 1.4-2.7:16-28.

6. The preparation method according to claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 100-180℃ for a time of 6-48 hours.

7. The preparation method according to claim 1, characterized in that, After the hydrothermal reaction, the process also includes the steps of centrifugation, washing, and drying.

8. The preparation method according to claim 1, characterized in that, The drying temperature is 50-120℃, and the drying time is 6-24h.

9. A bismuth oxide-based heterojunction photocatalyst rich in oxygen vacancies obtained by the preparation method according to any one of claims 1-8.

10. The application of the oxygen-vacancy-rich bismuth oxide-based heterojunction photocatalyst as described in claim 9 in the degradation of organic pollutants.

Images