A method for in-situ reduction synthesis of plasmonic heterojunction material and application thereof to piezoelectric-photocatalytic degradation of dye wastewater

Abstract

The application discloses a method for in-situ reduction synthesis of a plasma heterojunction material and application of the plasma heterojunction material in piezoelectric-photocatalytic degradation of dye wastewater. 12 The heterojunction catalyst can realize high-efficiency catalytic conversion through electronic mechanical coupling and solar-induced photogenerated carriers. When the material is applied to MB dye degradation, high piezoelectric-photocatalytic activity is exhibited. Compared with a piezoelectric or photocatalytic method alone, piezoelectric-photocatalysis is a high-efficiency environmental purification technology. In addition, the metal titanium template is first recycled for synthesis of the Bi / BTO catalyst, which is beneficial to commercial-scale application and industrial production.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation technology, and specifically relates to an in-situ reduction synthesis plasma method for Bi / Bi4Ti3O 12 Methods for using heterojunction materials and their application in the piezoelectric-photocatalytic degradation of dye wastewater. Background Technology

[0002] Photocatalysis is an effective method for mitigating excessive energy consumption and restoring ecological damage. However, the rapid recombination of photogenerated charge carriers reduces solar energy conversion efficiency. Piezoelectric-photocatalysis technology effectively modulates charge carrier dynamics by coupling the piezoelectric effect and the photoexcitation characteristics of semiconductors. Light irradiation generates charge carriers, while mechanical stress accelerates their separation. The piezoelectric polarization field induced by mechanical stress promotes carrier separation, thereby effectively modulating charge migration behavior at the semiconductor-piezoelectric interface and thus improving photocatalytic activity. Due to its superior reactivity compared to simple piezoelectric catalysis and photocatalysis, piezoelectric-photocatalysis has become an ideal catalytic technology, attracting widespread interest in environmental remediation and energy conversion.

[0003] Bismuth titanate (Bi4Ti3O) 12 BTO (bipolar-to-carbonyl oxidase) is a lead-free ferroelectric material. Due to its excellent photocatalytic activity, BTO has been widely used as a photocatalyst in wastewater treatment, H2 generation, and CO2 reduction. Therefore, the rational design of BTO holds promise for achieving a combination of piezoelectric and photocatalytic processes (i.e., piezoelectric-photocatalysis), enabling efficient energy capture and utilization. Summary of the Invention

[0004] Based on the technical problems existing in the prior art, the present invention provides an in-situ reduction synthesis plasma Bi / Bi4Ti3O 12 Methods for using (Bi / BTO) heterojunction materials and their application in piezoelectric-photocatalytic degradation of dye wastewater. The thin-layer morphology of BTO shortens the electron transfer distance and accelerates charge separation; the Bi nanoparticles on the surface act as electron traps, extending the carrier lifetime, thereby significantly improving the piezoelectric-photocatalytic performance of Bi / BTO.

[0005] The method for in-situ reduction synthesis of plasma heterojunction materials is as follows: using titanium foil as a template and titanium source, Na2Ti3O7 nanowires are first prepared by hydrothermal reaction of titanium foil with NaOH solution; bismuth nitrate is dissolved in NaOH solution and then hydrothermally reacted with Na2Ti3O7 nanowires to obtain Bi / Bi4Ti3O 12 Heterojunction materials.

[0006] The specific preparation steps of the Na2Ti3O7 nanowires are as follows: titanium foil is immersed in NaOH solution and subjected to a closed hydrothermal reaction at 120-200℃ for 10-25 hours; after the reaction is completed, it is naturally cooled to room temperature, washed alternately with deionized water and ethanol, and dried to obtain Na2Ti3O7 nanowires.

[0007] The Bi / Bi4Ti3O 12 The specific steps for preparing the heterojunction material are as follows: Bismuth nitrate is dissolved in NaOH solution, sonicated, and then reacted with Na2Ti3O7 nanowires in a sealed hydrothermal reaction at 120-200℃ for 36-50 hours; the mixture is washed alternately with deionized water and ethanol; finally, it is sonicated in water and dried to obtain Bi / Bi4Ti3O7 nanowires. 12 Heterojunction materials.

[0008] The concentration of the NaOH solution is 1-7 mol / L.

[0009] The concentration of bismuth nitrate dissolved in NaOH solution is 10-20 g / L.

[0010] The Bi / Bi4Ti3O prepared above 12 Application of heterojunction materials as piezoelectric-photocatalysts.

[0011] The piezoelectric-photocatalytic degradation method for dye wastewater is as follows: Bi / Bi4Ti3O 12 The heterojunction material was dispersed in dye wastewater and stirred in the dark for 20-40 minutes, followed by photocatalytic reaction under ultrasonic conditions.

[0012] In the photocatalytic reaction under ultrasonic conditions, the reaction temperature is controlled to not exceed 25°C.

[0013] The power of the ultrasound is 160-400W.

