Preparation method and application of Na, Sm-CaBi2Nb2O9 / OV-BiOBr piezoelectric photocatalytic material

Abstract

The invention relates to the technical field of piezoelectric electro-catalytic materials, in particular to a Na, Sm-CaBi2Nb2O9 / OV-BiOBr piezoelectric electro-catalytic material as well as a preparation method and application of the Na, Sm-CaBi2Nb2O9 / OV-BiOBr piezoelectric electro-catalytic material. The method comprises the following steps: firstly, preparing Na and Sm-CaBi2Nb2O9 by adopting a molten salt method, dispersing the Na and the Sm-CaBi2Nb2O9 into a mannitol solution, then sequentially adding PVP and Bi (NO3) 3.5 H2O, and dropwise adding a saturated NaBr solution for hydrothermal treatment; the Na, Sm-CaBi2Nb2O9 / OV-BiOBr S type heterojunction piezoelectric photocatalyst which is rich in oxygen vacancies and has a shared (Bi2O2) < 2 + > interface is finally obtained by accurately regulating and controlling the hydrothermal temperature and the reaction time. According to the catalyst, transfer of a carrier recombination center is achieved through the electron capture effect of oxygen vacancies, local dipole state distribution and non-central symmetry of an interface are optimized, and the piezoelectric polarization intensity is remarkably enhanced while a carrier recombination path is effectively regulated and controlled; therefore, the self-reduction behavior of the interface Bi < 3 + > is successfully inhibited, and the piezoelectric electro-catalytic activity is greatly improved. By constructing the heterojunction material with a matched structure, the problems of high crystal face mismatching degree, insufficient stability, relatively low piezoelectric electro-catalytic activity and the like of a traditional bismuth-based heterojunction material are effectively solved, and a new way is opened up for application of the layered bismuth-based perovskite material in the field of piezoelectric electro-catalytic water decomposition.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric photocatalytic materials, and more particularly to a Na, Sm-CaBi2Nb2O9 / O V -BiOBr piezoelectric photocatalytic material and its preparation method and application. Background Art

[0002] With the increasingly severe problems of environmental pollution and energy crisis globally, the development of 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. In this context, piezoelectric photocatalysis technology has attracted much attention due to its unique advantages in the fields of clean energy preparation and synthesis of high-value chemicals. The core mechanism of this technology is that under the action of external force, piezoelectric materials induce deformation of the non-centrosymmetric crystal structure and generate an internal built-in polarization electric field, which can effectively regulate the directional migration behavior of photo-generated electron-hole pairs and significantly inhibit the carrier recombination process.

[0003] In the research field of piezoelectric semiconductor catalysts, Aurivillius-type bismuth-based perovskite materials have attracted much attention due to their unique (Bi2O2) 2+ / ABO3 layer alternating arrangement structure. This special layered structure induces intrinsic structural distortion through interlayer interactions, enabling it to exhibit excellent carrier separation characteristics under the combined action of light and mechanical energy. In addition, Aurivillius-type perovskite materials co-doped with alkali metals and rare earth elements exhibit more excellent piezoelectric properties and light absorption ability. Taking the research of the Dou Zhang group as an example, the co-doping of Na and Sm realizes the fine regulation of the electronic structure of the Aurivillius-type CaBi2Nb2O9 material: Na doping forms empty orbitals in the conduction band, while Sm doping successfully introduces an intermediate energy band. This dual-metal doping strategy not only significantly improves the light absorption efficiency and carrier mobility of the material by enhancing the local charge density, but also generates an additional piezoelectric field by regulating the phase composition ratio, providing a new way for the optimization of material properties.

[0004] Benefiting from the similar structural characteristics of layered bismuth compounds, Aurivillius-type bismuth-based perovskite materials can construct a structure-matched heterojunction system with other bismuth-based materials. Heterojunction engineering significantly improves the material properties by broadening the light response range, optimizing the energy band structure, establishing an efficient electron transport channel and simultaneously enhancing the piezoelectric response characteristics, jointly promoting the efficient separation and migration of photo-generated carriers in Aurivillius-type layered bismuth-based materials. However, there is a key challenge in this system: Bi on the material surface 3+It is easily reduced to Bi element by photogenerated electrons. This phenomenon will cause the heterojunction structure to fail, hinder the promotion of the piezoelectric effect on the photoelectric process, and seriously limit the further improvement of material performance.

