A Na, Sm-CaBi2Nb2O9 / O V Preparation methods and applications of BiOBr piezoelectric photocatalytic materials

Abstract

The application relates to the technical field of piezoelectric photocatalytic materials, in particular to a Na,Sm-CaBi2Nb2O9 / O V -BiOBr piezoelectric photocatalytic material, a preparation method and application thereof. The method comprises the following steps: firstly, preparing Na,Sm-CaBi2Nb2O9 by a molten salt method and dispersing the Na,Sm-CaBi2Nb2O9 in a mannitol solution; then, adding PVP and Bi(NO3)3.5H2O in sequence; and finally, adding a saturated NaBr solution drop by drop and performing hydrothermal treatment; through accurate control of a hydrothermal temperature and a reaction time, a Na,Sm-CaBi2Nb2O9 / O 2+ -BiOBr S-type heterojunction piezoelectric photocatalyst which is rich in oxygen vacancies and has a shared (Bi2O2) V interface is finally obtained. The catalyst realizes the transfer of carrier recombination centers through the electron capture effect of oxygen vacancies, optimizes the local dipole state distribution and the interface non-centrosymmetry, effectively controls the carrier recombination path, significantly enhances the piezoelectric polarization strength, successfully inhibits the self-reduction behavior of the interface Bi 3+ , and greatly improves the piezoelectric photocatalytic activity. The application effectively solves the problems of high crystal face mismatch degree, insufficient stability and low piezoelectric photocatalytic activity of traditional bismuth-based heterojunction materials by constructing structure-matched heterojunction materials, and opens up a new way for the application of layered bismuth-based perovskite materials in the field of piezoelectric photocatalytic water splitting.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric photocatalytic materials technology, and more specifically to a Na,Sm-CaBi2Nb2O9 / O V -BiOBr piezoelectric photocatalytic materials, their preparation methods, and applications. Background Technology

[0002] With the increasing severity of environmental pollution and energy crises worldwide, developing sustainable energy conversion technologies driven by renewable energy sources such as solar energy and environmental kinetic energy has become an important way to alleviate the current ecological crisis. Against this backdrop, piezoelectric photocatalysis technology has attracted much attention due to its unique advantages in clean energy production and the synthesis of high-value-added chemicals. The core mechanism of this technology lies in the fact that piezoelectric materials, under the action of external force, induce deformation of the non-centrosymmetric crystal structure and generate a built-in polarized electric field. This electric field can effectively regulate the directional migration behavior of photogenerated electron-hole pairs and significantly suppress the recombination process of charge carriers.

[0003] In the field of piezoelectric semiconductor catalyst research, Aurivillius-type bismuth-based perovskite materials are distinguished by their unique (Bi2O2) composition. 2+ The alternating ABO3 layered structure has attracted considerable attention. This unique layered structure induces intrinsic structural distortion through interlayer interactions, resulting in excellent carrier separation characteristics under the combined effects of photomechanical energy. Furthermore, Aurivillius-type perovskite materials co-doped with alkali metals and rare earth elements exhibit superior piezoelectric properties and light absorption capabilities. Taking the research of Dou Zhang's group as an example, the co-doping of Na and Sm achieved precise control over the electronic structure of Aurivillius-type CaBi2Nb2O9 materials: Na doping creates empty orbitals in the conduction band, while Sm doping successfully introduces an intermediate energy band. This bimetallic doping strategy not only significantly improves the light absorption efficiency and carrier mobility by enhancing local charge density but also generates an additional piezoelectric field by controlling the phase composition ratio, providing a new approach for optimizing material performance.

[0004] Benefiting from the similar structural characteristics of layered bismuth compounds, Aurivillius-type bismuth-based perovskite materials can form structurally compatible heterojunction systems with other bismuth-based materials. Heterojunction engineering significantly improves material performance by broadening the photoresponse range, optimizing the band structure, establishing efficient electron transport channels, and simultaneously enhancing piezoelectric response characteristics, collectively promoting the efficient separation and migration of photogenerated carriers in Aurivillius-type layered bismuth materials. However, this system faces a key challenge: the surface Bi... 3+It is easily reduced to elemental Bi by photogenerated electrons. This phenomenon leads to the failure of the heterojunction structure, hinders the promotion of photoelectric processes by the piezoelectric effect, and severely limits the further improvement of material performance.