[0014] This invention employs a hydrothermal method to prepare, for the first time, an advanced semi-metallic Bi-modified Bi₄Ti₃O₂ by in-situ reduction without organic solvents. 12 (Bi / BTO) heterojunction catalyst. Bi in solution at high hydrothermal temperatures. 3+ It can be reduced in situ by Ti to metallic Bi NPs, and then deposited on BTO nanoplates to obtain Bi / Bi4Ti3O. 12In this heterojunction material, the in-situ reduction method not only preserves the two-dimensional structure of BTO but also forms a Schottky heterojunction at the interface. Bi NPs act as electron acceptors, inducing charge separation and improving the electron transfer rate at the interface. Combining the synergistic effect of the two-dimensional structure and the surface heterojunction, a highly efficient catalytic system is obtained, achieving efficient catalytic conversion through electromechanical coupling and solar-induced photogenerated carriers. Its application in the degradation of methylene blue (MB) exhibits high piezoelectric-photocatalytic activity. Within 70 minutes, the Bi / BTO catalyst achieves a piezoelectric-photocatalytic removal rate of 87.2% for methylene blue, with a rate constant of 0.0243 min. -1 The degradation performance was 2.23 times and 1.80 times that of pressure catalysis and photocatalysis, respectively. The improved degradation performance is attributed not only to the surface plasmon resonance effect of Bi nanoparticles, which enhances light absorption and accelerates charge separation, but also to Bi4Ti3O 12 The piezoelectric effect enhances the built-in electric field. Furthermore, this invention reveals the charge transfer mechanism through photoelectric response and reactive oxygen species capture experiments. Compared to piezoelectric or photocatalytic methods alone, piezoelectric-photocatalysis offers superior performance and is a highly efficient environmental remediation technology. The titanium template used in this invention is the first to be recyclable for synthesizing Bi / BTO catalysts, facilitating commercial-scale applications and industrial production. This invention provides an effective strategy for designing highly efficient heterojunction catalytic technologies that utilize solar and mechanical energy from nature for environmental remediation. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the synthesis process of the Bi / BTO heterojunction of the present invention.

[0016] Figure 2 This is a comparison diagram of XRD spectra from an embodiment of the present invention.

[0017] Figure 3 The images are (a) SEM images of NTO-5M and (bc) Bi / BTO-5M of the present invention; (d) TEM image, (e) HRTEM image and (f) SAED image of Bi / BTO-5M; (g) HAADF-STEM image and corresponding elemental spectrum image of Bi / BTO-5M.

[0018] Figure 4 (a) and (b) are SEM and TEM images of the BTO of the present invention, (c) SAED image, (d) HAADF-STEM image and corresponding elemental spectrum image.

[0019] Figure 5 The present invention relates to Bi / BTO-5M and Bi4Ti3O 12XPS spectra of the samples: (a) full-range spectrum and (b) high-resolution spectra of Bi4f, (c) O1s and (d) Ti2p.

[0020] Figure 6 The following are PFM images of the Bi / BTO-5M nanoplates of the present invention: (a) morphology, (b) piezoelectric response amplitude, (c) piezoelectric response phase difference relative to an applied electric field, (d) local phase-voltage hysteresis loop, and (e) amplitude-voltage loop measured from a selected region; finite element simulations were performed on the piezoelectric potential distributions of (f) Bi / BTO-5M and (g) BTO.

[0021] Figure 7 (a) and (b) are piezoelectric catalytic activity and degradation efficiency graphs of methylene blue for different samples of the present invention, (c) piezoelectric degradation kinetic curves and (d) the corresponding reaction constant k; (e) piezoelectric, photocatalytic and piezoelectric-photocatalytic degradation activity graphs of methylene blue and (f) the corresponding degradation kinetic curves.

[0022] Figure 8 The present invention presents the time-dependent UV-Vis absorption spectra of MB using different catalytic schemes: (a) piezoelectric catalysis; (b) photocatalysis; (c) piezoelectric-photocatalysis.

[0023] Figure 9 The piezoelectric-photocatalytic degradation performance of Bi / BTO-5M under different conditions of the present invention is as follows: (a) ultrasonic power, (b) pH value, (c) MB concentration, (d) catalyst dosage.

[0024] Figure 10 These are the piezoelectric-photocatalytic degradation efficiency and degradation kinetic curves of methylene blue under different ultrasonic powers (a) and (b) and different pH values ​​(c) and (d) of this invention.

[0025] Figure 11 These are the piezoelectric-photocatalytic degradation efficiency and degradation kinetic curves of (a) and (b) different concentrations of MB and (c) and (d) different amounts of catalyst in this invention.

[0026] Figure 12 The present invention includes (a) the DRS spectrum of the prepared sample and (b) the band gap; (c) the N2 absorption-desorption curve and pore size (inset); (d) the photoluminescence spectrum of the prepared sample; (e) the transient photocurrent response; and (f) the EIS.

[0027] Figure 13 The present invention is (a) DMPO- · O2 - and (b)DMPO- ·(c) ESR spectrum of DMPO spin trapping on Bi / BTO-5M after OH irradiation for 5 minutes. (d) Piezoelectric-photocatalytic degradation activity of MB on Bi / BTO-5M in the presence of different scavengers.

[0028] Figure 14 The piezoelectric-photocatalytic performance of the Bi / BTO-5M catalyst of the present invention in the degradation of methylene blue is shown in the following: (a) cycle test; (b) piezoelectric photodegradation of MB in different water samples; (cd) cycle test of Ti template: piezoelectric-photocatalytic activity and degradation efficiency of methylene blue. Detailed Implementation

[0029] The specific embodiments of the present invention will be further described in detail below with reference to examples and comparative examples.