[0005] To solve this key problem, an in-situ hydrothermal method was used to convert oxygen vacancies (O V ) BiOBr material is directionally grown on the (00l) crystal plane of Na, Sm-CaBi2Nb2O9 material to construct a shared interface (Bi2O2) 2+ Na, Sm-CaBi2Nb2O9 / O V -BiOBr S-type heterojunction system. Under the conditions of combined light and ultrasound excitation, the electron capture effect of oxygen vacancies promotes the selective enrichment of photogenerated electrons, thereby moving the carrier recombination center from the interface (Bi2O2) to the 2+ The layer is directional transferred to the oxygen vacancies of BiOBr, which significantly inhibits the photogenerated electrons from reacting with the interfacial Bi 3+ Furthermore, the introduction of oxygen vacancies not only modifies the local dipole state distribution of BiOBr but also further enhances the non-centrosymmetry of the interface structure by optimizing the local electronic environment of the interfacial Br atoms, thereby improving the overall piezoelectric performance of the system. The synergistic regulation of carrier recombination pathways and piezoelectric polarization strength by oxygen vacancies in heterojunction systems can significantly enhance the piezoelectric photocatalytic activity of the material. Summary of the Invention

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

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

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

[0009] (1) Disperse appropriate amounts of Na, Sm-CaBi2Nb2O9 and PVP in a certain amount of mannitol solution, and obtain a white suspension by ultrasonic dispersion;

[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 resulting product alternately with deionized water and ethanol to obtain a product rich in oxygen vacancies and having shared (Bi2O2) 2+Na, Sm-CaBi2Nb2O9 / O interface V -BiOBr heterojunction piezoelectric photocatalyst;

[0011] In step (1) of the present invention, for the Na, Sm-CaBi2Nb2O9 mentioned, its preparation method includes the following steps: Weigh Bi2O3, CaCO3, Nb2O5, Na2CO3 and Sm2O3 according to stoichiometric ratio at room temperature, and then add a NaCl / KCl mixed salt as a molten salt medium; among them, the co-doping ratio of Na / Sm is controlled at 1 wt% - 5 wt%, and the mass ratio of the precursor to the molten salt is 1:1; Mix the above raw materials with absolute ethanol and grind them together for 1 hour, dry them and place them in a muffle furnace, and calcine them at a high temperature of 700 - 1000 °C for 4 - 8 hours; The obtained product is repeatedly washed with hot deionized water to remove residual salts, and finally a high-crystallinity Na, Sm-CaBi2Nb2O9 material is obtained;

[0012] In step (1), add 0.1 - 0.3 g of Na, Sm-CaBi2Nb2O9 and 0.3 - 0.5 g of PVP to 25 mL of mannitol solution, and ultrasonically disperse for 30 minutes to obtain a white suspension A; among them, the concentration of the mannitol solution is 0.05 - 0.2 M;

[0013] In step (2) of the present invention, add 0.1 - 0.5 g of Bi(NO3)3·5H2O to the white suspension A described in step (1) and continuously stir for 30 minutes to obtain a white suspension B, then slowly drip 3 - 8 mL of saturated NaBr solution into the white suspension B and stir for 30 minutes to obtain a white suspension C; Transfer the white suspension C into a stainless steel hydrothermal autoclave lined with Teflon, and react at 120 - 180 °C for 2 - 8 hours; The obtained precipitate is washed alternately with deionized water and absolute ethanol several times to obtain a Na, Sm-CaBi2Nb2O9 / O 2+ Na, Sm-CaBi2Nb2O9 / O interface V -BiOBr heterojunction piezoelectric photocatalyst.

[0014] In addition, the present invention also provides an application of the Na, Sm-CaBi2Nb2O9 / O V -BiOBr piezoelectric photocatalyst prepared by the said preparation method in piezoelectric photocatalytic pure water decomposition.