[0005] To address this critical issue, an in-situ hydrothermal method was employed to utilize oxygen-rich vacancies (O2). V BiOBr material was directionally grown on the (00l) crystal plane of Na,Sm-CaBi2Nb2O9 material to construct a structure with a shared interface (Bi2O2). 2+ The structure of Na, Sm-CaBi2Nb2O9 / O V -BiOBr S-type heterojunction system. Under combined optical and ultrasonic excitation, the electron trapping effect of oxygen vacancies promotes the selective enrichment of photogenerated electrons, thereby removing the carrier recombination center from the interface (Bi2O2). 2+ Layer-directed transfer to oxygen vacancies in BiOBr significantly suppresses photogenerated electron pairs at the Bi interface. 3+ Self-reduction. Furthermore, the introduction of oxygen vacancies not only alters the local dipole state distribution of BiOBr but also enhances the non-centrosymmetry of the interface structure by optimizing the local electronic environment of Br atoms at the interface, thereby improving the overall piezoelectric performance of the system. Based on the synergistic regulation of carrier recombination pathways and piezoelectric polarization intensity by oxygen vacancies in the heterojunction system, the piezoelectric photocatalytic activity of the material can be greatly promoted. Summary of the Invention

[0006] The purpose of this invention is to provide a Na, Sm-CaBi2Nb2O9 / O V -BiOBr composite piezoelectric photocatalyst and its preparation method were applied to the piezoelectric photocatalytic decomposition of pure water to produce H2 and H2O2, exhibiting high piezoelectric photocatalytic activity.

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

[0008] A Na, Sm-CaBi2Nb2O9 / O V A method for preparing a BiOBr piezoelectric photocatalyst, characterized in that the method comprises the following steps:

[0009] (1) Disperse an appropriate amount of Na, Sm-CaBi2Nb2O9 and an appropriate amount of PVP in a certain amount of mannitol solution, and then ultrasonically disperse to obtain a white suspension;

[0010] (2) Add an appropriate amount of Bi(NO3)3·5H2O and an appropriate amount of NaBr saturated solution to the above suspension, stir at room temperature, treat the resulting white suspension at a certain temperature, and wash the product with deionized water and ethanol alternately to finally obtain oxygen-rich vacancy and shared (Bi2O2). 2+Na, Sm-CaBi2Nb2O9 / O at the interface V -BiOBr heterojunction piezoelectric photocatalyst;

[0011] In step (1) of this invention, the Na, Sm-CaBi2Nb2O9 is characterized by the following preparation method: weighing Bi2O3, CaCO3, Nb2O5, Na2CO3 and Sm2O3 at room temperature according to stoichiometric ratio, and then adding NaCl / KCl mixed salt as molten salt medium; wherein, the co-doping ratio of Na / Sm is controlled at 1 wt%~5 wt%, and the mass ratio of precursor to molten salt is 1:1; mixing the above raw materials with anhydrous ethanol and grinding for 1 hour, drying and placing in a muffle furnace, calcining at a high temperature of 700~1000 ℃ for 4~8 hours; the obtained product is repeatedly washed with hot deionized water to remove residual salt, and finally obtaining Na, Sm-CaBi2Nb2O9 material with high crystallinity;

[0012] In step (1), 0.1~0.3 g Na, Sm-CaBi2Nb2O9 and 0.3~0.5 g PVP were added to 25 mL of mannitol solution and ultrasonically dispersed for 30 minutes to obtain white suspension A; wherein, the concentration of mannitol solution was 0.05~0.2 M;

[0013] In step (2) of this invention, 0.1~0.5 g of Bi(NO3)3·5H2O is added to the white suspension A obtained in step (1) and stirred continuously for 30 minutes to obtain white suspension B. Then, 3~8 mL of saturated NaBr solution is slowly added dropwise to white suspension B and stirred for 30 minutes to obtain white suspension C. White suspension C is transferred to a Teflon-lined stainless steel hydrothermal reactor and reacted at 120~180 °C for 2~8 hours. The resulting precipitate is washed several times alternately with deionized water and anhydrous ethanol to obtain oxygen-rich vacancy-shared (Bi2O2). 2+ Na, Sm-CaBi2Nb2O9 / O at the interface V -BiOBr heterojunction piezoelectric photocatalyst.