[0030] Example 1:

[0031] 1) Preparation of Na2Ti3O7-1M nanowires (NTO-1M):

[0032] Titanium foil (2×5×0.1cm) was ultrasonically cleaned with deionized water and anhydrous ethanol. 3 The titanium foil was then dried. Next, the titanium foil was immersed in a 1 mol / L NaOH solution and placed in a 50 mL Teflon autoclave. The reaction was carried out at 200 °C for 15 hours. After the reaction was complete, the product was allowed to cool naturally to room temperature. It was then washed alternately with deionized water and ethanol to remove surface-adsorbed impurities, and finally dried at 60 °C for 10 hours to obtain Na₂Ti₃O₇-1M nanowires, abbreviated as NTO-1M.

[0033] 2)Bi / Bi4Ti3O 12 Preparation of -1M (Bi / BTO-1M):

[0034] The Bi / BTO catalyst was obtained through in-situ reduction without the use of organic solvents. Bismuth nitrate (0.5 g) was dissolved in 35 mL of NaOH (3 mol / L) solution and sonicated to form a homogeneous reaction solution. This solution was then placed in a sealed Teflon autoclave containing the NTO obtained in step 1) and subjected to hydrothermal treatment at 200 °C for 48 hours. After treatment, the catalyst was washed alternately with deionized water and ethanol. Finally, it was sonicated in water for 30 minutes and dried at 60 °C to obtain Bi / Bi4Ti3O. 12 -1M heterojunction material, abbreviated as Bi / BTO-1M.

[0035] 3) Wastewater treatment capacity of Bi / BTO-1M:

[0036] The catalytic performance of the prepared samples was tested by degrading MB dye. A xenon lamp (300W) was used as the light source, and an ultrasonic cleaner (400W, 40kHz) provided ultrasonic vibration. 10 mg of Bi / BTO-1M catalyst was dispersed in 150 mL of MB aqueous solution (5 mg / L) and magnetically stirred in the dark for 30 minutes to reach adsorption-desorption equilibrium. The catalytic reaction was then irradiated with xenon lamp under ultrasonic conditions. During the reaction, the water temperature in the ultrasonic cleaner was maintained below 25°C using circulating cooling water to eliminate the effects of heat. 1.5 mL of the suspension was removed every 5 minutes and centrifuged for 3 minutes to remove the catalyst. Subsequently, the absorption spectrum of the MB aqueous solution at the maximum absorption peak at approximately 664 nm was measured using UV-Vis spectrophotometry. Figure 7 As shown in b, the piezoelectric catalytic degradation rate of Bi / BTO-1M was 60.6% within 120 minutes.

[0037] Example 2:

[0038] 1) Preparation of Na2Ti3O7-3M nanowires (NTO-3M):

[0039] Na₂Ti₃O₇ nanowires were prepared via a hydrothermal synthesis method using titanium foil as a template and titanium source. First, the titanium foil (2×5×0.1cm) was ultrasonically cleaned with deionized water and anhydrous ethanol. 3 The titanium foil was then dried. Next, the titanium foil was immersed in a 3 mol / L NaOH solution and placed in a 50 mL Teflon autoclave. The reaction was carried out at 200 °C for 15 hours. The product was thoroughly washed with deionized water and ethanol to remove surface-adsorbed impurities. After the reaction was complete, the product was allowed to cool naturally to room temperature and then dried at 60 °C for 10 hours to obtain Na₂Ti₃O₇₇₃M, abbreviated as NTO₃M.

[0040] 2)Bi / Bi4Ti3O 12 Preparation of -3M (Bi / BTO-3M):

[0041] Same as step 2) of Example 1, to obtain Bi / Bi4Ti3O 12 -3M heterojunction material, abbreviated as Bi / BTO-3M.

[0042] 3) Wastewater treatment capacity of Bi / BTO-3M:

[0043] The catalytic performance of the prepared samples was tested by degrading MB dye. A xenon lamp (300W) was used as the light source, and an ultrasonic cleaner (400W, 40kHz) provided ultrasonic vibration. 10 mg of Bi / BTO-1M catalyst was dispersed in 150 mL of MB aqueous solution (5 mg / L) and magnetically stirred in the dark for 30 minutes to reach adsorption-desorption equilibrium. The catalytic reaction was then catalyzed under ultrasonic conditions by xenon lamp irradiation. During the reaction, the water temperature in the ultrasonic cleaner was maintained below 25°C using circulating cooling water to eliminate the effects of heat. 1.5 mL of suspension was removed every 5 minutes and centrifuged for 3 minutes to remove the catalyst. Subsequently, the absorption spectrum of the MB aqueous solution at the maximum absorption peak at approximately 664 nm was measured using UV-Vis spectrophotometry. Figure 7 As shown in b, the piezoelectric catalytic degradation rate of Bi / BTO-3M was 65.9% within 120 minutes.

[0044] Example 3:

[0045] 1) Preparation of Na2Ti3O7-5M nanowires (NTO-5M):

[0046] Na₂Ti₃O₇ nanowires were prepared via a hydrothermal synthesis method using titanium foil as a template and titanium source. First, the titanium foil (2×5×0.1cm) was ultrasonically cleaned with deionized water and anhydrous ethanol. 3 The titanium foil was then dried. Next, the titanium foil was immersed in a 5 mol / L NaOH solution and placed in a 50 mL Teflon autoclave. The reaction was carried out at 200 °C for 15 hours. After the reaction was complete, the product was allowed to cool naturally to room temperature. It was then thoroughly washed with deionized water and ethanol to remove surface-adsorbed impurities, and finally dried at 60 °C for 10 hours to obtain Na₂Ti₃O₇₇₅M, abbreviated as NTO₅M.