[0015] Furthermore, add 1 - 20 mg of Na, Sm-CaBi2Nb2O9 / O V- The BiOBr piezoelectric photocatalyst was ultrasonically dispersed in 50 mL of pure water. N2 or Ar was introduced and maintained for 30 minutes to fully deoxygenate the solution. The catalytic reaction for the decomposition of pure water 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 remarkable advantages of the present invention are as follows:

[0017] (1) The molten salt method combined with the hydrothermal method used for preparing the Na, Sm-CaBi2Nb2O9 / O V -BiOBr piezoelectric photocatalyst can reduce the crystallization temperature of the material and effectively regulate the crystal plane orientation of in-situ growth of the material by controlling the temperature and time of the hydrothermal reaction, realizing the construction of an interface-sharing structural unit;

[0018] (2) The Na, Sm-CaBi2Nb2O9 / O V -BiOBr piezoelectric photocatalyst prepared in the present invention has good energy band matching characteristics and can fully utilize photo-generated carriers according to the S-type electron transfer path;

[0019] (3) The Na, Sm-CaBi2Nb2O9 / O V -BiOBr prepared in the present invention realizes the capture of photo-generated electrons by using interface oxygen vacancies, and can accurately limit the carrier recombination center at the electrons captured by the oxygen vacancies, effectively avoiding the structural failure and performance degradation problems caused by the self-reduction of Bi 3+ ;

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

[0021] (5) The Na, Sm-CaBi2Nb2O9 / O V -BiOBr uses the interface (Bi2O2) 2+ as the carrier transport channel, and effectively regulates the carrier recombination center and the intensity of piezoelectric polarization by introducing oxygen vacancies, thereby exhibiting excellent piezoelectric photocatalytic performance for the decomposition of pure water. Description of the Drawings

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

[0023] Figure 2 It is the scanning electron microscope image of CaBi2Nb2O9 prepared in Example 1 of the present invention.

[0024] Figure 3 It is the scanning electron microscope image of Na, Sm-CaBi2Nb2O9 prepared in Example 2 of the present invention.

[0025] Figure 4 It is the scanning electron microscope image of CaBi2Nb2O9 / O V -BiOBr prepared in Example 3 of the present invention.

[0026] Figure 5 It is the scanning electron microscope image of CaBi2Nb2O9 / BiOBr prepared in Example 4 of the present invention.

[0027] Figure 6 It is the piezoelectric photocatalytic H2 production performance diagram of CaBi2Nb2O9, Na, Sm-CaBi2Nb2O9, Na, Sm-CaBi2Nb2O9 / O V -BiOBr and Na, Sm-CaBi2Nb2O9 / BiOBr piezoelectric photocatalysts prepared in Examples 1-4 of the present invention.

[0028] Figure 7 It is the piezoelectric photocatalytic H2O2 production performance diagram of CaBi2Nb2O9, Na, Sm-CaBi2Nb2O9, Na, Sm-CaBi2Nb2O9 / O V -BiOBr and Na, Sm-CaBi2Nb2O9 / BiOBr piezoelectric photocatalysts prepared in Examples 1-4 of the present invention. Detailed implementation manners

[0029] The following further describes the content of the present invention in detail in conjunction with the accompanying drawings and specific embodiments:

[0030] Example 1

[0031] A preparation method of a CaBi2Nb2O9 piezoelectric photocatalyst includes the following steps:

[0032] Weigh 4.6 g of Bi2O3, 1.0 g of CaCO3 and 2.65 g of Nb2O5 according to the stoichiometric ratio at room temperature, and then add a NaCl / KCl mixed salt as a molten salt medium; wherein, the mass ratio of the precursor to the molten salt is 1:1; mix the above raw materials with absolute ethanol and grind them together for 1 hour, dry them and place them in a muffle furnace, and calcine them at a high temperature of 950 °C for 6 hours; the obtained product is repeatedly washed with hot deionized water to remove the residual salts, and finally a CaBi2Nb2O9 material with high crystallinity is obtained; its X-ray diffraction pattern is as Figure 1As shown by curve a in the figure, its morphology diagram is as Figure 2 shown.