[0014] Furthermore, the present invention also provides a Na, Sm-CaBi2Nb2O9 / O prepared by the aforementioned preparation method. V - Application of BiOBr piezoelectric photocatalyst in piezoelectric photocatalytic pure water splitting.

[0015] Furthermore, 1~20 mg of Na,Sm-CaBi2Nb2O9 / O VBiOBr piezoelectric photocatalyst was ultrasonically dispersed in 50 mL of pure water. N2 or Ar was introduced and the solution was continuously deoxygenated for 30 minutes. The reaction of catalytic pure water decomposition to produce H2 and H2O2 was carried out under a light intensity of 300 W (light source wavelength λ ≥ 420 nm) and an ultrasonic power of 40~250 W.

[0016] The significant advantages of this invention are:

[0017] (1) The Na, Sm-CaBi2Nb2O9 / O prepared in this invention V -The BiOBr piezoelectric photocatalyst uses a combination of molten salt method and hydrothermal method, which reduces the material crystallization temperature and effectively controls the crystal orientation of the material in situ by adjusting the temperature and time of the hydrothermal reaction, thus realizing the construction of shared structural units at the interface.

[0018] (2) The Na, Sm-CaBi2Nb2O9 / O prepared in this invention V -BiOBr piezoelectric photocatalysts have good band matching characteristics and can fully utilize photogenerated carriers through the S-type electron transfer path;

[0019] (3) The Na, Sm-CaBi2Nb2O9 / O prepared in this invention V -BiOBr utilizes interfacial oxygen vacancies to capture photogenerated electrons, precisely confining carrier recombination centers to the electrons captured by oxygen vacancies, effectively avoiding Bi... 3+ The structural failure and performance degradation caused by self-reduction;

[0020] (4) The Na, Sm-CaBi2Nb2O9 / O prepared in this invention V -BiOBr improves the piezoelectricity of the material by introducing oxygen vacancies;

[0021] (5) The Na, Sm-CaBi2Nb2O9 / O prepared by this invention V -BiOBr uses the interface (Bi2O2) 2+ As a carrier transport channel, the introduction of oxygen vacancies effectively modulates the recombination center and piezoelectric polarization intensity of carriers, thus exhibiting excellent piezoelectric photocatalytic pure water decomposition performance. Attached Figure Description

[0022] Figure 1 The CaBi₂Nb₂O₉, Na,Sm-CaBi₂Nb₂O₉, and Na,Sm-CaBi₂Nb₂O₉ / O prepared in Examples 1-4 V X-ray diffraction patterns of BiOBr and Na, Sm-CaBi2Nb2O9 / BiOBr piezoelectric photocatalysts.

[0023] Figure 2 This is a scanning electron microscope image of CaBi2Nb2O9 prepared using Example 1 of this invention.

[0024] Figure 3 This is a scanning electron microscope image of Na, Sm-CaBi2Nb2O9 prepared using Example 2 of this invention.

[0025] Figure 4 The CaBi2Nb2O9 / O prepared using Example 3 of this invention V -Scanning electron microscope image of BiOBr.

[0026] Figure 5 This is a scanning electron microscope image of CaBi2Nb2O9 / BiOBr prepared using Example 4 of this invention.

[0027] Figure 6 The CaBi₂Nb₂O₉, Na,Sm-CaBi₂Nb₂O₉, and Na,Sm-CaBi₂Nb₂O₉ / O₂ prepared in Examples 1-4 of this invention V Piezoelectric photocatalytic H2 production performance of BiOBr and Na, Sm-CaBi2Nb2O9 / BiOBr piezoelectric photocatalysts.