[0047] 2)Bi / Bi4Ti3O 12 Preparation of -5M (Bi / BTO-5M):

[0048] Same as step 2) of Example 1, to obtain Bi / Bi4Ti3O 12 -5M heterojunction material, abbreviated as Bi / BTO-5M.

[0049] 3) Wastewater treatment capacity of Bi / BTO-5M:

[0050] The catalytic performance of the prepared samples was tested by degrading MB dye. A xenon lamp (300W) was used as the light source, and an ultrasonic cleaner (400W, 40kHz) provided ultrasonic vibration. 10 mg of Bi / BTO-1M catalyst was dispersed in 150 mL of MB aqueous solution (5 mg / L) and magnetically stirred in the dark for 30 minutes to reach adsorption-desorption equilibrium. The reaction was then catalyzed under ultrasonic conditions by xenon lamp irradiation. During the reaction, the water temperature in the ultrasonic cleaner was maintained below 25°C using circulating cooling water to eliminate the effects of heat. 1.5 mL of the suspension was removed every 5 minutes and centrifuged for 3 minutes to remove the catalyst. Subsequently, the absorption spectrum of the MB aqueous solution at the maximum absorption peak at approximately 664 nm was measured by UV-Vis spectrophotometry. Among all Bi / BTO heterostructures, Bi / BTO-5M exhibited the best piezoelectric catalytic activity, achieving a degradation rate of 73.4% within 120 minutes. Figure 7 ad).

[0051] The composite material prepared above was characterized and tested:

[0052] The morphology of NTO, BTO, and Bi / BTO-5M samples was observed using scanning electron microscopy and electron microscopy. Figure 3 and Figure 4 The NTO-5M sample exhibits a nanowire morphology. The pure BTO sample exhibits a rectangular nanoplate shape with vertically intersecting nanoplates. Figure 4 ab), with an average thickness of 225nm. Figure 4 a). The Bi / BTO-5M composite material exhibits regularly rectangular nanosheets with reduced thickness ( Figure 3 These nanosheets are randomly stacked, with an average thickness of 80 nm. Using titanium foil as a growth template ensures the uniform dispersion of the Bi / BTO-5M nanosheets, effectively preventing BTO aggregation. Furthermore, the layered structure of Bi / BTO-5M not only exposes more adsorption and active sites but also generates greater deformation and stronger piezoelectric potential under stress, thereby enhancing the built-in electric field and improving piezoelectric catalytic performance. Specifically, the Bi / BTO-5M composite material exhibits clearly defined rectangular nanoplates (…). Figure 3 d), consistent with the scanning electron microscopy results. The lattice fringes indicate that the interplanar spacings of 0.328, 0.297, and 0.411 nm correspond to the (012) plane of Bi, the (117) plane of BTO, and the (008) plane, respectively. Figure 3 e). In the selected area electron diffraction (SAED) pattern ( Figure 3f and 4c), the Bi and BTO phases are marked with yellow and blue circles, respectively, corresponding to the respective lattice planes (202) and (317), verifying the successful formation of the Bi / BTO heterojunction. Furthermore, HAADF-STEM and EDS elemental spectra show that Bi, O, and Ti elements are uniformly distributed in the BTO and Bi / BTO-5M samples. Figure 4 d and Figure 3 g).

[0053] XPS analysis was used to analyze the chemical state and elemental composition of the composite material. Full-range XPS spectroscopy indicated that the Bi / BTO-5M sample was mainly composed of Bi, Ti, and O elements. Figure 5 a). The O1s spectrum shows two symmetrical Gaussian curves at approximately 529.8 eV and 531.9 eV (a). Figure 5 b) is attributed to lattice oxygen BTO and surface hydroxyl groups, respectively. The Ti 2p spectrum shows an asymmetric double peak with binding energies of 458.1 and 464.5 eV, corresponding to Ti 4+ Ti 2p 3 / 2 and Ti 2p 1 / 2 state( Figure 5 b). The two peaks at 164.4 and 159.0 eV can be attributed to Bi. 3+ Bi 4f 5 / 2 and Bi 4f 7 / 2 The two small peaks at 157.5 eV and 163.6 eV belong to Bi metal, which confirms that Ti successfully converted Bi metal under hydrothermal conditions. 3+ The ions were reduced to elemental Bi. Notably, after Bi modification, the binding energy between Bi 4f and O 1s was higher than that of the original BTO, indicating a strong electronic interaction between Bi and BTO. This electronic coupling promotes the efficient separation and transfer of photogenerated charges, thereby enhancing catalytic activity.