[0033] The following gives an application example of using the catalyst prepared in this example for piezoelectric photocatalytic pure water decomposition:

[0034] Weigh 10 mg of the above-mentioned CaBi2Nb2O9 and place it in a quartz reactor containing 50 mL of deionized water; after ultrasonic dispersion for 15 minutes, seal the reactor, and purge with Ar for 30 minutes under magnetic stirring; use a 300 W (λ ≥ 420 nm) Xe lamp as the light source, and perform piezoelectric photocatalytic pure water decomposition test under the ultrasonic action of 40 kHz and 110 W. Extract 1 mL of gas every 30 minutes, and analyze the H2 production using gas chromatography; in addition, take 1 mL of liquid product every 30 minutes and mix it with KI / H 32 Mo7N6O 28 Perform liquid ultraviolet analysis after the reaction to obtain the production of H2O2; the calculated results are shown in Figure 6 and Figure 7 as shown by curve a in the figure.

[0035] Example Two

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

[0037] Weigh 4.6 g of Bi2O3, 1.0 g of CaCO3, 2.65 g of Nb2O5, 0.02 g of Na2CO3 and 0.01 g of Sm2O3 according to the stoichiometric ratio at room temperature, and then add a NaCl / KCl mixed salt as a molten salt medium; among them, the mass ratio of the precursor to the molten salt is 1:1; mix and grind the above raw materials with absolute ethanol for 1 hour, dry and place them in a muffle furnace, and calcine at 950 °C for 6 hours; the obtained product is repeatedly washed with hot deionized water to remove the residual salts, and finally a high-crystallinity Na, Sm-CaBi2Nb2O9 material is obtained; its X-ray diffraction pattern is as Figure 1 shown by curve b in the figure, and its morphology diagram is as Figure 3 shown.

[0038] The following gives an application example of using the catalyst prepared in this example for piezoelectric photocatalytic pure water decomposition:

[0039] Weigh 10 mg of the above-mentioned 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 purge with Ar for 30 minutes under magnetic stirring; use a 300 W (λ ≥ 420nm) Xe lamp as the light source, and perform piezophotocatalytic pure water decomposition test under the ultrasonic action of 40 kHz and 110 W. Extract 1 mL of gas every 30 minutes, and analyze the H2 production using gas chromatography; in addition, take 1 mL of the liquid product every 30 minutes and mix it with KI / H 32 Mo7N6O 28 After the reaction, perform liquid UV analysis to obtain the production of H2O2; the calculated results are shown in Figure 6 and Figure 7 the curve b shown in

[0040] Example 3

[0041] A preparation method of an oxygen vacancy-rich Na, Sm-CaBi2Nb2O9 / O V -BiOBr piezophotocatalyst, comprising the following steps:

[0042] Take 0.1575 g of the Na, Sm-CaBi2Nb2O9 obtained in Example 2 and 0.4 g of PVP and disperse them in 25 mL of a mannitol solution with a concentration of 0.1 M. After ultrasonic dispersion for 30 minutes, obtain suspension A; add 0.194 g of Bi(NO3)3·5H2O to the white suspension A and continuously stir for 30 minutes to obtain white suspension B, then slowly drop 4 mL of saturated NaBr solution into the white suspension B and stir for 30 minutes to obtain white suspension C; transfer the white suspension C into a stainless steel hydrothermal autoclave with a Teflon lining and react at 160 °C for 6 hours; wash the obtained precipitate several times alternately with deionized water and absolute ethanol to obtain an oxygen vacancy-rich Na, Sm-CaBi2Nb2O9 / O with a shared (Bi2O2) 2+ interface Na, Sm-CaBi2Nb2O9 / O V -BiOBr heterojunction piezophotocatalyst; its X-ray diffraction pattern is as shown in Figure 1 the curve c shown in Figure 4 shown.

[0043] The following gives an application example of using the catalyst prepared in this example for piezophotocatalytic pure water decomposition:

[0044] Weigh 10 mg of the above-mentioned Na, Sm-CaBi2Nb2O9 / O V-BiOBr 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 30 minutes to remove oxygen under magnetic stirring; using a 300 W (λ≥ 420 nm) Xe lamp as the light source, piezoelectric photocatalytic pure water decomposition test was carried out under the ultrasonic action of 40 kHz and 110 W. 1 mL of gas was extracted every 30 minutes, and the H2 production was analyzed using gas chromatography; in addition, 1 mL of liquid product was taken every 30 minutes and mixed with KI / H 32 Mo7N6O 28 After the reaction, liquid ultraviolet analysis was carried out to obtain the production of H2O2; the calculated results are shown in Figure 6 and Figure 7 the curve c shown in