[0028] Figure 7 The CaBi₂Nb₂O₉, Na,Sm-CaBi₂Nb₂O₉, and Na,Sm-CaBi₂Nb₂O₉ / O₂ prepared in Examples 1-4 of this invention V Performance of piezoelectric photocatalytic H2O2 production by BiOBr and Na, Sm-CaBi2Nb2O9 / BiOBr piezoelectric photocatalysts. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0030] Example 1

[0031] A method for preparing a CaBi₂Nb₂O₉ piezoelectric photocatalyst includes the following steps:

[0032] 4.6 g Bi₂O₃, 1.0 g CaCO₃, and 2.65 g Nb₂O₅ were weighed at room temperature according to stoichiometric ratio, and then a NaCl / KCl mixed salt was added as the molten salt medium; the mass ratio of precursor to molten salt was 1:1. The above raw materials were mixed with anhydrous ethanol and ground for 1 hour, dried, and placed in a muffle furnace for calcination at 950 °C for 6 hours. The resulting product was repeatedly washed with hot deionized water to remove residual salt, and finally, highly crystalline CaBi₂Nb₂O₉ material was obtained; its X-ray diffraction pattern is shown below. Figure 1As shown by curve a, its morphology diagram is as follows. Figure 2 As shown.

[0033] The following are application examples of the catalyst prepared in this embodiment for piezoelectric photocatalytic pure water splitting:

[0034] Weigh 10 mg of the above CaBi₂Nb₂O₉ and place it in a quartz reactor containing 50 mL of deionized water. After ultrasonic dispersion for 15 minutes, seal the reactor and introduce Ar to remove oxygen for 30 minutes under magnetic stirring. Perform piezoelectric photocatalytic pure water decomposition tests using a 300 W (λ ≥ 420 nm) Xe lamp as the light source and ultrasonication at 40 kHz and 110 W. Extract 1 mL of gas every 30 minutes and analyze the H₂ yield using gas chromatography. Additionally, every 30 minutes, take 1 mL of the liquid product and react it with KI / H₂. 32 Mo7N6O 28 Liquid ultraviolet analysis was performed after the reaction to obtain the yield of H2O2; the calculated results are shown in [the table below]. Figure 6 and Figure 7 As shown by curve a in the middle.

[0035] Example 2

[0036] A method for preparing a Na,Sm-CaBi2Nb2O9 piezoelectric photocatalyst includes the following steps:

[0037] At room temperature, 4.6 g Bi₂O₃, 1.0 g CaCO₃, 2.65 g Nb₂O₅, 0.02 g Na₂CO₃, and 0.01 g Sm₂O₃ were weighed according to stoichiometric ratios. A NaCl / KCl mixed salt was then added as the molten salt medium; the mass ratio of precursor to molten salt was 1:1. The above raw materials were mixed with anhydrous ethanol and ground for 1 hour, dried, and then calcined in a muffle furnace at 950 °C for 6 hours. The resulting product was repeatedly washed with hot deionized water to remove residual salts, finally yielding a highly crystalline Na,Sm-CaBi₂Nb₂O₉ material. Its X-ray diffraction pattern is shown below. Figure 1 As shown by curve b, its morphology diagram is as follows. Figure 3 As shown.

[0038] The following are application examples of the catalyst prepared in this embodiment for piezoelectric photocatalytic pure water splitting:

[0039] Weigh 10 mg of the above Na, Sm-CaBi2Nb2O9 and place it in a quartz reactor containing 50 mL of deionized water. After ultrasonic dispersion for 15 minutes, seal the reactor and introduce Ar to remove oxygen for 30 minutes under magnetic stirring. Perform piezoelectric photocatalytic pure water decomposition test using a 300 W (λ ≥ 420 nm) Xe lamp as the light source and ultrasonic treatment at 40 kHz and 110 W. Extract 1 mL of gas every 30 minutes and analyze the H2 production using gas chromatography. Additionally, take 1 mL of the liquid product every 30 minutes and react it with KI / H2. 32 Mo7N6O 28 Liquid ultraviolet analysis was performed after the reaction to obtain the yield of H2O2; the calculated results are shown in [the table below]. Figure 6 and Figure 7 As shown by curve b.