[0054] When a piezoelectric material is deformed under external force, its polarization state changes, thereby generating a piezoelectric electromotive force. This invention uses piezoelectric microscopy (PFM) to study the morphology and local piezoelectric response of Bi / BTO-5M nanoplates. A direct current (DC) bias was applied to the tip of the probe covering the Pt coating, inducing sample deformation through the inverse piezoelectric effect to evaluate the piezoelectric response. An alternating current (AC) voltage of 1V was applied to obtain the phase and amplitude of the piezoelectric signal. The morphology of the Bi / BTO-5M sample is shown below. Figure 6 As shown in Figure a, the amplitude and out-of-plane phase of the piezoelectric response are respectively as follows: Figure 6 As shown in bc, the amplitude image of the piezoelectric response reveals the surface contrast, indicating the presence of the piezoelectric effect. Furthermore, Figure 6c shows the phase difference between the applied electric field and the polarization field in the Bi / BTO-5M sample. The local surface piezoelectric responses between individual grains are different and may vary with location. Therefore, the existence of local piezoelectricity in Bi / BTO-5M can only be qualitatively confirmed. The polarization direction and piezoelectric response intensity of the ferroelectric material are displayed by different contrasts of phase and amplitude PFM images, respectively. When the tip bias voltage is adjusted from -10V to 10V, a phase switching of ~180° and a butterfly-shaped amplitude curve are observed in four different regions of the Bi / BTO-5M nanoplate. Figure 6 This corresponds to the strain-electric field (SE) curve of piezoelectric materials. PFM results show that Bi / BTO-5M has strong ferroelectric polarization.

[0055] It is well known that reducing the thickness of nanosheets often leads to greater deformation, thereby generating an ideal piezoelectric potential. Therefore, to investigate the effect of BTO nanosheet thickness on piezoelectric potential, this invention uses the finite element method (FEM) to simulate the piezoelectric potential generated under ultrasonic stimulation. Figure 6 (fg). Ultrasonic vibration induces the formation and collapse of cavitation bubbles in water, generating localized shock waves with peak pressures of approximately 100 MPa. These shock waves impact the surfaces of adjacent nanocrystals, causing mechanical deformation and piezoelectric effects. The simulated dimensions of Bi / BTO-5M and BTO were set to 825 × 500 × 40 nm, respectively. 3 and 785×400×225nm 3 These were obtained through SEM and TEM results. The material parameters of bismuth titanate include density (ρ), Poisson's ratio (Y), Young's modulus (E), and coupling coefficient (k). 15 ,k 31 ,k 33 and relative permittivity These parameters were obtained or calculated from previous literature. When subjected to an ultrasonic pressure of 100 MPa, the maximum piezoelectric potential difference of the Bi / BTO-5M nanosheets (0.176 V) is approximately 20 times that of pure BTO (0.0828 V). Figure 6 The enhanced piezoelectric potential of Bi / BTO-5M nanosheets is likely due to their more deformable two-dimensional morphology and larger planar size, which gives them a stronger ability to trap mechanical energy. This enhanced piezoelectric potential generally facilitates the efficient separation and transport of piezoelectric free charges. With heterogeneous bonding between surface-loaded Bi particles, Bi / BTO-5M exhibits stronger charge separation and migration capabilities, thereby enabling more charges to participate in the degradation of methylene blue.

[0056] To characterize the piezoelectric catalytic performance of Bi / BTO, BTO, and the commercial piezoelectric catalyst PVDF, the degradation of MB dye at a concentration of 5 mg / L was investigated under ultrasonic vibration. Figure 7 Without a catalyst, only a small amount of methylene blue (9.3%) can be degraded. Figure 7 a), while the Bi / BTO catalyst improved the degradation activity ( Figure 7 (b) Among all Bi / BTO heterostructures, Bi / BTO-5M exhibited the best piezoelectric catalytic activity, achieving a degradation rate of 73.4% within 120 minutes. The piezoelectric degradation rate of Bi / BTO-5M (73.4%) was approximately 2.7 times that of BTO (27.3%) and 4.1 times that of PVDF (18.1%). However, the catalytic performance of Bi / BTO-7M decreased slightly. This difference may be due to the aggregation of BiNPs in the supersaturated Bi / BTO-7M, leading to carrier recombination. Therefore, the amount of BiNPs should be reasonably controlled to achieve a balance between proton excitation and hole-electron recombination, thereby obtaining the optimal piezoelectric catalytic activity. The methylene blue degradation kinetic curves of different samples are shown in [Figure number missing]. Figure 7 c. The relationship between ln(C0 / C) and piezoelectric catalysis time t shows a good linear correlation, which is very consistent with the characteristics of the apparent first-order kinetic reaction (lnC0 / C=k×t). Figure 7 As shown in d, the reaction rate constant of Bi / BTO-5M is 0.00773 min. -1 The values ​​are BTO (0.00178 min). -1 ) and PVDF (0.00129min -1 The activity enhancement was approximately 4.3 times and 6.0 times that of Bi / BTO-5M. This significant activity enhancement can be attributed to Bi and Bi4Ti3O in Bi / BTO-5M. 12 The unique combination of these elements produces a synergistic effect. Bi semimetals can act as proton-assisted catalysts, promoting piezoelectric electron transfer through Schottky junctions, thereby enhancing catalytic activity. This is similar to the role of noble metals, indicating the great potential of using economical Bi to replace noble metals to improve catalytic efficiency.

[0057] To reveal the plasma-catalyzed BiNPs and Bi4Ti3O 12 This invention comprehensively investigates the synergistic effect of the induced piezoelectric effect on the catalytic performance of Bi / BTO-5M heterojunction materials, including illumination, ultrasound, and the coupling of light and ultrasound. With prolonged catalytic time, the concentration of the methylene blue solution rapidly decreases (…). Figure 8 It is worth noting that using light irradiation or ultrasonic vibration alone only yielded low photocatalytic degradation efficiencies, at 70.3% and 62.1%, respectively. Figure 7 e). Furthermore, under the coupled effect of ultrasonic vibration and light irradiation, the removal rate of methylene blue can be further increased to 87.2%. The piezoelectric-photocatalytic rate constant k of the Bi / BTO-5M heterojunction material is 0.02430 min.-1 These figures are 2.23 times and 1.80 times that of pressure catalysis and photocatalysis, respectively. Figure 7 f). Furthermore, the photocatalytic activity of Bi / BTO-5M surpassed that of piezoelectric catalysis, indicating its superior ability to promote efficient charge transfer. These results highlight the crucial role of the synergistic effect between appropriate control of carrier concentration and superior ferroelectric properties in determining piezoelectric catalytic performance. The synergistic effect of photocatalysis and piezoelectric catalysis further accelerates charge transfer within the catalyst, thereby promoting electron transfer between the charge and electroactive substances in the surrounding environment, ultimately enhancing overall catalytic activity.