[0045] Example 4

[0046] A preparation method of an oxygen vacancy-free Na, Sm-CaBi2Nb2O9 / BiOBr piezoelectric photocatalyst, comprising the following steps:

[0047] Take 0.1575 g of Na, Sm-CaBi2Nb2O9 obtained in Example 2 and disperse it in 25 mL of pure water. After ultrasonic dispersion for 30 minutes, a suspension A was obtained; add 0.194 g of Bi(NO3)3·5H2O to the white suspension A and continuously stir for 30 minutes to obtain a white suspension B, then slowly drop 4 mL of saturated NaBr solution into the white suspension B and stir for 30 minutes to obtain a white suspension C; transfer the white suspension C into a stainless steel hydrothermal autoclave with a Teflon lining and react at 160 °C for 6 hours; the obtained precipitate was washed alternately with deionized water and absolute ethanol several times to obtain an oxygen vacancy-free Na, Sm-CaBi2Nb2O9 / BiOBr heterojunction piezoelectric photocatalyst with a shared (Bi2O2) 2+ interface; its X-ray diffraction pattern is as shown in Figure 1 the curve d shown in Figure 5 shown.

[0048] The following gives an application example of using the catalyst prepared in this example for piezoelectric photocatalytic pure water decomposition:

[0049] Weigh 10 mg of the above-mentioned 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 purge with Ar for 30 minutes under magnetic stirring; use a 300 W (λ ≥420 nm) Xe lamp as the light source, and conduct piezoelectric photocatalytic pure water decomposition tests under the ultrasonic action of 40 kHz and 110 W. Extract 1 mL of gas every 30 minutes and analyze the H2 production using gas chromatography; in addition, take 1 mL of the liquid product every 30 minutes and mix it with KI / H 32 Mo7N6O 28 Perform liquid ultraviolet analysis after the reaction to obtain the production of H2O2; the calculated results are shown in Figure 6 and Figure 7 curve d shown in

[0050] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications and substitutions should all be covered within the protection scope of the present invention.

Claims

1. A preparation method of Na, Sm-CaBi2Nb2O9 / O V -BiOBr piezoelectric photocatalyst, characterized in that The preparation method of the piezoelectric photocatalyst comprises the following steps: (1) Dispersing an appropriate amount of Na, Sm-CaBi2Nb2O9 and an appropriate amount of PVP in a certain amount of mannitol solution, and performing ultrasonic dispersion to obtain a white suspension; (2) Add an appropriate amount of Bi(NO3)3·5H2O and a saturated solution of an appropriate amount of NaBr to the above-mentioned suspension, stir at room temperature, treat the resulting white suspension at a certain temperature, and wash the obtained product alternately with deionized water and ethanol to finally obtain Na, Sm-CaBi2Nb2O9 / O 2+ with oxygen vacancies and having a shared (Bi2O2) V interface -BiOBr heterojunction piezoelectric photocatalyst.

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

3. The piezoelectric photocatalyst according to claim 1, wherein In step (1), adding 0.1 - 0.3 g of Na, Sm-CaBi2Nb2O9 prepared according to claim 2 and 0.3 - 0.5 g of PVP to 25 mL of mannitol solution, and performing ultrasonic dispersion for 30 minutes to obtain a white suspension A; wherein, the concentration of the mannitol solution is 0.05 - 0.2 M.

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

5. Use of the piezoelectric photocatalyst according to claims 1 to 4, characterized in that, Disperse the piezoelectric photocatalyst in pure water and then perform aeration for deoxygenation, and then decompose pure water to produce H2 and H2O2 under the combined action of visible light and ultrasound.

6. The application according to claim 5, wherein The dosage of the piezoelectric photocatalyst is 1 - 20 mg, and it is ultrasonically dispersed in 50 mL of pure water.

7. The application according to claim 5, wherein The gas used for deoxygenation is N2 or Ar, and the aeration time is 30 minutes.

8. The application according to claim 5, wherein The wavelength λ of the light source used for the catalytic reaction is ≥ 420 nm; the ultrasonic power used is 40 - 250 W.

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