[0040] Example 3

[0041] A Na,Sm-CaBi2Nb2O9 / O rich in oxygen vacancies V The preparation method of BiOBr piezoelectric photocatalyst includes the following steps:

[0042] 0.1575 g of Na,Sm-CaBi2Nb2O9 obtained in Example 2 and 0.4 g of PVP were dispersed in 25 mL of 0.1 M mannitol solution and ultrasonically dispersed for 30 minutes to obtain suspension A. 0.194 g of Bi(NO3)3·5H2O was added to white suspension A and stirred continuously for 30 minutes to obtain white suspension B. Then, 4 mL of saturated NaBr solution was slowly added dropwise to white suspension B and stirred for 30 minutes to obtain white suspension C. White suspension C was transferred to a Teflon-lined stainless steel hydrothermal reactor and reacted at 160 °C for 6 hours. The resulting precipitate was washed several times alternately with deionized water and anhydrous ethanol to obtain oxygen-rich vacancy-shared (Bi2O2) precipitate. 2+ Na, Sm-CaBi2Nb2O9 / O at the interface V -BiOBr heterojunction piezoelectric photocatalyst; its X-ray diffraction pattern is as follows Figure 1 As shown by curve c, its morphology diagram is as follows. Figure 4 As shown.

[0043] The following are application examples of the catalyst prepared in this embodiment for piezoelectric photocatalytic pure water splitting:

[0044] Weigh 10 mg of the above Na, Sm-CaBi2Nb2O9 / O VBiOBr was placed in a quartz reactor containing 50 mL of deionized water; after ultrasonic dispersion for 15 minutes, the reactor was sealed, and Ar was introduced for deoxygenation for 30 minutes under magnetic stirring; piezoelectric photocatalytic pure water decomposition was tested using a 300 W (λ≥ 420 nm) Xe lamp as the light source and ultrasonication at 40 kHz and 110 W. 1 mL of gas was extracted every 30 minutes, and the H2 yield was analyzed using gas chromatography; in addition, 1 mL of liquid product was taken every 30 minutes and reacted with KI / H 32 Mo7N6O 28 Liquid ultraviolet analysis was performed after the reaction to obtain the yield of H2O2; the calculated results are shown in [the table below]. Figure 6 and Figure 7 As shown by curve c.

[0045] Example 4

[0046] A method for preparing a Na,Sm-CaBi2Nb2O9 / BiOBr piezoelectric photocatalyst without oxygen vacancies includes the following steps:

[0047] 0.1575 g of Na,Sm-CaBi2Nb2O9 obtained in Example 2 was dispersed in 25 mL of pure water and ultrasonically dispersed for 30 minutes to obtain suspension A. 0.194 g of Bi(NO3)3·5H2O was added to white suspension A and stirred continuously for 30 minutes to obtain white suspension B. Then, 4 mL of saturated NaBr solution was slowly added dropwise to white suspension B and stirred for 30 minutes to obtain white suspension C. White suspension C was transferred to a Teflon-lined stainless steel hydrothermal reactor and reacted at 160 °C for 6 hours. The resulting precipitate was washed several times alternately with deionized water and anhydrous ethanol to obtain a precipitate free of oxygen vacancies and possessing shared (Bi2O2) sites. 2+ The Na, Sm-CaBi2Nb2O9 / BiOBr heterojunction piezoelectric photocatalyst at the interface; its X-ray diffraction pattern is as follows. Figure 1 As shown by curve d, its morphology diagram is as follows. Figure 5 As shown.

[0048] The following are application examples of the catalyst prepared in this embodiment for piezoelectric photocatalytic pure water splitting:

[0049] Weigh 10 mg of the above Na, Sm-CaBi2Nb2O9 / BiOBr and place it in a quartz reactor containing 50 mL of deionized water. After ultrasonic dispersion for 15 minutes, seal the reactor and introduce Ar to remove oxygen for 30 minutes under magnetic stirring. Perform piezoelectric photocatalytic pure water decomposition tests using a 300 W (λ ≥ 420 nm) Xe lamp as the light source and ultrasonication at 40 kHz and 110 W. Extract 1 mL of gas every 30 minutes and analyze the H2 production using gas chromatography. Additionally, every 30 minutes, take 1 mL of the liquid product and react it with KI / H... 32 Mo7N6O 28 Liquid ultraviolet analysis was performed after the reaction to obtain the yield of H2O2; the calculated results are shown in [the table below]. Figure 6 and Figure 7 As shown by curve d in the middle.