[0058] To gain a deeper understanding of the piezoelectric-photocatalytic performance of Bi / BTO-5M, this invention conducted extensive research, exploring the effects of ultrasonic power, pH value, methylene blue concentration, and catalyst dosage. Figure 9-11 ).like Figure 9 As shown in Figure a, the piezoelectric-photocatalytic properties are significantly affected by the ultrasonic frequency. The optimal piezoelectric-photocatalytic performance of Bi / BTO-5M material is achieved at 400 W and 40 kHz. Higher ultrasonic power leads to more pronounced catalyst deformation and a stronger piezoelectric field. This enhanced piezoelectric field promotes the effective separation of photogenerated electrons and holes, ultimately improving the piezoelectric-photocatalytic activity. Furthermore, increasing the pH from 10.5 to 13.0 also significantly improved the piezoelectric-photocatalytic performance of Bi / BTO-5M, achieving a degradation efficiency of 98.3%, with methylene blue almost completely degraded within 9 minutes. Figure 9 b and 10c-d). It is worth noting that the rate constant k of Bi / BTO-5M is 0.36925 min. -1 Compared to the reported synthesis of Bi4Ti3O by calcination 12 Its rate constant is about 105 times higher than that of Bi4Ti3O. 12 Compared to nanofibers, Bi / BTO-5M nanoplatelets exhibit significantly superior catalytic performance, exceeding the k-value of most reported piezoelectric materials. Conversely, decreasing the pH to 3.0 leads to a slower degradation rate. The difference in catalytic performance at different pH values ​​is mainly attributed to the varying absorption capacity of the target molecules by the Bi / BTO-5M nanoplatelets. This finding highlights the crucial role of effective interactions between organic molecules and the catalyst in enhancing catalytic activity. Therefore, Bi / BTO-5M nanoplatelets are suitable for piezoelectric-photocatalysis in alkaline environments. Clearly, the degradation efficiency gradually decreases with increasing initial methylene blue concentration. Figure 9 c and Figure 11(ab). This means that the number of active sites available for catalytic reactions is limited. Therefore, increasing the dye concentration may exceed the capacity of the active sites, leading to a decrease in catalytic efficiency. Furthermore, excess charged dye molecules in solution may occupy active sites through electrostatic attraction. This effect subsequently shields the polarization charge of the Bi / BTO-5M nanoplate, resulting in a decline in catalytic performance. Figure 9 d and Figure 11 As shown in Figure cd, the piezoelectric-photocatalytic degradation efficiency of Bi / BTO-5M increases with increasing catalyst mass, reaching a maximum of 30 mg. This improvement is attributed to the increased number of active sites resulting from the increased catalyst dosage, thereby generating more active free radicals during the catalytic process.

[0059] Example 4:

[0060] 1) Preparation of Na2Ti3O7-7M nanowires (NTO-7M):

[0061] Na₂Ti₃O₇ nanowires were prepared via a hydrothermal synthesis method using titanium foil as a template and titanium source. First, the titanium foil (2×5×0.1cm) was ultrasonically cleaned with deionized water and anhydrous ethanol. 3 The titanium foil was then dried. Next, the titanium foil was immersed in a 5 mol / L NaOH solution and placed in a 50 mL Teflon autoclave. The reaction was carried out at 200 °C for 15 hours. After the reaction was complete, the product was allowed to cool naturally to room temperature. It was then thoroughly washed with deionized water and ethanol to remove surface-adsorbed impurities, and finally dried at 60 °C for 10 hours to obtain Na₂Ti₃O₇₇M, abbreviated as NTO₇M.

[0062] 2)Bi / Bi4Ti3O 12 Preparation of -7M (Bi / BTO-7M):

[0063] Same as step 2) of Example 1, to obtain Bi / Bi4Ti3O 12 -7M heterojunction material, abbreviated as Bi / BTO-7M.

[0064] 3) Wastewater treatment capacity of Bi / BTO-7M:

[0065] The catalytic performance of the prepared samples was tested by degrading MB dye. A xenon lamp (300W) was used as the light source, and an ultrasonic cleaner (400W, 40kHz) provided ultrasonic vibration. 10 mg of Bi / BTO-1M catalyst was dispersed in 150 mL of MB aqueous solution (5 mg / L) and magnetically stirred in the dark for 30 minutes to reach adsorption-desorption equilibrium. The catalytic reaction was then catalyzed under ultrasonic conditions by xenon lamp irradiation. During the reaction, the water temperature in the ultrasonic cleaner was maintained below 25°C using circulating cooling water to eliminate the effects of heat. 1.5 mL of suspension was removed every 5 minutes and centrifuged for 3 minutes to remove the catalyst. Subsequently, the absorption spectrum of the MB aqueous solution at the maximum absorption peak at approximately 664 nm was measured using UV-Vis spectrophotometry. Figure 7 As shown in b, the pressure catalytic degradation rate of Bi / BTO-7M was 69.5% within 120 minutes.

[0066] Compare with Example 1:

[0067] 1) Preparation of Na₂Ti₃O₇ nanowires (NTO):

[0068] 1.60 g of TiO2 powder was dispersed in 35 mL of NaOH (10 mol / L) aqueous solution and sonicated to form a homogeneous reaction solution. This solution was then transferred to a 50 mL Teflon autoclave. After sealing, the autoclave was placed in a 240 °C oven for 24 h of hydrothermal treatment. The resulting Na2Ti3O7 nanowires were washed several times with deionized water and anhydrous ethanol until the pH of the filtrate was close to neutral. The product was then dried in a 60 °C oven to obtain Na2Ti3O7, abbreviated as NTO.

[0069] 2)Bi4Ti3O 12 Preparation of (BTO):

[0070] Weigh 0.97 g Bi(NO3)3·5H2O and 0.15 g Na2Ti3O7 and dissolve them in 35 mL NaOH (3 mol / L). Sonicate the solution for 30 min to form a homogeneous solution. Transfer the solution to a 50 mL Teflon autoclave. Seal the autoclave and place it in a 200℃ oven for 48 h of hydrothermal treatment. After the reaction, allow it to cool naturally to room temperature. Wash the precipitate alternately with deionized water and ethanol until neutral, then centrifuge to remove impurities adsorbed on the surface of the composite material. Dry the precipitate in a 60℃ oven to obtain Bi4Ti3O7. 12 It is abbreviated as BTO.

[0071] 3) BTO's wastewater treatment capacity:

[0072] The catalytic performance of the prepared samples was tested by degrading MB dye. A xenon lamp (300W) was used as the light source, and an ultrasonic cleaner (400W, 40kHz) provided ultrasonic vibration. 10 mg of Bi / BTO-1M catalyst was dispersed in 150 mL of MB aqueous solution (5 mg / L) and magnetically stirred in the dark for 30 minutes to reach adsorption-desorption equilibrium. The catalytic reaction was then catalyzed under ultrasonic conditions by xenon lamp irradiation. During the reaction, the water temperature in the ultrasonic cleaner was maintained below 25°C using circulating cooling water to eliminate the effects of heat. 1.5 mL of suspension was removed every 5 minutes and centrifuged for 3 minutes to remove the catalyst. Subsequently, the absorption spectrum of the MB aqueous solution at the maximum absorption peak at approximately 664 nm was measured using UV-Vis spectrophotometry. Figure 7 As shown in b, the pressure catalytic degradation rate of BTO is only 27.3% within 120 minutes.

[0073] Compare with Example 2:

[0074] 1) Preparation of Na2Ti3O7-5M nanowires (NTO-5M):

[0075] Following step 1) of Example 3, after obtaining Na2Ti3O7-5M, the titanium foil was ultrasonically treated in water for 30 minutes and the material was collected. Then it was dried at 60°C to obtain powdered Na2Ti3O7-5M material, abbreviated as NTO-5M-2.

[0076] 2) Preparation of NBTO:

[0077] Bismuth nitrate (0.5 g) was dissolved in 35 mL of NaOH (3 mol / L) solution and sonicated to form a homogeneous reaction solution. This solution was then placed in a sealed Teflon autoclave containing NTO-5M-2 obtained in step 1) and subjected to hydrothermal treatment at 200 °C for 48 hours. After the reaction was complete, the mixture was allowed to cool naturally to room temperature, washed with deionized water and ethanol by centrifugation, and then centrifuged again to remove impurities adsorbed on the surface of the composite material. Finally, the mixture was dried in an oven at 60 °C to obtain the NBTO material.

[0078] X-ray powder diffraction (XRD) characterized the crystal structure of the material. Under alkaline conditions, NTO powder scraped from titanium foil was reacted with Bi(NO)3; no metallic Bi(NO)3 was formed from the NTO. Figure 2(b) This indicates that metallic Ti acts as a reducing agent. Under external force, the polarization centers of the piezoelectric material split and generate a piezoelectric potential. Therefore, the catalytic reaction of piezoelectric semiconductors, which possess both photocatalytic and piezoelectric properties, is modulated by external stress (such as ultrasound, stirring, etc.). On the one hand, the piezoelectric field can be used to promote the separation of photogenerated charge carriers, i.e., the piezoelectric-photocatalytic effect. On the other hand, free charges in the semiconductor can be separated by the piezoelectric field under light-free conditions and participate in the catalytic degradation of pollutants, i.e., piezoelectric catalysis. Piezoelectric catalysis can achieve the decomposition of pollutants under light-free conditions, which has unique advantages.

[0079] The enhanced piezoelectric-photocatalytic performance of the Bi / BTO-5M sample can be attributed to the synergistic effect of the two-dimensional nanoplates of BTO and the surface Schottky heterostructure of Bi / BTO. This leads to the conclusion that constructing heterostructures through in-situ reduction of Bi NPs is an effective method to improve piezoelectric-photocatalytic activity. The metallic bismuth generated on BTO forms a Schottky barrier at their contact interface. Electrons excited by light and ultrasound can rapidly transfer from the conduction band of BTO to Bi NPs, thereby promoting directional electron migration, participating in the formation of surface ROS, and enhancing catalytic activity.