[0050] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and these modifications and substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A Na, Sm-CaBi2Nb2O9 / O V The application of BiOBr piezoelectric photocatalyst in piezoelectric photocatalytic pure water splitting is characterized by... The piezoelectric photocatalyst is dispersed in pure water and then deoxygenated by aeration. Subsequently, the pure water is decomposed to produce H2 and H2O2 under the combined action of visible light and ultrasound. The preparation method of the piezoelectric photocatalyst includes the following steps: (1) Disperse an appropriate amount of Na, Sm-CaBi2Nb2O9 and an appropriate amount of PVP in a certain amount of mannitol solution, and then ultrasonically disperse to obtain a white suspension; (2) Add an appropriate amount of Bi(NO3)3·5H2O and an appropriate amount of NaBr saturated solution to the above suspension, stir at room temperature, treat the resulting white suspension at a certain temperature, and wash the product with deionized water and ethanol alternately to finally obtain oxygen-rich vacancy and shared (Bi2O2). 2+ Na, Sm-CaBi2Nb2O9 / O at the interface V -BiOBr heterojunction piezoelectric photocatalyst.

2. The application according to claim 1, characterized in that, In step (1), the preparation method of Na, Sm co-doped CaBi2Nb2O9 includes the following steps: weighing Bi2O3, CaCO3, Nb2O5, Na2CO3 and Sm2O3 at room temperature according to stoichiometric ratio, and then adding NaCl / KCl mixed salt as molten salt medium; wherein, the co-doping ratio of Na / Sm is controlled at 1 wt%~5 wt%, and the mass ratio of Na, Sm-CaBi2Nb2O9 precursor to molten salt is 1:1; mixing the above raw materials with anhydrous ethanol and grinding for 1 hour, drying and placing in a muffle furnace, calcining at a high temperature of 700~1000 ℃ for 4~8 hours; the obtained product is repeatedly washed with hot deionized water to remove residual salt, and finally obtaining highly crystalline Na, Sm-CaBi2Nb2O9 material.

3. The application according to claim 1, characterized in that, In step (1), 0.1~0.3 g of Na, Sm-CaBi2Nb2O9 prepared according to claim 2 and 0.3~0.5 g of PVP are added to 25 mL of mannitol solution and ultrasonically dispersed for 30 minutes to obtain white suspension A; wherein the concentration of mannitol solution is 0.05~0.2 M.

4. The application according to claim 1, characterized in that, In step (2), 0.1~0.5 g Bi(NO3)3·5H2O is added to the white suspension A obtained in step (1) and stirred continuously for 30 minutes to obtain white suspension B. Then, 3~8 mL of saturated NaBr solution is slowly added dropwise to white suspension B and stirred for 30 minutes to obtain white suspension C. White suspension C is transferred to a Teflon-lined stainless steel hydrothermal reactor and reacted at 120~180 ℃ for 2~8 hours. The resulting precipitate is washed several times alternately with deionized water and anhydrous ethanol to obtain oxygen-rich vacancy-shared (Bi2O2). 2+ Na, Sm-CaBi2Nb2O9 / O at the interface V -BiOBr heterojunction piezoelectric photocatalyst.

5. The application according to claim 1, characterized in that, The piezoelectric photocatalyst is used in an amount of 1~20 mg and is ultrasonically dispersed in 50 mL of pure water.

6. The application according to claim 1, characterized in that, The gas used for deoxygenation is N2 or Ar, and the ventilation time is 30 minutes.

7. The application according to claim 1, characterized in that, The wavelength of the light source used in the catalytic reaction is ≥ 420 nm; the ultrasonic power used is 40~250 W.

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