[0080] Figure 13 The mechanism of Bi / BTO piezoelectric-photocatalytic degradation of biomass (MB) is described in section d. Based on the SPR effect and unique photogenerated charge transfer pathway of Bi NPs, the Bi / BTO heterojunction possesses a suitable redox potential for enhanced light absorption, promoted charge separation, and the generation of reactive oxygen species (ROS). The Fermi level of Bi is approximately -0.17 eV (relative to NHE), which is more positive than the bottom conduction band (CB) of BTO. Therefore, under light irradiation, electrons generated on the conduction band of BTO can rapidly migrate to Bi NPs, which act as electron traps to capture and transfer photogenerated electrons, thus more effectively separating photogenerated charges. Subsequently, the electrons accumulated on the Bi NPs are consumed by the surrounding oxygen, forming ROS. The following reaction equation summarizes the process of piezoelectric-photocatalytic MB degradation:

[0081] Bi / BTO+light+ultrasound→Bi / BTO(e - +h + (1)

[0082] e - +O2→ · O2 - (2)

[0083] H2O+h + →H + + · OH (3)

[0084] · OH+· OH→H2O2 (4)

[0085] · O2 - +e - +2H + →H2O2 (5)

[0086] · OH + H₂O₂ → H + +H2O+ · O2 - (6)

[0087] e - +H₂O₂ + H⁺ → · OH + H₂O (7)

[0088] To meet the requirements of industrial applications, catalyst stability is a critical factor to consider. Therefore, a cyclic experiment was conducted on the photo-piezoelectric degradation of methylene blue using Bi / BTO-5M. Notably, the Bi / BTO-5M catalyst retained 95% of its activity after five cycles. Figure 14 a) It exhibits excellent stability and reproducibility. Furthermore, the environmental adaptability of the Bi / BTO-5M catalyst in different water sources, including deionized water, tap water, and river water, was investigated. Figure 14 (bc). The results showed that the removal rates of tap water and river water were 66.9% and 55.6%, respectively. The lower removal rate of tap water was due to the presence of chlorination disinfection byproducts, which, along with h... + and · The binding of OH groups inhibits the oxidation of MB by free radicals. This finding suggests that Bi / BTO-5M holds promise as a highly efficient catalyst for practical wastewater treatment under various environmental conditions.

[0089] Titanium foil can not only serve as a stable titanium source, but it can also be recycled to synthesize Bi / BTO catalysts. Figure 13 Figure d shows the piezoelectric-photocatalytic removal rate of methylene blue (MB) by Bi / BTO-5M within five template usage cycles. The piezoelectric-photocatalytic degradation efficiency of methylene blue gradually decreased with increasing template usage. Figure 13 d). However, even after five uses of the template, the degradation efficiency remained high, meeting the requirements for practical applications. These findings further confirm the potential applications of Bi / BTO catalysts in various industrial environments and environmental remediation.

[0090] The present invention has been disclosed above with reference to preferred embodiments, but it is not intended to limit the present invention. All technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for in-situ reduction synthesis of plasma heterojunction materials, characterized in that, The specific operation of the method is as follows: using titanium foil as a template and titanium source, Na2Ti3O7 nanowires are first prepared by reacting the titanium foil with NaOH solution using a hydrothermal method; bismuth nitrate is dissolved in NaOH solution and then reacted with Na2Ti3O7 nanowires hydrothermally to obtain Bi / Bi4Ti3O 12 Heterojunction materials.

2. The method according to claim 1, characterized in that, The specific preparation steps of the Na2Ti3O7 nanowires are as follows: titanium foil is immersed in NaOH solution and subjected to a closed hydrothermal reaction at 120-200℃ for 10-25 hours; after the reaction is completed, it is naturally cooled to room temperature, washed alternately with deionized water and ethanol, and dried to obtain Na2Ti3O7 nanowires.

3. The method according to claim 1, characterized in that, The Bi / Bi4Ti3O 12 The specific steps for preparing the heterojunction material are as follows: Bismuth nitrate is dissolved in NaOH solution, sonicated, and then reacted with Na2Ti3O7 nanowires in a sealed hydrothermal reaction at 120-200℃ for 36-50 hours; the mixture is washed alternately with deionized water and ethanol; finally, it is sonicated in water and dried to obtain Bi / Bi4Ti3O7 nanowires. 12 Heterojunction materials.

4. The method according to claim 1, characterized in that, The concentration of the NaOH solution is 1-7 mol / L.

5. The method according to claim 1, characterized in that, The concentration of bismuth nitrate dissolved in NaOH solution is 10-20 g / L.

6. The Bi / Bi4Ti3O prepared by the method according to any one of claims 1-5 12 Application of heterojunction materials as piezoelectric-photocatalysts.

7. A method for piezoelectric-photocatalytic degradation of dye wastewater, characterized in that, The specific operation of the method is as follows: The Bi / Bi4Ti3O prepared by the method according to any one of claims 1-5 is... 12 The heterojunction material was dispersed in dye wastewater and magnetically stirred in the dark for 20-40 minutes, followed by photocatalytic reaction under ultrasonic conditions.

8. The method according to claim 7, characterized in that, In the photocatalytic reaction under ultrasonic conditions, the reaction temperature is controlled to not exceed 25°C.

9. The method according to claim 7, characterized in that, The power of the ultrasound is 160-400W.

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